Hoshino Masamitsu

We report vibrational excitation functions and angular distributions for electron scattering from the ground vibrational quantum (000), the bending vibrational quantum (010) and the unresolved first bending overtone (020) and symmetric stretch (100) modes of the ground-electronic state in hot (750 K) carbon dioxide (CO2) molecules. The excitation function measurements were carried out at incident electron energies in the range of 1-9 eV, and at the electron scattering angles of 30 degrees, 60 degrees, 90 degrees and 120 degrees.

We present experimental differential cross sections for the elastic scattering of electrons from CF3H and CF3I for scattering angles from 10° or 20° up to 180° at incident electron energies of 5, 10, 20, 30 and 50 eV. We also estimate integral and momentum transfer cross sections with the present measurement of differential cross sections as well as with our previous (Varella et al 2002 Phys. Rev. A 65 022702 for CF 3H Kitajima et al 2002 J. Phys. B: At. Mol. Opt. Phys. 35 3257 for CF3I) differential cross section sets for both molecules. The agreement with the previous results is generally good with a few exceptions. © 2010 IOP Publishing Ltd.

A new type of the experimental set-up for the measurements of the total cross section for collisions between electrons and atoms or molecules at very low collision energies, which are called as Cold Electron Collisions. The key of this set-up is to use the threshold photoelectrons as a source for low-energy electron beam combined with the penetration field method. Total cross sections measurements over the energy range from thermal energy to 12eV with high-energy resolution by this new set-up are presented.

A magnetic field-free slow positron beam apparatus has been developed for the studies of positron scattering from atoms and molecules. It uses electrostatic lens elements and a remoderator in a reflection geometry for the brightness enhancement. The preliminary results of the total cross sections for positron-He scattering in the energy range up to 100 eV are presented.

Differential and integral cross sections for electron-impact excitation of the dipole-allowed C (II)-I-1 and D (1)Sigma(+) electronic states of nitrous oxide have been measured. The differential cross sections were determined by analysis of normalized energy-loss spectra obtained using a crossed-beam apparatus at six electron energies in the range 15-200 eV. Integral cross sections were subsequently derived from these data. The present work was undertaken in order to check both the validity of the only other comprehensive experimental study into these excitation processes [Marinkovic et al., J. Phys. B 32, 1949 (1998)] and to extend the energy range of those data. Agreement with the earlier data, particularly at the lower common energies, was typically found to be fair. In addition, the BEf-scaling approach [Kim, J. Chem. Phys. 126, 064305 (2007)] is used to calculate integral cross sections for the C (II)-I-1 and D (1)Sigma(+) states, from their respective thresholds to 5000 eV. In general, good agreement is found between the experimental integral cross sections and those calculated within the BEf-scaling paradigm, the only exception being at the lowest energies of this study. Finally, optical oscillator strengths, also determined as a part of the present investigations, were found to be in fair accordance with previous corresponding determinations. (C) 2009 American Institute of Physics. [doi: 10.1063/1.3230150]

We present absolute differential cross sections (DCS) for elastic scattering from two benzene derivatives C6 H5 CH3 and C6 H5 CF3. The crossed-beam method was used in conjunction with the relative flow technique using helium as the reference gas to obtain absolute values. Measurements were carried out for scattering angles 15°-130° and impact energies 1.5-200 eV. DCS results for these two molecules were compared to those of C6 H6 from our previous study. We found that (1) these three molecules have DCS with very similar magnitudes and shapes over the energy range 1.5-200 eV, although DCS for C6 H5 CF3 increase steeply toward lower scattering angles due to the dipole moment induced long-range interaction at 1.5 and 4.5 eV, and (2) that the molecular structure of the benzene ring significantly determines the collision dynamics. From the measured DCS, elastic integral cross sections have been calculated. Furthermore, by employing a corrected form of the independent-atom method known as the screen corrected additive rule, DCS calculations have been carried out without any empirical parameter fittings, i.e., in an ab initio nature. Results show that the calculated DCS are in excellent agreement with the experimental values at 50, 100, and 200 eV. © 2009 The American Physical Society.

