小田切 丈

The differential cross sections of the dissociative double excitations resulting in H(2p)<br /> formation in 80 eV electron collisions with H2 have been measured at electron scattering<br /> angles of 3, 20, 30 and 40◦ by means of angle-resolved electron energy loss spectroscopy in<br /> coincidence with detecting Lyman-α photons. The doubly excited states of H2 involved in this<br /> study are the optically allowed Q1<br /> 1u(1) and Q2<br /> 1u(1) states and the forbidden state at 26 eV,<br /> which has not been assigned so far and is temporarily referred to as the F state in this study. At<br /> a 3◦ electron scattering angle the differential cross section of the dissociative excitation to the<br /> forbidden F state is the largest among those for the three doubly excited states and decreases<br /> with increasing the electron scattering angle more rapidly than those for the allowed Q1<br /> 1u(1)<br /> and Q2<br /> 1u(1) states. The differential cross sections for the forbidden and allowed states do not<br /> differ quite so much, which may show that the forbidden F state is a dissociative state rather<br /> than an autoionizing state. The effective generalized oscillator strengths for H(2p) formation<br /> have been compared with

An experimental technique for the measurement of the total cross section for electron scattering from atoms and molecules at high resolution is described. The total cross sections for electron scattering from Kr in the energy range from 14 meV to 20 eV obtained with the technique are also reported. The present technique employs a combination of the penetrating field technique and the threshold photoionization of rare-gas atoms using synchrotron radiation as an electron source in order to produce a high-resolution electron beam at very low energy. The characteristics of the electron sources were determined by measuring the ionizing photon energy dependence of photoelectron yield. Absolute total cross sections for electron scattering are obtained by the attenuation method. The measured absolute values of the total cross sections for electron scattering from Kr agree with those obtained by other groups down to 175 meV, above which several experimental works have been reported. Below 175 meV, the present results generally agree with theoretical cross sections down to 14 meV. The resonant structures in the total cross sections due to Kr- (4p55s22P3/2) and the Kr- (4p55s22P1/2) Feshbach resonances are also reported. The resolution of the present setup has been estimated from a fit of the measured profile of the Kr- (4p55s22P3/2) resonance by the theoretical curve obtained from the resonant scattering theory. © 2010 The American Physical Society.

An experimental technique for the measurement of the total cross section for electron scattering from atoms and molecules at high resolution is described. The total cross sections for electron scattering from Kr in the energy range from 14 meV to 20 eV obtained with the technique are also reported. The present technique employs a combination of the penetrating field technique and the threshold photoionization of rare-gas atoms using synchrotron radiation as an electron source in order to produce a high-resolution electron beam at very low energy. The characteristics of the electron sources were determined by measuring the ionizing photon energy dependence of photoelectron yield. Absolute total cross sections for electron scattering are obtained by the attenuation method. The measured absolute values of the total cross sections for electron scattering from Kr agree with those obtained by other groups down to 175 meV, above which several experimental works have been reported. Below 175 meV, the present results generally agree with theoretical cross sections down to 14 meV. The resonant structures in the total cross sections due to Kr- (4p(5)5s(22)P(3/2)) and the Kr- (4p(5)5s(22)P(1/2)) Feshbach resonances are also reported. The resolution of the present setup has been estimated from a fit of the measured profile of the Kr- (4p5(5)s(22)P(3/2)) resonance by the theoretical curve obtained from the resonant scattering theory.

The cross sections for the emission of Lyman-α fluorescence in the photoexcitation of H2O have been measured as a function of the incident photon energy in the 14-60 eV range, i.e. the outer-and inner-valence ranges. Four superexcited states have been found, two of which are doubly excited states, one is a singly excited state and one a state including electron configurations of both single and double excitations. The gross feature of the superexcited states of H2O resulting in the formation of excited hydrogen atoms has been obtained by combining the present results and the cross section curves of the Balmer fluorescences (Kato et al 2004 J. Phys. B: At. Mol. Opt. Phys. 37 3127). The breakdown of the independent electron model has been indicated in the inner-valence range of H2O, and the degree of breakdown has been compared among CH4, NH3 and H 2O ten-electron molecules. © 2010 IOP Publishing Ltd.

The cross sections for the emission of Lyman-alpha fluorescence in the photoexcitation of H(2)O have been measured as a function of the incident photon energy in the 14-60 eV range, i.e. the outer-and inner-valence ranges. Four superexcited states have been found, two of which are doubly excited states, one is a singly excited state and one a state including electron configurations of both single and double excitations. The gross feature of the superexcited states of H(2)O resulting in the formation of excited hydrogen atoms has been obtained by combining the present results and the cross section curves of the Balmer fluorescences (Kato et al 2004 J. Phys. B: At. Mol. Opt. Phys. 37 3127). The breakdown of the independent electron model has been indicated in the inner-valence range of H(2)O, and the degree of breakdown has been compared among CH(4), NH(3) and H(2)O ten-electron molecules.

