久世 信彦

<title>ABSTRACT</title> Molecules in diffuse and translucent clouds experience cooling as a result of radiation and less excitation from collisions. However, rotation around a molecular axis of acetonitrile, CH3CN, cannot be cooled by radiation, causing rotational populations to concentrate at the J = K levels. We aim to search for absorption lines of CH3CN having J = K level concentrations in diffuse and translucent clouds. The JK = 43–33 transition at 73.6 GHz was investigated toward Sgr B2(M) in the Galactic Centre region and other sources, using the Nobeyama 45-m telescope. Based on the absorption lines detected toward Sgr B2(M), a radiation temperature of 2.8 ± 0.5 K, kinetic temperature of 88 ± 29 K and column density of (1.35 ± 0.14) × 1014 cm−2 were derived for this molecule, revealing extremely concentrated J = K levels due to the lower excitation temperature and higher kinetic temperature. The absorption lines occurred at a velocity of 64 km s−1. The results confirm that CH3CN with J = K level concentrations exists in the envelope of Sgr B2(M).

The central (Nc) and terminal (Nt) nitrogen K-shell photoelectron spectra (PESs) of N2O molecules have been measured in the σ shape resonance energy region at temperatures of ∼300 and ∼630 K. Estimating vibrational populations based on the Boltzmann distribution at these temperatures, PESs of vibrationally ground and bending-excited levels in the initial electronic ground state were extracted. Vibrationally integrated partial cross sections and asymmetry parameters for ionization from vibrationally ground and bending-excited levels were obtained as a function of the incident photon energy by integrating PESs over the vibrational levels of the core-hole states. In Nc photoionization, the shape resonance from the bending-excited level was found to be shifted to the lower photon energy side and to become narrower than that from the ground vibrational level. In Nt photoionization from the bending-excited level, the downward shift of the resonance is more significant than that in Nc ionization. These experimental findings are qualitatively consistent with theoretical predictions and suggest that the shape resonance associated with the Nt core hole is more sensitive to the bending angle of the initial state than is the shape resonance associated with the Nc core hole. The asymmetry parameters for photoionization from the bending-excited level, however, showed almost the same behavior as those from the ground vibrational level for both K-shell photoionization channels and in the photon energy range studied here.

Long carbon-chain molecules were searched for toward the low-mass star-forming region L1527, which is a prototypical source of warm carbon-chain chemistry (WCCC), using the 100 m Green Bank Telescope. Long carbon-chain molecules, C7H ((2)Pi(1/2)), C6H ((2)Pi(3/2) and (2)Pi(1/2)), CH3C4H, and C6H2 (cumulene carbene, CCCCCCH2), and cyclic species of C3H and C3H2O were detected. In particular, C7H was detected for the first time in molecular clouds. The column density of C7H is determined to be 6 x 10(10) cm(-2). The column densities of the carbon-chain molecules including CH3C4H and C6H in L1527 relative to those in the starless dark cloud Taurus Molecular Cloud-1 Cyanopolyyne Peak (TMC-1 CP) tend to be systematically lower for long carbon-chain lengths. However, the column densities of C7H and C6H2 do not follow this trend and are found to be relatively abundant in L1527. This result implies that these long carbon-chain molecules are remnants of the cold starless phase. The results-that both the remnants and WCCC products are observed toward L1527-are consistent with the suggestion that the protostar can also be born in the parent core at a relatively early stage in the chemical evolution.

The spectroscopic constants of s-trans-(E)-2-methyl-2-propenal oxime (methacryl-aldehyde oxime) of normal, H2C=C(CH3)-CH=NOH, and its deuterated species, H2C=C(CH3)-CH=NOD, were determined by observing their microwave spectra in the frequency range of 8 to 40 GHz in the ground vibrational state. The rotational constants were A = 8321.38(82), B = 2076.09(1), and C = 1678.60(1) MHz for normal species and A = 8283.7(16), B = 1998.63(2), and C = 1626.21(2) MHz for deuterated species, respectively. The inertial defects (Delta I = I-c - I-a - I-b) of normal and deuterated species were determined to be -3.09(2) and -3.10(3) u angstrom(2), respectively. The dipole moments were determined as mu(a) = 0.53(2), mu(b) = 0.27(2), and mu(total) = 0.60(5) D. The N-14 nuclear quadrupole coupling constants were determined as chi(aa) = 3.62(12), chi(bb) = 5.1(14), and chi(cc) = 1.48(26) MHz. The comparison of the observed spectroscopic parameters with the calculated ones led to the conclusion that the assigned spectrum was due to s-trans-(E) form. The r(s) coordinates of the hydrogen atom in a hydroxyl group were determined and the OH bond was found to be at the trans position with respect to the C=N double bond. The structural parameters of r(C-2-C-3), r(C-2-C-6), &lt; C2C3N and &lt; C6C2C3, for s-trans-syn form were adjusted to the four observed rotational constants (B and C). The observed rotational constants for s-trans-(E) form were in good agreement with those calculated using the MP2/6-31 G (d,p) level of theory. (C) 2017 Elsevier Inc. All rights reserved.

Using the Green Bank 100 m telescope and the Nobeyama 45 m telescope, we have observed the rotational emission lines of the three C-13 isotopic species of HC3N in the 3 and 7 mm bands toward the low-mass star-forming region L1527 in order to explore their anomalous C-12/C-13 ratios. The column densities of the C-13 isotopic species are derived from the intensities of the J = 5-4 lines observed at high signal-to-noise ratios. The abundance ratios are determined to be 1.00: 1.01 +/- 0.02: 1.35 +/- 0.03: 86.4 +/- 1.6 for [(HCCCN)-C-13]:[(HCCCN)-C-13]:[(HCCCN)-C-13]: [HCCCN], where the errors represent one standard deviation. The ratios are very similar to those reported for the starless cloud Taurus Molecular Cloud-1 Cyanopolyyne Peak (TMC-1 CP). These ratios cannot be explained by thermal equilibrium, but likely reflect the production pathways of this molecule. We have shown the equality of the abundances of (HCCCN)-C-13 and (HCCCN)-C-13 at a high-confidence level, which supports the production pathways of HC3N via C2H2 and C2H2+. The average C-12/C-13 ratio for HC3N is 77 +/- 4, which may be only slightly higher than the elemental C-12/C-13 ratio. Dilution of the C-13 isotope in HC3N is not as significant as that in CCH or c-C3H2. We have also simultaneously observed the DCCCN and HCCC15 N lines and derived the isotope ratios [DCCCN]/[HCCCN] = 0.0370 +/- 0.0007 and [HCCCN]/[(HCCCN)-N-15] = 338 +/- 12.