We present absolute differential cross sections (DCS) for elastic scattering from two benzene derivatives C6H5CH3 and C6H5CF3. The crossed-beam method was used in conjunction with the relative flow technique using helium as the reference gas to obtain absolute values. Measurements were carried out for scattering angles 15 degrees-130 degrees and impact energies 1.5-200 eV. DCS results for these two molecules were compared to those of C6H6 from our previous study. We found that (1) these three molecules have DCS with very similar magnitudes and shapes over the energy range 1.5-200 eV, although DCS for C6H5CF3 increase steeply toward lower scattering angles due to the dipole moment induced long-range interaction at 1.5 and 4.5 eV, and (2) that the molecular structure of the benzene ring significantly determines the collision dynamics. From the measured DCS, elastic integral cross sections have been calculated. Furthermore, by employing a corrected form of the independent-atom method known as the screen corrected additive rule, DCS calculations have been carried out without any empirical parameter fittings, i.e., in an ab initio nature. Results show that the calculated DCS are in excellent agreement with the experimental values at 50, 100, and 200 eV.

Electron and positron cross sections have been investigated experimentally for scattering from benzotrifluoride (C(6)H(5)CF(3)) molecules over the energy range 0.2-1000 eV. The current results have been compared with our previous results for C(6)H(6) molecules. Similar to C(6)H(6), a peak has been observed in electron total cross sections (TCS) centered at 8.0 and a shoulder at about 40 eV. Vibrational excitation cross section experiments were carried out to probe the origin and nature of the 8 eV peak. For positron TCS, a broad peak spanning the region 0.8-15 eV and a change in slope at about 40 eV are observed with the only difference between the current results and those of C(6)H(6) observed in the region 1-100 eV.

In the photoelectron spectrum of N-2 the apparent ionization energy to form the B (2)Sigma(+)(u) state increases linearly with the photon energy. Rotationally resolved measurements of the fluorescent decay of this state show a linear increase of rotational heating with increasing photon energy. These results are in quantitative agreement with the prediction of the theory of recoil-induced rotational excitation, indicating that the rotational heating that has been observed previously arises primarily from such recoil-induced excitation. Together with other results that have been reported they show that recoil-induced internal excitation is significant in many situations, including near threshold.

We have studied the properties of guiding of Ne7+ ions through nanocapillaries in insulating PET polymers for incident energies from 3.5 to 7 keV with a two-dimensional position sensitive detector. During the intensity evolution of transmitted ions, the deflection angle of the transmitted Ne7+ ions shows a few oscillations before approaching an equilibrium value. The experimental results are interpreted in terms of a scenario where the deflection angles of transmitted ions are governed by charge patches formed on the inner wall of the capillary. In addition, the memory effect of charge patches retained from previous irradiation are studied.

Dynamic features of the guiding of Ne7+ ions through nanocapillaries in insulating PET polymers were investigated for incident energies from 3.5 to 7 keV. The deflection angle of the transmitted Ne7+ ions shows a few oscillations before approaching an equilibrium value. The experimental results are interpreted in terms of a scenario where the deflection angles of transmitted ions are governed by charge patches formed on the inner wall of the capillary. In addition, the memory effects of different charge patches retained from previous irradiations are studied.

In this paper, we present new normalized experimental differential cross sections for electron impact excitation of the n = 2 states in helium. The incident electrons have energies in the range 23.5-35 eV, while the scattered electrons are detected over the angular range 10-130°. Corresponding theoretical results from our convergent close-coupling approach are also presented and in general are in very good accord with our measured data. Where possible, a comparison of the present experimental and theoretical results with those from previous measurements is also made. The case for the n = 2 levels in helium constituting a benchmark cross section data set is examined. © 2009 IOP Publishing Ltd.

Slow positron beam was injected into a non-tapered glass capillary which was tilted angle of theta from the beam axis by a movable stage. Beam profiles of the positrons transported through the capillary were observed with a phosphor screen combined with micro channel plates

We have studied the properties of guiding of Ne7+ ions through nanocapillaries in insulating PET polymers for incident energies from 3.5 to 7 keV with a two-dimensional position sensitive detector. During the intensity evolution of transmitted ions, the deflection angle of the transmitted Ne 7+ ions shows a few oscillations before approaching an equilibrium value. The experimental results are interpreted in terms of a scenario where the deflection angles of transmitted ions are governed by charge patches formed on the inner wall of the capillary. In addition, the memory effect of charge patches retained from previous irradiation are studied. © 2009 IOP Publishing Ltd.

We report inelastic and superelastic excitation function measurements for electron scattering from the ground vibrational quantum (000), the bending vibrational quantum (010) and the unresolved first bending overtone (020) and symmetric stretch (100) modes of the ground-electronic state in hot (700 K) carbon dioxide (CO2) molecules. The incident electron energy range of these measurements was 1-9 eV, with the relevant excitation functions being measured at the respective electron scattering angles of 30 degrees, 60 degrees, 90 degrees and 120 degrees. Where possible comparison is made to the often quite limited earlier data, with satisfactory agreement typically being found to within the cited experimental errors. (c) 2008 Elsevier B. V. All rights reserved.

Doubly excited core-hole states of carbon monoxide in the photon energy region of 300-305 eV, i.e., directly above the C 1s ionization threshold, have been studied using both angle-resolved ion-yield and high-resolution resonant Auger spectroscopies. The leading configurations of the most prominent doubly excited Rydberg states are assigned by careful analysis of the ion-yield spectra and the final-state spectra to C 1s(-1) (5 sigma(-1)2 pi(1)S=1) 3s sigma (v'=0,1,2), C 1s(-1) (5 sigma(-1)2 pi(1)S=0) 3s sigma (v'=0,1,2), and C 1s(-1) (5 sigma(-1)2 pi(1)S=1) 4s sigma (v'=0,1), which can only be populated via a conjugate shake-up process. Analysis of the resonant Auger spectra provides an assignment of several two-hole-one-electron (2h-1e) final states.

We report soft X-ray total ion yield and angular-resolved ion yield spectra of CF(3)I in the C 1s, I 3d and F 1s ionisation regions, and tentatively assign the observed electronic states. Anisotropy in ion yield is observed only for the C 1s --> sigma(c-1) transition, indicating that the dipole moment for this transition is parallel to the C(3v). The effusive source of CF(3)I is heated to 800 K to produce a mixture of CF(3) and I, and the resulting spectra are compared to those recorded at room temperature. (C) 2008 Elsevier B.V. All rights reserved.

We have applied both high-resolution photoelectron and Auger spectroscopy to study the N 1s core ionization of N(2). From the respective spectra we are able to show that the Auger decay involves delocalized description of core-hole states. Specifically, the Auger spectra of the N 1s sigma(g,u) core holes to the quasi-stable final states X (1)Sigma(+)(g) and D (1)Sigma(+)(u) are presented. They exhibit the gerade/ungerade splitting as well as vibrational progressions. The 1s sigma(g)/1s sigma(u) Auger intensity ratios are, in agreement with ab initio calculations, congruent to 2.1 and congruent to 0.8 for the X and the D states respectively. The large value for the X state can qualitatively be related to the gerade or ungerade symmetry of the Auger electron.

Differential and integral cross sections for electron-impact excitation of the dipole-allowed B (1)Sigma(+)(u) and C (1)Pi(u) electronic states of molecular hydrogen have been measured. The differential cross sections were determined by analysis of normalized energy-loss spectra obtained using a crossed-beam apparatus at the electron-impact energies of 40, 100, and 200 eV. Integral cross sections were subsequently derived from these data. The present work was undertaken in order to investigate some ambiguities between earlier experimental data and recent BEf-scaled cross sections as defined and calculated by Kim [J. Chem. Phys. 126, 064305 (2007)] and also to extend the energy range of the available data. Optical oscillator strengths, also determined as a part of the present investigation, were found to be in fair accordance with previous measurements and some calculations.