This work demonstrates that electron correlation can have a strong effect on the radiative lifetime of atoms. We report measurements of the radiative lifetimes of inner-valence hole states, the 3s3p(6) S-2(1/2) state of Ar+ and the 2s2p(6) S-2(1/2) state of Ne+ by using the time-correlated single photon counting technique combined with photoionization by synchrotron radiation. Theoretical calculations utilizing the multi-configuration Dirac-Fock method agreed well with the experimental results. In particular, the radiative lifetime was found to depend very sensitively on the mixing of valence excited state configurations. While the Ne-1 2s2p(6) S-2(1/2) state only has relatively weak inter-shell correlation, Ar+ 3s3p(6) S-2(1/2) state has strong intra-shell correlation within the M-shell. This intra-shell correlation enhances configuration mixing and causes the radiative lifetime of the Ar+ 3s3p(6) S-2(1/2) state to become very much longer than that of the Ne+ 2s2p(6) S-2(1/2) state.

The molecular structure of chloropropanone oxime [ClCH2C(CH3)=NOH] has been determined by gas electron diffraction (GED), microwave spectroscopy (MW) and quantum chemical calculations. Potential energy curves for the internal rotation of CH2Cl group in (E)- and (Z)-isomers as well as the optimized geometries and force constants for four conformations have been calculated by the quantum chemical calculations. Combined data analysis of the GED and MW data revealed the conformational mixture of 68(4) % (E)-anticlinal and 32 % (Z)-synclinal conformers. The principal values of geometrical parameters of the E-anticlinal conformer are: r (g)(ClH2C-C) = 1.499(2) , r (g)(C-CH3) = 1.503(2) , r (g)(C=N) = 1.276(4) , r (g)(C-Cl) = 1.805(3) , r (g)(N-O) = 1.398(4) , a C-alpha-C=N = 113.2(16)A degrees, a C-alpha-C-Cl = 111.1A degrees(5), a alpha H3C-C=N = 127.0A degrees(13), I center dot(NCCCl) = 121.1A degrees(21). Numbers in parentheses are three times standard deviations of the data fit.

The Xe (N5O2,3O2,3) Auger electron spectra originating from 4d−1 5/2 inner-shell photoionization were measured, with photon energy tuned close to the ionization threshold. As the photon energy approaches the threshold from above the 4d−1 5/2 photoionization threshold, Rydberg series structures are formed within the Auger electron peak by the recapture of the photoelectron into<br /> high-lying ion orbitals. They emerge in the tail on the higher energy side of the post–collision interaction (PCI) profile of the Auger electron. Discrete Rydberg peaks replace the continuous PCI tail and gradually form a series with intensity distribution emulating the intensity profile of the continuous tail. Structures due to the Xe+5p4 (1S0, 1D2, 3P2,1,0) ml series were observed and assigned.

The molecular structure of methyl trifluoroacetate (CF3COOCH3) has been determined by gas electron diffraction (GED), microwave spectroscopy (MW), and quantum chemical calculations (QC). QC study provides the optimized geometries and force constants of the molecule. They were used to estimate the structural model for GED study and to calculate the vibrational corrections for GED and MW data. In addition, potential energy curves for the internal rotations of CF3 and CH3 groups have been calculated for anti (dihedral angle of α(CCOC) is 180°) and syn (α(CCOC) = 0°) conformers of methyl trifluoroacetate. Both the GED and MW data revealed the existence of the anti conformer. Molecular constants determined by MW are A0 = 3613.4(3) MHz, B0 = 1521.146(8) MHz, C0 = 1332.264(9) MHz, δJ = 0.09(2) kHz, and δJK = 0.23(6) kHz. The GED data were well-reproduced by the analysis in which a large-amplitude motion of the CF3 group was taken into account. The barrier of the internal rotation of the CF3 group was determined to be V3 = 2.3(4) kJmol-1, where V3 is the potential coefficient of the assumed potential function, V(ø) = (V3/2)(1 - cos3ø), and ø is a rotational angle for the CF3 group. The values of geometrical parameters (re structure) of the anti conformer of CF3COOCH3 are r((O=)C-O) = 1.326(6) Å, r(O-CH3) = 1.421(4) Å, r(C-Hin-plane) = 1.083(14) Å, r(C-Hout-of-plane) = 1.087(14) Å, r(C=O) = 1.190(7) Å, r(C-C) = 1.533(4) Å, r(C-Fin-plane) = 1.319(4) Å, r(C-Fout-of-plane) = 1.320(6) Å, -COC = 116.3(5)°, -OCHin-plane = 105.2° (fixed), -OCHout-of-plane = 110.0° (fixed), -O=CC = 123.7° (fixed), -O-CC = 111.2(5)°, -OCO = 125.2(5)°, -CCF = 110.1(3)°, and OCCF (out-of-plane dihedral angles) = ± 121.5(1)°. Numbers in parentheses are three times the standard deviations of the data fit.