We consider the efficacy of the BEf-scaling approach, in calculating reliable integral cross sections for electron impact excitation of dipole-allowed electronic states in molecules. We will demonstrate, using specific examples in H2, CO and H2O, that this relatively simple procedure can generate quite accurate integral cross sections which compare well with available experimental data. Finally, we will briefly consider the ramifications of this to atmospheric and other types of modelling studies. © 2008 IOP Publishing Ltd.

We report absolute differential and integral cross-sections for excitation of the six lowest lying electronic states in water. The incident electron energy for this study was 15 eV and the scattered electron angular range, for the differential cross-section measurements, was 10-90 degrees. Where possible comparison of the present cross-sections with the corresponding results from theory is made, the level of agreement between them being found to be somewhat marginal. (c) 2007 Elsevier B.V. All rights reserved.

The vibrationally resolved partial cross sections sigma(nu') and asymmetry parameters beta(nu') for the photoionization of the NO molecule producing NO(+) N (1s(-1))(3)Pi, (1)Pi ions in the vibrationally excited states nu' are measured for photon energies between 412 and 419 eV, across the sigma* shape resonance region above the N K-shell ionization threshold. The position of the maximum of sigma(3 Pi, 1 Pi)(nu') for the N (1s(-1)) is observed to move towards the N (1s(-1))(3)Pi and (1)Pi thresholds in both channels with increasing vibrational excitation in the parent ion. The beta(3 Pi, 1 Pi)(nu') curves, on the other hand, exhibit monotonic increase in the investigated photon energy range. The major features are fairly well reproduced by ab initio vibrationally specific calculations based on the multichannel Schwinger configuration interaction (MCSCI) method for the dipole transition moments, where the effects of vibrational motion on the photoionization cross sections are included using the adiabatic approximation.

In this paper we investigate electron and positron total and electron vibrational excitation scattering cross sections for propene and cyclopropane molecules. The electron and positron total cross sections were measured over the energy range 0.2-1000 eV using a retarding-potential time-of-flight method while the electron impact vibrational excitation cross sections were measured using a crossed-beam method. For both molecules, bending and stretching vibrational modes are studied at loss energies 0.12 and 0.37 eV, respectively, for propene, and 0.13 and 0.37 eV, respectively, for cyclopropane, at the scattering angle of 90 degrees and impact energy range 1-16 eV.

The carbon Is photoelectron spectrum of CF(4) measured at photon energies from 330 to 1500 eV shows significant contributions from nonsymmetric vibrational modes. These increase linearly as the photon energy increases. The excitation of these modes, which is not predicted in the usual Franck-Condon point of view, arises from the recoil momentum imparted to the carbon atom in the ionization process. A theory is presented for quantitative prediction of the recoil effect; the predictions of this theory are in agreement to the measurements. The experiments also yield the vibrational frequencies of the symmetric and asymmetric stretching modes in core ionized CF4, the change in CF bond length upon ionization, -0.61 pm, and the Lorentzian linewidth of the carbon Is hole, 67 meV. (C) 2008 American Institute of Physics.

We apply the method of Kim (2007 J. Chem. Phys. 126 064305) in order to derive integral cross sections for the (1)Sigma(+)(u) and (1)Pi(u) states of CO(2), from our corresponding earlier differential cross section measurements (Green et al 2002 J. Phys. B: At. Mol. Opt. Phys. 35 567). The energy range of this work is 20-200 eV. In addition, the BEf-scaling approach is used to calculate integral cross sections for these same states, from their respective thresholds to 5000 eV. In general, good agreement is found between the experimental integral cross sections and those calculated within the BEf-scaling paradigm, over the entire common energy range. Finally, we employ our calculated integral cross sections to determine the electron energy transfer rates for these states, for a thermal electron energy distribution. Such transfer rates are in principle important for understanding the phenomena in atmospheres where CO(2) is a dominant constituent, such as on Mars and Venus.

The high-resolution Auger spectrum of CO(2) subsequent to C 1s(-1) photoionization is reported along with the corresponding photoelectron spectrum. Auger transitions to seven quasi-stable final states are observed. They are assigned on the basis of theoretical results in combination with the assumption that the Auger spectrum is dominated by transitions to singlet states. From the vibrational progressions in the Auger spectrum, the vibrational energies h omega, the anharmonicities xh omega and the equilibrium distances R(e) for the dicationic final states are derived in a fit analysis assuming Morse potentials.

A new apparatus for the study of positron scattering on gaseous target is presented. The apparatus uses electrostatic lens elements and a remoderator in a reflection geometry for the brightness enhancement. The system will provide a high quality positron beam with a small diameter and a small angular divergence, even at low energies. (c) 2007 Elsevier B.V. All rights reserved.

Symmetry-resolved ion-yield spectroscopy of vibrationally excited N(2)O in the vicinity of the O 1s ionization threshold has been carried out using an angle-resolved ion detection technique. The spectral intensity of the O 1s -> ns sigma Rydberg series, which has sigma* valence character, is significantly reduced by the excitation of the bending vibration in the electronic ground state. Using an ab initio analysis of the electronic part of the second moment < r(2)>, this suppression is interpreted as being due to a decrease in the mixing of the valence character in the ns sigma Rydberg states with decreasing bond angle.

A photochemistry study on nitrous oxide making use of site-selective excitation of terminal nitrogen, central nitrogen, and oxygen 1s -> 3 pi excitations is presented. The resonant Auger decay which takes place following excitation can lead to dissociation of the N2O+ ion. To elucidate the nuclear dynamics, energy-resolved Auger electrons were detected in coincidence with the ionic dissociation products, and a strong dependence of the fragmentation pathways on the core-hole site was observed in the binding energy region of the first satellite states. A description based on the molecular orbitals as well as the correlation between the thermodynamical thresholds of ion formation and the first electronic states of N2O+ has been used to qualitatively explain the observed fragmentation patterns. (c) 2008 American Institute of Physics.

We report differential cross-section measurements for electron-impact excitation of the C (1)Sigma(+)+c (3)Pi and E (1)Pi electronic states in carbon monoxide. The energy range of this work is 30-200 eV. Where a comparison is possible, reasonable agreement is found with the earlier 20-50 eV results from Middleton [J. Phys. B 26, 1743 (1993)]. A generalized oscillator strength analysis of the present differential cross-section data enables us to determine estimates of the corresponding integral cross sections, which are compared to results from the BEf-scaling approach [Y.-K. Kim, J. Chem. Phys. 126, 064305 (2007)] calculated as a part of this study. Very good agreement between them is in general found. Finally our 100-eV and 200-eV generalized oscillator strength data are also employed to determine values of the respective C (1)Sigma(+) and E (1)Pi optical oscillator strengths, with excellent agreement being found between them and the previous dipole (e,e) results from Chan [Chem. Phys. 170, 123 (1993)].

We present an experimental observation of the electronic Doppler effect in resonant Auger spectra upon core excitation slightly above the carbon K edge of the CO molecule. Thus the electronic Doppler effect has been identified in above-threshold excitation, and in a transition of Pi symmetry. Ab initio calculations of the potential energy curves of the relevant states of CO and the wave packet technique have been employed to provide a theoretical background to the experimental studies. The weak feature around 299.4 eV in the photoabsorption spectrum, whose decay has been investigated by the present experiment, is assigned to double (core-valence) excitations to C 1s shake-up states vertical bar 1s(C)(-1)1 pi(-1)pi(*2)> with a strong dissociative character, and the Doppler splitting of the atomic peak has been reproduced by the simulation.