The molecular structure of methyl trifluoroacetate (CF3COOCH3) has been determined by gas electron diffraction (GED), microwave spectroscopy (MW), and quantum chemical calculations (QC). QC study provides the optimized geometries and force constants of the molecule. They were used to estimate the structural model for GED study and to calculate the vibrational corrections for GED and MW data. In addition, potential energy curves for the internal rotations of CF3 and CH3 groups have been calculated for anti (dihedral angle of alpha(CCOC) is 180 degrees) and syn (alpha(CCOC) = 0 degrees) conformers of methyl trifluoroacetate. Both the GED and MW data revealed the existence of the anti conformer. Molecular constants determined by MW are A0 = 3613.4(3) MHz, B-0 = 1521.146(8) MHz, C-0 = 1332.264(9) MHz, Delta(J) = 0.09(2) kHz, and Delta(JK) = 0.23(6) kHz. The GED data were well-reproduced by the analysis in which a large-amplitude motion of the CF3 group was taken into account. The barrier of the internal rotation of the CF3 group was determined to be V-3 = 2.3(4) kJ mol(-1), where V-3 is the potential coefficient of the assumed potential function, V(phi) = (V-3/2)(1 cos 3 phi), and phi is a rotational angle for the CF3 group. The values of geometrical parameters (r(e) structure) of the anti conformer of CF3COOCH3 are r((O=)C-O) = 1.326(6) angstrom, r(O-CH3) = 1.421(4) angstrom, r(C-Hin-plane) = 1.083(14) angstrom, r(C-Hout-of-plane) = 1.087(14) angstrom, r(C=O) = 1.190(7) angstrom, r(C-C) = 1.533(4) angstrom, r(C-Fin-plane) = 1.319(4) angstrom, r(C-Fout-of-plane) = 1.320(6) angstrom, angle COC = 116.3(5)degrees, angle OCHin-plane = 105.2 degrees (fixed), angle OCHout-of-plane = 110.0 degrees (fixed), angle O=C-C = 123.7 degrees (fixed), angle O-CC = 111.2(5)degrees, angle OCO = 125.2(5)degrees, angle CCF = 110.1(3)degrees, and OCCF (out-of-plane dihedral angles) = +/- 121.5(1)degrees. Numbers in parentheses are three times the standard deviations of the data fit.

The rotational spectra of AgCCH and AuCCH were measured using Fourier-transform microwave (FTMW) and source-modulated millimeter-wave spectrometers. For the FTMW measurements, AgCCH and AuCCH were generated in supersonic jets using the pulse-discharge reaction of laser-ablated metal atoms with HCCH diluted with Ar. For the millimeter-wave measurements, these molecules were generated in a free-space cell by sputtering of metal sheets. Rotational transitions were measured for 107AgCCH, 109AgCCH, 107AgCCD, 109AgCCD, AuCCH, and AuCCD. The r0 structures of both molecules were obtained from the rotational constants. The quadrupole parameters of the Au and D nuclei were compared with those of other metal monoacetylides.

To clarify the authenticity of a recently proposed identification of H2CCC (linear-C3H2) as a diffuse interstellar band (DIB) carrier, we searched for the rotational transition of H2CCC at a frequency of 103 GHz toward HD 183143 using the 45 m telescope at the Nobeyama Radio Observatory. Although rms noise levels of 32 mK in the antenna temperature were achieved, detection of H2CCC was unsuccessful, producing a 3 sigma upper limit corresponding to a column density of 2.0 x 10(13) cm(-2). The upper limit indicates that the contribution of H2CCC to the DIB at 5450 angstrom is less than 1/25; thus, it is unlikely that the laboratory bands of the (BB1)-B-1-X(1)A(1) transition of H2CCC and the DIBs at 5450 angstrom (and also 4881 angstrom) toward HD 183143 are related.

To clarify the authenticity of a recently proposed identification of H 2CCC (linear-C3H2) as a diffuse interstellar band (DIB) carrier, we searched for the rotational transition of H 2CCC at a frequency of 103GHz toward HD183143 using the 45m telescope at the Nobeyama Radio Observatory. Although rms noise levels of 32mK in the antenna temperature were achieved, detection of H2CCC was unsuccessful, producing a 3σ upper limit corresponding to a column density of 2.0× 1013cm-2. The upper limit indicates that the contribution of H2CCC to the DIB at 5450 Å is less than 1/25 thus, it is unlikely that the laboratory bands of the B 1 B 1-X 1 A 1 transition of H2CCC and the DIBs at 5450 Å (and also 4881 Å) toward HD183143 are related. © 2012. The American Astronomical Society. All rights reserved..

The molecular structure of 1,1-dicyclopropylethene, c-(C3H5)(2)C=CH2, has been determined by gas electron diffraction (GED) and ab initio calculations. The potential energy surface as a function of the two torsional angles was calculated to examine the conformation of the molecule. The structural model for the GED data analysis was constructed using ab initio calculations at the MP2(full)/aug-cc-pVTZ level of theory. The conformational mixture at about 293 K was determined to be 36(14)5 for the trans-gauche form with C, symmetry and 64(14)5 for the gauche-gauche form (mixture of the gauche-gauche form with C-2 symmetry (38(27)%) and the gauche-gauche' form with C-5 symmetry (26%)). The uncertainty of the gauche-gauche form with C-2 symmetry was estimated by the Hamilton R-factor ratio test. The present result is in agreement with that reported in a previous GED study (Traetteberg et al. J. Mol. Struct. 485-486 (1999) 73). The conformational abundances determined by GED are different from those in liquid xenon determined by a vibrational spectroscopic study (Dung et al., J. Phys. Chem. A. 109 (2005) 1650). (C) 2012 Elsevier B.V. All rights reserved.

We report a sensitive search for the rotational transitions of the carbon-chain alcohol HC4OH in the frequency range 21.2-46.7 GHz in the star-forming region L1527 and the dark cloud TMC-1. The motivation was laboratory detection of HC4OH by microwave spectroscopy. Despite achieving rms noise levels of several millikelvin in the antenna temperature using the 45 m telescope at Nobeyama Radio Observatory, the detection was not successful, leading to 3 sigma upper limits corresponding to the column densities of 2.0 x 10(12) and 5.6 x 10(12) cm(-2) in L1527 and TMC-1, respectively. These upper limits indicate that [HC4OH]/[HC5N] ratios are less than 0.3 and 0.1 in L1527 and TMC-1, respectively, where HC5N is an HC4-chain cyanide and HC4OH is a hydroxide. These ratios suggest that the cyano carbon-chain molecule dominates the hydroxyl carbon-chain molecule in L1527 and TMC-1. This is contrary to the case of saturated compounds in hot cores, e. g., CH3OH and CH3CN, and can be a chemical feature of carbon-chain molecules in L1527 and TMC-1. In addition, the column densities of the " unsubstituted" carbon-chain molecule C4H and the sulfur-bearing molecules SO and HCS+ were determined from detected lines in L1527.