The boron 1s photoelectron spectrum of (11)BF(3) has been measured at a photon energy of 400 eV and a resolution of about 55 meV. The pronounced vibrational structure seen in the spectrum has been analyzed to give the harmonic and anharmonic vibrational frequencies of the symmetric stretching mode, 128.1 and 0.15 meV, as well as the change in equilibrium BF bond length upon ionization, -5.83 pm. A similar change in bond length has been observed for PF(3) and SiF(4), but a much smaller change for CF(4). Theoretical calculations for BF(3) that include the effects of electron correlation give results that are in reasonable accord with the experimental values. The Lorentzian (lifetime) width of the boron 1s core hole in BF(3) is found to be 72 meV, comparable to the value of 77 meV that has been reported for CF(4). (C) 2007 American Institute of Physics.

We present experimental evidence for pronounced electron transfer from C to F(+) happening during the breakup of CH(3)F(+) ions in gas phase produced by resonant photoemission following F 1s -> 6a(1)(*) core excitation of CH(3)F. We measured the momentum of the ionic fragments in coincidence with the F KVV Auger electrons that show a Doppler shift reflecting the motion of the F nucleus. The correlation between Doppler shift and ion momentum is opposite for the F(+) and the CH(2)(+) fragments, indicating that CH(2)(+) is produced by electron transfer from C to F(+), after the Auger electron emission from excited moving F. This finding is rationalized by calculations of the potential energy curves of the main states involved in the excitation and decay processes.

Observations of Auger transitions to quasi-stable states of CO2+ subsequent to C 1s(-1) and O 1s(-1) ionizations of CO are presented along with the corresponding photoelectron spectra and calculations of the potential energy curves. The equilibrium distances Re, the vibrational energies h omega, and the anharmoncities xh omega for the final states a(1)Sigma(+), b(1)Pi, A(3)Sigma(+) and d(1)Sigma(+) are derived from fits to the spectra by assuming Morse potentials. A comparison of these Morse potentials with theoretical potential energy curves reveals excellent agreement in the Franck-Condon regions of the Auger transitions. The relative intensities for the observed C 1s(-1) and O 1s(-1) Auger transitions are also derived. (C) 2007 Elsevier B.V. All rights reserved.

Decay spectra of N2O following excitation to the N terminal (Nt). pi*, N central (N-c). pi* and O 1s -> pi* intermediate states are reported. The final states reached after participator decay show resonant enhancement consistent with a local-density-of-states analysis based on the Mulliken population of the valence molecular orbitals. In particular, the X-state is resonantly enhanced mostly after excitation from the N-t 1s and the O 1s core levels to the pi*, while the B-state is mostly enhanced following the excitation of the N-c 1s -> pi* intermediate state. Below the N-t 1s threshold, the lowest lying peak related to spectator decay falls at lower binding energy than the highest lying participator peak. This can be attributed to a particularly strong screening effect exerted by the excited electron in the LUMO.

Methane and deuteromethane molecules were core ionized using synchrotron radiation, and the ionic fragments from the molecular dissociation were detected in coincidence with the Auger electrons. The electron - ion coincidence spectra are analysed in terms of partial ion yields and ion kinetic energy distributions, both as functions of electron kinetic energy. The dependence of the fragmentation patterns on the electronic character of the Auger final states as well as on the excess energy available for dissociating the molecule is studied. The analysis reveals marked differences in the dissociation of the 2a(1)(-2) and 2a(1)(-1) 1t(2)(-1) states, interpreted as an `excess- energy- dependent' concerted dissociation process for the 2a(1)(-2) state and an ` electronic- state- dependent' sequential process for the 2a(1)(-1) 1t(2)(-1) state.

The transmission of highly charged ions through nanocapillaries in insulating polyethylene terephthalate (PET) polymers was investigated. In experiments at laboratories in RIKEN (Japan) and HMI (Germany) different detection methods were applied to study the ion current dependence in a wide range covering two orders of magnitude. At HMI an electrostatic ion spectrometer was used and at RIKEN a two-dimensional position sensitive detector was implemented. New PET samples with parallel capillaries and low density were manufactured. For tilted capillaries, the ions are guided along the capillary axis, since the majority of ions are deflected in a charge patch created in the capillary entrance. The results provide insights into the mechanisms of capillary guiding. The fraction of transmitted ions was found to be nearly independent on the incident ion current indicating a sudden increase in the discharge current depleting the entrance charge patch. The experimental results were well-reproduced by model calculations based on a nonlinear (exponential) expression for the discharge current.

We report differential cross sections and optical oscillator strength determinations for the respective excitation of vibrational sub-levels of the A(2)Sigma(+), C-2 Pi and D-2 Sigma(+) electronic states in NO by 100 eV electrons. While the differential cross section measurements are original, the present optical oscillator strengths are compared where possible with earlier values. In particular, a detailed comparison is made with the dipole (e,e) spectroscopy data from Chan et al. [W.F. Chan, G. Cooper, C.E. Brion, Chem. Phys. 170 (1993) 111], with generally very good agreement being found. (c) 2007 Elsevier B.V. All rights reserved.

We have measured the vibrationally resolved partial cross sections sigma(')((v1),v(2)('),v(3)(')) and asymmetry parameters beta(')((v1),v(2)('),v(3)(')) for N-c and N-t K-shell photoionization of the N2O molecule in the sigma* shape resonance region above the N-t and N-c K-shell ionization thresholds. N-c K-shell photoionization of the N2O molecule predominantly causes the excitation of the quasisymmetric vibrations (v(1)(')), whereas N-t K-shell photoionization causes both quasisymmetric and quasiantisymmetric vibrations (v(1)(') and v(3)(')) to be excited. The shape resonance energy in the N-c K-shell photoionization increases with an increase in v(1)('). The beta(')((v1),0,0) curves for the N-c K-shell photoionization exhibit maxima at energies close to the shape resonance energies for the individual values of v(1)('). The shape resonance energy in the N-t K-shell photoionization decreases with an increase in v(1)(') and slightly increases with an increase in v(3)('). The beta(')((v1),0,0) curves show a significant state dependence in the region of the shape resonance, with the curves shifting to lower energy as v(1)(') increases. The vibrational state dependence of the cross sections sigma(')((v1),v(2)('),v(3)(')) and asymmetry parameters beta(')((v1),v(2)('),v(3)(')) are well reproduced by the theoretical calculations using the multichannel Schwinger configuration interaction (MCSCI) method, including both the N-c and N-t ion states.

Electron and positron cross sections for scattering from toluene molecules have been investigated both experimentally and theoretically over the energy range 0.4-1000 eV. Peaks have been observed in the electron total cross sections (TCSs) at 1.4, 4.5, and 8.0 and a shoulder at about 40 eV. Vibrational and elastic differential cross section experiments were carried out to probe the origin and nature of these peaks. The continuum multiple scattering method was used to calculate elastic integral cross sections for electron impact. Although the 1.4 eV peak is dominated by the elastic channel, strong contributions from the CH3 asymmetric bending and stretching vibrational modes are also observed. The 4.5 eV feature is also observed to be strongly due to vibrational excitation. The broad 7-13 eV peak includes contributions from the CH3 asymmetric bending (peaked at 7 eV) and the CH3 stretching (peaked at 9.5 eV) vibrational modes. Positron TCSs are studied and compared to positron-benzene TCSs. The effect of the CH3 substitution is observed to make a significant contribution to both electron and positron TCSs below 20 eV.

We have measured two-dimensional images of 3.5-7 keV Ne7+ ions guided by PET nanocapillaries as a function of the deposited charge. The transmitted ion position and shape are found to change with the intensity evolution. After saturation of the guided ion intensity, the transmission profile is nearly isotropic and its angular width amounts to about 1 degrees, which differs from previous measurements. (c) 2006 Elsevier B.V. All rights reserved.

We report a detailed analysis of the electronic structure of methyl oxirane, including core-level photoelectron spectroscopy, X-ray absorption at both C and O K-shells, resonant Auger and normal Auger spectroscopy. The X-ray absorption spectra (XAS) around the C K-edge can be easily interpreted on the ground of the chemical shift between the carbon atoms with different chemical environments. The X-ray absorption data around the O K-edge are quite structureless, hinting for a likely fragmentation process (possibly implying a ring-opening reaction). In resonant Auger spectra obtained after excitation below both the C 1s and O 1s ionization thresholds we notice a predominance of spectator decay implying a strong mixing between empty molecular orbitals and Rydberg states. (c) 2007 Elsevier B.V. All rights reserved.