High-resolution N 1s and O 1s photoelectron spectra (PES) of NO are presented together with spectra of the subsequent Auger decay. The PES are analyzed by taking spin-orbit splitting of the (2)Pi ground state into account providing detailed information on equilibrium distances, vibrational energies, and lifetime widths of the core-ionized states. In the Auger electron spectra (AES) transitions to five metastable dicationic final states are observed, with two of them previously unobserved. A Franck-Condon analysis of the vibrational progressions belonging to these transitions provides detailed information on the potential-energy curves of the dicationic final states as well as on the relative Auger rates. The present calculations of the potential-energy curves of NO2+ agree well with the experimental results and allow an assignment of the two hitherto unresolved Auger transitions to excited states of NO2+, C-2 Sigma(+) and c(4)Pi.

Recoil-induced rotational excitation accompanying photoionization has been measured for the X, A, and B states of N-2(+) and CO+ over a range of photon energies from 60 to 900 eV. The mean recoil excitation increases linearly with the kinetic energy of the photoelectron, with slopes ranging from 0.73 x 10(-5) to 1.40 x 10(-5). These slopes are generally (but not completely) in accord with a simple model that treats the electrons as if they were emitted from isolated atoms. This treatment takes into account the atom from which the electron is emitted, the molecular-frame angular distribution of the electron, and the dependence of the photoelectron cross section on photon energy, on atomic identity, and on the type of atomic orbital from which the electron is ejected. These measurements thus provide a tool for investigating the atomic orbital composition of the molecular orbitals. Additional insight into this composition is obtained from the relative intensities of the various photolines in the spectrum and their variation with photon energy. Although there are some discrepancies between the predictions of the model and the observations, many of these can be understood qualitatively from a comparison of atomic and molecular wavefunctions. A quantum-mechanical treatment of recoil-induced excitation predicts an oscillatory variation with photon energy of the excitation. However, the predicted oscillations are small compared with the uncertainties in the data, and, as a result, the currently available results cannot provide confirmation of the quantum-mechanical theory. (C) 2010 American Institute of Physics. [doi:10.1063/1.3503658]

The gas-phase structure of (E)-benzaldehyde oxime (C(6)H(5)-CH = NOH), has been determined by gas-phase electron diffraction (CED), microwave spectroscopy (MW) and quantum-chemical calculations. Two sets of the data analyses were performed. One was GED + MW data analysis with a small-amplitude vibrational model. A planar conformation for this molecule was adopted in the analysis. Another was GED data analysis of a large-amplitude motion of the C-C torsion. The potential minimum was located on the planar conformation of this molecule. Above two sets of the data analyses were led to the one consistent result that showed good agreement between the experimental and calculated molecular intensities. (C) 2010 Elsevier B.V. All rights reserved.

The microwave spectra of two isotopic species of acetyl isocyanate, (CH3C)-C-13(O)NCO and CD3C(O)NCO, were observed in order to determine the r(o) structure and confirmation of the molecular conformation. These isotopic species were prepared by reacting acetyl-2-C-13-Chloride of acetyl-d(3) chloride with sliver cyanate. The rotational spectra of A-level in 26.5-60.0 GHz region have been observed by Stark-modulated microwave spectrometer. Some absorption lines in E-level were observed in (CH3C)-C-13(O)NCO. The rotational constants in the ground vibrational state were determined to be A = 10654.8(18), B = 2177.32(2), and C = 1827.65(2) MHz for (CH3C)-C-13(O)NCO, and A = 9713.90(6), B = 2042.04(2). and C = 1722.78(2) MHz for CD3C(O)NCO, respectively. The values of Delta I (= I-c - I-a - I-b) of the C-13 species (-3.024(13) u angstrom(2)) and the d(3) species (-6.163(3) u angstrom(2)) indicate that the molecule has C-s symmetry. The r(s) coordinates of the carbon atom in the methyl group were determined to be vertical bar a vertical bar = 2.183(3). vertical bar b vertical bar = 0.706(9). and vertical bar c vertical bar = 0.080(87) angstrom. The determined coordinates were in agreement with those calculated for the cis form, in which the carbonyl group is eclipsed by the NCO group. The six structural parameters of the cis form were adjusted by fitting to the observed rotational constants. The observed rotational constants of the cis form were in better agreement with those calculated using the QCISD/6-31G (d, p) level rather than those calculated using the MP2/6-31G (d, p) level. The barrier of internal rotation of the methyl group was determined as 4.283(16) kJ mol(-1) in (CH3C)-C-13(O)NCO. The structural tendencies and the relationship between angle RNC and N-14 quadrupole coupling constants (chi(cc)) were discussed. (C) 2009 Elsevier Inc. All rights reserved.

The microwave spectra of monochloroamine (NH2Cl) and its isotopic species have been observed by Cazzoli et al. [G. Cazzoli, D.C. Lister, P.G. Favero, J. Mol. Spectrosc. 42 (1972) 286-295; G. Cazzoli, D.G. Lister, J. Mal. Spectrosc. 45 (1973) 467-474]. We observed microwave spectra of four isotopic species of (NHDCl)-N-14-Cl-35, (NHDCl)-N-14-Cl-37, (ND2Cl)-N-14-Cl-35, and (ND2Cl)-N-14-Cl-37 produced by the direct reaction of ammonia gas-d(3) or ammonium hydroxide-d(5) with N-chlorosuccinimide. The microwave spectra of NHDCl (d(1)-species) and ND2Cl (d(2)-species) were observed in the frequency range from 8.0 to 60 GHz. The inversion splitting (Delta E-o) of (NHDCl)-N-14-Cl-35 and (NHDCl)-N-14-Cl-37 in the ground vibrational state are shown to be 11.46(15) and 11.44(15) MHz for K-a = 0 &lt;- 1, and 10.49(15) and 10.26(15) MHz for K-a = 1 &lt;- 2, respectively. However, the inversion splitting of the d(2)-species could not be observed in our spectrometer. Only small J and K-dependence of the inversion splitting of d(1)-species was observed. The rotational constants of (NHDCl)-N-14-Cl-35 were determined to be A = 187895.44(18), B = 13353.343(15) and C = 12859.794(15) MHz for the 0(+) &lt;- 0(-) state, which means the transition from the lower inversion level to the upper one, and A = 187918.52(18), B = 13353.345(15) and C = 12859.798(14) MHz for the 0(-) &lt;- 0(+) state. The rotational and centrifugal distortion constants of (ND2Cl)-N-14-Cl-35 were determined to be A = 141030.885(72), B = 12594.481(6) and C = 12055.356(6) MHz, and Delta(J) = 18.342(23), Delta(JK) = 318.15(56). Delta(K) = 2219.3 (fixed), delta(J) = 0.8717(17) and delta(K) = 157.78(61) kHz. The values of the planar moments P-bb = (I-b - I-a - I-c)/2, of (NDCl)-N-14-Cl-35 and (ND2Cl)-N-14-Cl-37 were found to be 2.68898(2) and 2.68890(2) u angstrom(2), respectively, which are about twice its large as those of normal species (P-bb = 1.3548(6) and 1.3544(16) u angstrom(2), respectively). It was found that the bond length of r(N-Cl) of NH2Cl was longer than that of Cl-NCO by 0.045(12) angstrom, and was almost the same as that of CH2=N-Cl, while it was much shorter than those of Cl-NO2 and Cl-NO, by 0.092(6) and 0.227(6) angstrom, respectively. (C) 2008 Elsevier Inc. All rights reserved.

The rotational spectra of HC4OH and its deuterated species have been detected in the 17-39 GHz region by microwave spectroscopy. The spectra were generated after pyrolysis of 2-butynol at 830 degrees C; a deuteration reaction to produce DC4OH and HC4OD was caused by mixing the 2-butynol with deuterated water vapor. The rotational constants B and C were precisely determined for HC4OH and the rotational constant was determined (B + C)/2 for DC4OH and for HC4OD. With these rotational constants, the entire radio spectrum of HC4OH can be accurately estimated to better than 0.42 MHz accuracy at frequencies up to 51.1 GHz. These transition frequencies should be of great use for astronomical identification of this molecule.

The microwave spectra of two conformers of (E)-2-methylpropanal oxime ((CH3)(2)CH - CH=NOH) and its deuterated species ((CH3)(2)CH - CH=NOD) were observed in the frequency range from 8 to 40 GHz. The absorption lines in the ground and excited vibrational states were assigned. The rotational constants of normal species in the ground vibrational state were determined to be A=7343.5(25), B=1847.20(2), and C=1607.29(2) MHz for (E)-sp isomer and A=7073.15(84), B=2006.01(1), and C = 1686.62(1) MHz for (E)-ac isomer. The planar moments (P-bb = (I-c + I-a - I-b)/2) of the normal and deuterated species were determined to be 54.829(15) and 54.829(8) u angstrom(2) for the (E)-sp, and 59.578(6) and 59.768(7) u angstrom(2) for the (E)-ac, respectively. The P-bb values of the (E)-sp of normal and deuterated species suggest that the (E)-sp has C-s symmetry. The r(s) coordinates of the hydrogen atoms of the hydroxyl group were determined for the (E)-sp and the (E)-ac. They indicated that their OH bonds took trans positions with respect to the C=N double bond. The four and six structural parameters were adjusted by fitting to the rotational constants of the (E)-sp and (E)-ac, respectively. The observed rotational constants (B and Q of the (E)-sp and the (E)-ac isomers were in better agreement with those calculated using the MP2/6-31++G(d, p) level than with those calculated using the MP2/6-31G(d, p) level. (c) 2008 Published by Elsevier B.V.

The microwave spectra of cyclohexanone oxime and d(1) (=NOD) and d(4)(2,2,6,6-d(4)) derivatives were observed in the frequency range from 8 to 40 GHz in the ground and excited vibrational states. The rotational constants were determined to be A = 3799.844(48), B = 1513.7912(23), and C = 1189.6118(29) MHz for normal species, A = 3791.835(88), B = 1461.0324(47), and C = 1157.5653(53) MHz for d(1) species, and A = 3364.141(49), B = 1487.9551(34), and C = 1154.0965(44) MHz for d(4) species in the ground vibrational state. The planar moments, P-bb (P-bb =(I-c + I-a - I-b)/(2)) of normal, d(1), and d(4) species were determined to be 111.9885(26), 111.9817(46), and 124.2394(49) u angstrom(2), respectively. The almost same values of P-bb of normal and d(1) species suggest that the hydroxyl hydrogen atom is very close to the a-c plane. From the r(s) coordinates of the hydroxyl hydrogen atom, the OH bond was found to be at the trans position with respect to the C=N double bond. The conformation of cyclohexanone oxime was determined to be chair form by comparing the observed and calculated rotational constants, Delta I, and planar moments, and taking account of the calculated the relative energy difference, Delta E. The structural parameters, the three bond lengths, three bond angles, and three dihedral angles, were adjusted to the nine rotational constants observed. The bond angle of angle C2C1N is much wider than that of angle C6C1N by about 10 degrees. The dihedral angles of angle C1C2C3C4, angle C2C3C4C5, and angle C3C4C5C6 were determined to be 53.3(5), -57.2(5), and 57.2(5)degrees. Two vibrational modes were assigned to the ring-bending and ring-twisting ones, which are almost harmonic up to v = 3. (C) 2007 Elsevier Inc. All rights reserved.

The microwave spectra of 2-cyclohexen-1-one oxime and its deuterated (=NOD), species were observed in the frequency range from 8 to 40 GHz in the ground vibrational state. The rotational constants were determined to be A = 4399.83 (12), B = 1507.832(4), and C = 1166.821(6) MHz For normal species and A = 4400.10(34), B = 1454.06(2), and C = 1134.38 (1) MHz for deuterated species. The inertial defects (Delta I = I-c - I-n - I-b) of normal and deuterated species were determined to be - 16.907 (6) and - 16.909 (18) u angstrom(2), respectively. The Delta I value suggests a plausible molecular structure in which the NOH group and five carbon atoms of the cyclohexene ring are coplanar, but one of the carbon atoms deviates from this plane. The anti form was determined by comparing the observed and calculated rotational constants, Delta I and Delta E (relative energy). From the r(s) coordinates of the hydroxyl hydrogen atom, the OH bond was found to be at the trans position with respect to the C=N double bond. The structural parameters of the two bond lengths and three bond angles of anti form were adjusted to the six rotational constants observed. It was found that the bond angle of angle C(H-2)CN is much wider than that of angle C(H)CN by about 10 degrees. The rotational constants (B and C) of anti form calculated using MP2/6-31G (d, p) level were in good agreement with those observed. (C) 2006 Elsevier Inc. All rights reserved.