Core-level photoemission from N-2 can be considered an analogue of Young's double-slit experiment (YDSE) in which the double-slit is replaced by a pair of N 1s orbitals. The measured ratio between the 1 sigma(g) and 1 sigma(u) photoionization cross-sections oscillates as a function of photoelectron momentum, due to two-center YDSE interference, exhibiting a remarkable dependence on the vibrational sub-levels of the core ionized state. We theoretically demonstrate that the recoil of the photoelectron given to the ionized N atom strongly influences this interference pattern. The reason for this is that the momentum transfer affects the phases of the photoionization amplitudes. (c) 2007 Published by Elsevier B.V.

1,1-difluoroethylene (1,1-C2H2F2) molecules have been studied for the first time experimentally and theoretically by electron and positron impact. 0.4-1000 eV electron and 0.2-1000 eV positron impact total cross sections (TCSs) were measured using a retarding potential time-of-flight apparatus. In order to probe the resonances observed in the electron TCSs, a crossed-beam method was used to investigate vibrational excitation cross sections over the energy range of 1.3-49 eV and scattering angles 90 degrees and 120 degrees for the two loss energies 0.115 and 0.381 eV corresponding to the dominant C-H (nu(2) and nu(9)) stretching and the combined C-F (nu(3)) stretching and CH2 (nu(11)) rocking vibrations, respectively. Electron impact elastic integral cross sections are also reported for calculations carried out using the Schwinger multichannel method with pseudopotentials for the energy range from 0.5 to 50 eV in the static-exchange approximation and from 0.5 to 20 eV in the static-exchange plus polarization approximation. Resonance peaks observed centered at about 2.3, 6.5, and 16 eV in the TCSs have been shown to be mainly due to the vibrational and elastic channels, and assigned to the B-2, B-1, and A(1) symmetries, respectively. The pi* resonance peak at 1.8 eV in C2H4 is observed shifted to 2.3 eV in 1,1-C2H2F2 and to 2.5 eV in C2F4; a phenomenon attributed to the decreasing C=C bond length from C2H4 to C2F4. For positron impact a conspicuous peak is observed below the positronium formation threshold at about 1 eV, and other less pronounced ones centered at about 5 and 20 eV. (c) 2007 American Institute of Physics.

Vibrationally resolved N-c and N-t K-shell photoelectron spectra of the dinitrogen oxide have been studied experimentally and theoretically. Vibrational frequencies for the N-c and N-t ls ionized states obtained from the 2D potential surfaces computed by the CCSD(T) method within the equivalent core approximation reasonably agree with the experimental values. Experimental relative intensities of the vibrational structure are reasonably reproduced by the multi-channel Schwinger configuration interaction method (MCSCI) with the computed 2D potential surfaces. Improved relaxed geometries of these core-hole states are obtained from fitting the experimental spectra using the MCSCI calculations and regarding the bond lengths as fitting parameters. (c) 2007 Elsevier B.V. All rights reserved.

Vibrationally resolved C 1s and O 1s photoelectron spectra of carbon dioxide have been measured with photon energies up to 500 and 700 eV, respectively. Vibrational branching ratios are nearly constant for the C 1s and O 1s photoelectron spectra recorded with the photon energies in the regions 400-500 and 600-700 eV, respectively, where neither shape resonance effect nor photoelectron recoil effect is significant. The information about the potential curves for the C 1s and O 1s ionized states are extracted from these spectra, using the Franck-Condon approximation. The experimental potential curves thus obtained are well reproduced by the present ab initio calculations based on the symmetry adapted cluster-configuration interaction (SAC-CI) method. (c) 2006 Elsevier B.V. All rights reserved.