The spectroscopic constants of s-trans-(E)- and s-trans-(Z)-crotonaldehyde oxime (Fig. 1) of normal, CH3CH=CH-CH=NOH, and deuterated, CH,CH=CH-CH=NOD, species were observed in the frequency range of 8-40 GHz in the ground vibrational state. The rotational constants of two isomers of normal species were determined to be A = 27,093(15 1), B = 1270.656(8), and C = 1223.288(8) MHz for s-trans-(E) form and A = 12,239(19), B = 1587.49(2), and C= 1417.80(2) MHz for s-trans-(Z) form. The inertial defects (Delta I= I-c-I-a-I-b) of normal and deuterated species were determined to be - 3.25(11) and - 3.24(20) u angstrom(2) for s-trans-(E) form, and - 3.191(73) and - 3.180(36) u angstrom(2) for s-trans-(Z) form, respectively. From the r(s) coordinates of the hydroxyl hydrogen atom determined for s-trans-(E) and s-trans-(Z) forms, their OH bonds were concluded to be at the trans position with respect to the C=N double bond. For s-trans-(E) form, the C-3-C-4 torsional excited vibrational states were observed up to v = 3. The vibrational frequency was found to be 90(40) cm - 1 from the relative intensity measurement. The vibrational mode was nearly harmonic. The structural parameters of r(C-4=N), r(C-3-C-4), angle C3C4N and angle-C4NO for s-trans-(E) and s-trans-(Z) forms were adjusted separately to their rotational constants observed. It was found that the bond angle of angle C3C4N in s-trans-(Z) form are much wider than that in s-trans-(E) form by about 10 degrees. The rotational constants observed for s-trans-(E) and s-trans-(Z) forms were consistent with those calculated using MP2/6-31G(d,p) rather than 6-311 + +G(d,p) basis sets, and those (B and C) calculated for s-trans-(E) using MP2/6-31G(d,p) were in excellent agreement with those observed. (c) 2005 Elsevier B.V. All rights reserved.

The C K-shell photoelectron mainline of C2H2 molecules have been measured at photon energies 295-350 eV. The gerade and ungerade symmetries of the core-ionized states, 1 sigma(g) and 1 sigma(u), are resolved. Resonance enhancement is found only in the log photoionization cross-section and assigned to the sigma(u)(*) shape resonance. The photoelectron asymmetry parameter takes a minimum value at the shape resonance energy. The shape resonance energy decreases with increase in the vibrational quantum number. No correlational shape resonance appears in the 1 sigma(u) photoionization channel, suggesting that the channel coupling is negligible. (c) 2006 Elsevier B.V. All rights reserved.

The microwave spectra of cyclopentanone oxime (C5H8 = NOH) and its deuterated Species (C5H8 = NOD) were observed in the frequency region from 9 to 40 GHz. Only a-type R-branch transitions were assigned in the vibrational ground and excited states. The rotational constants of normal species were determined to be A = 5870.80(33), B = 1917.021(8), and C = 1526.784(8) MHz in the vibrational ground state, and A = 5870.16(43), B = 1842.707(9), and C = 1479.40](9) MHz for deuterated species. The dipole moments were determined as u(a) = 0. 80(10), mu(b) = 0.20(10), and mu(c) = 0.40(10) D. The ring-puckering vibrational states were observed up to v = 6. The vibrational mode was nearly harmonic. The fundamental frequency of the ring-puckering mode was found to be 70(20) cm(-1). The molecular structure of cyclopentatione oxime was determined to be a twisted configuration by comparing the observed and calculated rotational constants, planar moment of inertia, P-cc, and r(s) coordinates of the hydroxyl hydrogen atom. On the molecular geometry, the bond angle, ZC(2)C(1)N(6) (Fig. 1), is larger than angle C5C1N6 by ca. 6 degrees, because of the steric repulsion between the methylene group of C-2 atom and hydroxyl group. (c) 2004 Elsevier Inc. All rights reserved.

Microwave spectra of six isotopic species of (E)- and (Z)-acetaldehyde oxime (CH3CD=NOH, CH3CH=(NOH)-N-15, (CH3CH)-C-13=NOH, (CH3CH)-C-13-C-13=NOH, CD3CH=NOH, and CD3CD=NOH) were observed in the frequency range of 26.0-40.0 GHz. Adding to normal species and CH3CH=NOD, the r(s) coordinates of H-1, N, C-1, C-2, and H-3 atoms (refer to Fig. 1) of (E) and (Z) isomers in A-state were calculated using Kraitchman's equation. The structural parameters, three bond lengths and three bond angles of (E)- and (Z)-acetaldehyde oxime in A-state were determined. The structural parameters obtained are as follows: for E isomer. r(C-1=N): 1.265(15) Angstrom, r(C-1-C-2): 1.510(11)Angstrom, r(C-1-H-1): 1.110(9) Angstrom, angleC(2)C(1)N: 117.7(8)degrees, angleH(1)C(1)N: 118.1(5)degrees, and angleC(2)C(1)H(1): 124.2(7)degrees, and for Z isomer, r(C-1=N): 1-275(4)Angstrom, r(C-1-C-2): 1.510(14) Angstrom, r(C-1-H-1): 1.091(8) Angstrom, angleC(2)C(1)N: 124.3(7)degrees, angleH(1)C(1)N: 113.6(5)degrees, and angleC(2)C(1)H(1): 122.1(7)degrees. The bond angle angleC(2)C(1)N in Z isomer is much larger than that of (E) isomer. because of the steric repulsion between the methyl and hydroxyl groups in (Z) isomer. The steric repulsion may be related to the low barrier height (V-3) of the methyl group in Z isomer. (C) 2004 Elsevier B.V. All rights reserved.

The spectroscopic constants of s-trans (E)-acrylaldehyde oxime of normal, CH2=CH-CH=NOH, and deuterated, CH2=CH-CH=NOD, species were refined by adding a-type R-branch transitions observed in the frequency range of 34-40 GHz in the ground vibrational state. For s-trans (Z) form, the spectroscopic constants of normal species were refined by refitting the reported frequencies with four b-type Q-branch transitions and those of deuterated species were determined by the least-squares fitting of the observed a-type R-branch transitions in the ground vibrational state. The spectroscopic constants of two isomers of normal species were also determined in the vibrationally excited states. The inertial defects (DeltaI = I-c - I-a - I-b) of normal and deuterated species were determined to be -0.042(24) and -0.064(17) u Angstrom(2) for s-trans (E)-1 form, and -0.0536(8) and -0.063(11) u Angstrom(2) for s-trans (Z)-1 form, respectively. From the r(s) coordinates of the hydroxyl hydrogen atom determined for s-trans (Z)-1 form, its OH bond was concluded to be at the trans position with respect to the C=N double bond. The dipole moments of deuterated species of s-trans (E)-1 form and those of normal and deuterated species of s-trans (Z)-1 form were determined. The structural parameters of r(C-2-C-3), &lt;C1C2C3, &lt;C2C3N, and &lt;C3NO for s-trans (E)-1 and s-trans (Z)-1 forms were adjusted separately using to their rotational constants observed. It was found that the bond angle of &lt;C2C3N in s-trans (Z)-1 form are much wider than that in s-trans (E)-1 form by about 10degrees. The difference between the observed and calculated (using MP2/6-311++G (d,p) level) rotational constants of s-trans (Z)-1 form was larger than that of s-trans (E)-1 form. (C) 2003 Elsevier Inc. All rights reserved.

The molecular structure of 1,3-dichloropropanone (ClCH2)(2)C=O, was determined by gas-phase electron diffraction (GED), augmented by ab initio MO calculations. The nozzle temperature in the GED experiment was about 365 K. Vibrational amplitudes and shrinkage corrections for the data analysis of GED were calculated from the harmonic force constants given by normal coordinate analysis. The C-C torsions were treated as large-amplitude vibrations in the data analyses. The potential function for the C-C torsional motion was approximated as V(phi(1), phi(2)) = (V-1/2)(1 - cos(phi1)) + (V-1/2)(1 - cos(phi(2))) + (V-3/2)(1 - cos(3phi(1))) + (V-3/2)(1 - cos(3(phi(2))) + V-11 sin(phi(1))sin(phi(2)) + V'(11) cos(phi(1))cos(phi(2)), where 0 1 and 4)2 are the dihedral angles of ClCCO for the two ClCH2 groups. The values of V-1, V-3, V-11 and V'(11) were determined to be - 3.6, 4.8, - 5.5, and 2.8 kJ mol(-1), respectively. It was found that the anticlinal-anticlinal (ac-ac) conformer was dominant, with a small population of the anticlinal-synperiplanar (ac-sp) conformer present. The ac-ac conformer possesses C-2 symmetry, where phi(1) and phi(2) are both 116degrees and the ac-sp conformer has C, symmetry with the ClCCO dihedral angles of 128 and 12degrees. The principal bond distances and angles (rg (Angstrom) and angle(alpha) (degrees)) of the ac-ac conformer are: r(C-C) = 1.526(3); r(C=O) = 1.210(2); r(C-Cl) = 1.789(1); angleCCO = 121.0(4); angleCCCl = 110.2(4). The values in parentheses are three times the standard deviations. The ac-ac conformer is much more abundant than the other conformers in the gas phase, although the synperiplanar-synperiplanar conformer, where the two ClCCO angles are nearly equal to zero, is dominant in the crystal. (C) 2002 Elsevier Science B.V. All rights reserved.

syn-1-Chloro-2-nitrosopropene (ClCH=C(CH3)-NO) was generated by the vacuum solid-gas chemical reaction of 1,1-dichloro-2-(hydroxyimino)propane with anhydrous potassium carbonate. The product was identified by observing the microwave spectrum observed in the frequency range from 20 to 60 GHz. The rotational constants (MHz) for A symmetric species were determined to be A = 8531(4), B = 1470.00(2), and C = 1263.56(2) for syn- (ClCH)-Cl-35=C(CH3)- (NO)-N-14 (Cl-35 species), A = 8517(10), B = 1431.44(5), and C = 1234.97(6) for syn-(ClCH)-Cl-37=C(CH3)- (NO)-N-14 (Cl-37 species), and A = 8451(8), B = 1458.03(7), and C = 1252.87(6) for syn- (ClCH)-Cl-35=C(CH3)- (NO)-N-15 (N-15 species) in the ground vibrational states. The values of planar moment (P-cc = (I-a + I-b - I)/2) obtained for Cl-35, Cl-37, and N-15 isotopic species were 1.53(2), 1.58(5), and 1.52(5) uAngstrom(2), respectively. Those values suggest that the chlorine and nitrogen atoms lie in or are close to the a-b inertial axis plane of the molecule, and show that only two hydrogen atoms are located symmetrically out of the molecular symmetry plane. The reaction product was concluded to be syn-1-chloro-2-nitrosopropene by comparing the observed and calculated rotational constants, K (Ray's asymmetry parameter), and r(s) coordinates of the chlorine and nitrogen atoms. Five structural parameters: r(C-CH3), r(C-N), angleCl-C=C, angleC=C-C, and angleC=C-N, were determined by least-squares fitting, using the six rotational constants (B and C) of the three Cl-35, Cl-37, and N-15 isotopic species. The barrier heights, V-3, to the internal rotation of the methyl group of Cl-35, Cl-37, and N-15 isotopic species in the ground vibrational states were obtained to be 680(30), 680(30), and 687(30) cal/mol (1 cal/mol = 4.184 J/mol). (C) 2002 Elsevier Science B.V. All rights reserved.

The pyrolysis products of CH2=(CH3)-NO (syn form) have been determined by microwave spectroscopy. The pyrolysis products of CH2=(CH3)-NO (syn form) and its N-15 isotopic species were found to be CH2=O CH3CN, and (CH3CN)-N-15. The produce of formaldehyde and methyl cyanide suggests that the C=C and N=O double bonds of CH2=(CH3)-N=O (syn form) were broken. To explain the generation of the two molecules, a four-membered ring molecule (9) as an intermediate, is proposed. The four-membered ring molecule as an intermediate is also supported by ab initio MO calculation. Applying the pyrolysis mechanism obtained for 2-nitrosopropene (syn form) to that of 1,1,2-trichloronitrosoethane, one of its complicated pyrolysis mechanisms was explained. The rotational constants and geometrical parameters of two intermediates, 9 and CH2=CCl-NO (13), were obtained by ab initio MO calculation (MP2/6-31G**) to predict their microwave spectra. (C) 2001 Elsevier Science B.V. All rights reserved.

syn-2-Nitrosopropene was generated, in the gas phase, by chemical reaction of 1-chloro-2-(hydroxyimino)propane with K2CO3 and identified by microwave spectroscopy. The microwave spectrum of the reaction product was observed in the frequency range from 8.0 to 40.0 GHz. The rotational constants (MHz) were determined as A = 8744.09(6), B = 4846.07(2), and C = 3177.84(3) for CH2=C(CH3)-(NO)-N-14 (normal species) and A = 8664.36(5), B = 4822.15(3), and C = 3157.04(3) for CH2=C(CH3)-(NO)-N-15 (N-15 species) in the ground vibrational state. The values of the planar moment (P-cc = (I-a + I-b - I-c)/2) obtained for the normal and N-15 species were 1.525(1) and 1.526(1) u Angstrom (2) respectively. This suggests that the nitrogen atom lies in or is close to the nb inertial plane of the molecule and shows also that only two hydrogen atoms are located symmetrically out of the symmetry plane. The reaction product was determined to be syn-2-nitrosopropene by comparing the observed and calculated rotational constants, kappa (Ray's asymmetry parameter) and r(s) coordinates of the nitrogen atom. The dipole moments (D) were determined to be mu (a) = 2.43(5), mu (b) = 1.12(7), and mu (total) = 2.67(7). The barrier heights of the internal rotation owing to the methyl group of the normal species in the ground and first excited torsional states were determined to be 1750(50) and 1740(50) cal/mol (1 cal/mol = 4.184 J/mol), respectively. The N-14 nuclear quadrupole coupling constants (MHz) were determined to be chi (aa) = 0.25(21), chi (bb) = -7.11(40), and chi (cc) = 6.85(61). Two vibrational excited states were observed and the vibrational frequencies (cm(-1)) of the C-N and C-C torsional modes were determined to be 160(40) and 175(40), respectively. The lifetime of syn-2-nitrosopropene was found to be ca. 2 min in the waveguide cell. (C) 2000 Academic Press.

The pyrolysates of CICH2CH2NCO and ClCH2CH2NCS were investigated by pyrolysis-mass spectrometry and microwave spectroscopy (Py-MS/MW) at 100-900 degrees C. In the mass spectrum of the pyrolysate of CICH2CH2NCO a characteristic ion is seen at mit 69, while in that of ClCH2CH2NCS ions at m/z 59, 62, 64, and 85 are observed. The identification by MW revealed that the ion at m/z 69 is the molecular ion of vinyl isocyanate, while the ion at mit 59 is that of isothiocyanic acid, at m/z 62 and 64 are those of vinyl chloride, and at m/z 85 is that of vinyl isothiocyanate. In spite of the similarity of the two compounds, it was found that the pyrolysis mechanism of CICH2CH2NCS was different from that of ClCH2CH2NCO. The generation of vinyl chloride and isothiocyanic acid from CICH2CH2NCS suggests that the C-N single bond of CICH2CH2NCS may be weaker than that of ClCH2CH2NCO. (C) 2000 Elsevier Science B.V. All rights reserved.

The microwave spectrum of chloropropanone oxime was observed in the frequency range from 26.5 to 40.0 GHz. The rotational constants (A-level) (MHz) were determined as A = 6501.04(15), B = 1464.98(1), and C = 1326.80(1) for (ClCH2C)-Cl-35(CH3)=NOH(Cl-35 species) and A = 6519.5(15), B = 1428.07(1), and C = 1298.00(1) for (ClCH2C)-Cl-37(CH3) = NOH(Cl-37 species) in the ground Vibrational state. The values of Delta I(= I-c-I-b-I-a) obtained for the Cl-35 and Cl-37 species were found to be -41.811(7) and -42.06(2) u Angstrom(2), respectively. The observed rotational constants, Delta I, and r(s)-coordinates of the chlorine atom were in good agreement with those of anticlinal form in E-isomer (E-ac), having the dihedral angle (phi) of ClC1C2N = 116.8 degrees, as shown in Fig. 2. One vibrationally excited state was observed and assigned to the C-1-C-2 torsional mode (80(20) cm(-1)). (C) 2000 Elsevier Science B.V. All rights reserved.

The pyrolysates of 1,1,2-trichloronitrosoethane (CH2Cl-CCl2-NO) have been investigated by pyrolysis-mass spectrometry and microwave spectroscopy (Py-MS/MW). The five pyrolysates were identified to be 1,1-dichloroethene 1, nitrosyl chloride 2, chloroacetylene 3, formaldehyde 6 and cyanogen chloride 7 by microwave spectroscopy. The generation of 3 was verified by the direct reaction of 1 with NOX and Cl* radicals inside a Stark cell. Two radicals were generated by pyrolysis of 2. The observed ionic peaks m/z at 91 and 93 (C2H2ClNO) having the relative intensity of 3:1 were tentatively assigned to 1-chloronitrosoethene (4 or 4') produced by elimination of Cl-2 of the precursor. Two pyrolysis mechanisms of 1,1,2-trichloronitrosoethane were elucidated by judging from these pyrolysates identified. One is that 1 is generated by elimination of 2, and 3 is furthermore produced by reaction of 1 with NO and Cl radicals. The other is that 4 may be generated by elimination of Cl-2 of the precursor and 6 and 7 may be produced by cleavage of four-membered ring molecule 5 produced by intramolecular cyclization of 4. (C) 2000 Elsevier Science B.V. All rights reserved.