We have measured the coincidence time spectra of two Lyman-α photons emitted by a pair of H(2p) atoms in the photodissociation of H2 at the incident photon energy of 33.66 eV and at the hydrogen gas pressures of 0.40 and 0.02 Pa. The decay time constant at 0.02 Pa is approximately half the lifetime of a single H(2p) atom, 1.60 ns, while the decay time constant at 0.40 Pa is in agreement with the lifetime of a single H(2p) atom. It turns out that the decay faster than the lifetime of a single H(2p) atom originates from the entanglement in the pair of H(2p) atoms. We have demonstrated an effect of entanglement on atomic decay. © 2010 The American Physical Society.

The differential cross sections for the dissociative single and double excitations resulting in H(2p) formation with the excitation energy of 19-46 eV in electron-CH4 collisions have been measured as a function of electron scattering angle in the range 4°-48° at 80 eV incident electron energy by means of angle-resolved electron energy-loss spectroscopy in coincidence with detecting Lyman-α photons. This is the first measurement of the differential cross sections for the dissociative double excitations as a function of electron scattering angle in electron-molecule collisions. Their fractions have been compared with those at the optical limit calculated from the density of the dipole oscillator strength for the emission of Lyman-α photons previously measured by our group. The dissociative double excitations in 80 eV electron collisions seem to be brought about in a very different way from those at the optical limit where they arise from the electron correlation in a methane molecule. The differential cross sections have also been discussed in terms of momentum transfer, leading to a universal curve. © 2010 IOP Publishing Ltd.

A novel method of spectroscopy for highly excited states of molecules in the valence excitation<br /> range has been established through the detection of metastable hydrogen atoms in the 2s state<br /> formed by photoexcitation. The detector for the metastable hydrogen atom is composed of a stack<br /> of parallel plate electrodes that creates a localized electric field and triggers the emission of the<br /> Lyman- photon from the atom and a chevron pair of microchannel plates that detects the photon.<br /> For linear molecules, the angle-resolved detection of the metastable hydrogen atom enables us to<br /> measure cross sections in which electronic symmetries of highly excited molecular states are<br /> resolved. Such symmetry-resolved cross section measurements were carried out for doubly excited<br /> states of H2.

Doubly excited states of CH(4) in electron collisions were investigated for the first time by measuring electron energy-loss spectra tagged with the emission of the Lyman-alpha photon. It turned out that the collisional cross section resulting in the emission of the Lyman-alpha photon originating from the doubly excited states are larger than or comparable to those originating from the nearby singly excited states and the electron interaction with molecules promotes the double excitation against the single excitation as compared with the photon interaction.

Doubly excited states of CH4 in electron collisions were investigated for the first time by measuring electron energy-loss spectra tagged with the emission of the Lyman-α photon. It turned out that the collisional cross section resulting in the emission of the Lyman-α photon originating from the doubly excited states are larger than or comparable to those originating from the nearby singly excited states and the electron interaction with molecules promotes the double excitation against the single excitation as compared with the photon interaction. © 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.

The differential cross sections for electron scattering accompanied by the emission of a Lyman-α photon in electron-CH4 collisions have been measured as a function of electron energy-loss and scattering angle in the range of energy loss of doubly excited states at 80eV incident electron energy.

The cross sections for the generation of a fluorescence photon pair following photoexcitation of NO, differential with respect to the solid angles of the emission directions of the two photons, have been measured as a function of incident photon energy to investigate superexcited states of NO in the inner-valence range, in particular around the double ionization potential. Superexcited states of NO in the range 25-47 eV have been newly found as resonance peaks in the cross-section curve. We determined that the superexcited states are singly inner-valence excited and multiply excited states of NO. It is remarkable that there exist superexcited states of NO dissociating into neutral fragments even in the range above the double ionization potential at 38.476 eV. A dip in the cross-section curve is observed around 40 eV; the origin is discussed in terms of the decay dynamics of the superexcited states embedded in the double electronic continuum.

水素分子２電子励起状態の解離により生成する原子対からのLyman-alpha光子対の放出角度相関を測定し、角度相関理論と比較することにより、水素原子対が量子もつれ状態にあることを示した。また量子もつれ状態が圧力により変化することから、量子もつれ原子対の環境との反応断面積を定義し、おおよその値を見積もった。

The angular distribution of two Lyman-alpha photons, i.e., the probability density that two Lyman-alpha photons are emitted in given directions, in the photodissociation of a hydrogen molecule have been measured at the hydrogen gas pressures of 0.40 and 0.13 Pa. We have found that the experimental angular distributions seem to approach the theoretical one by our group [J. Phys. B 40, 617 ( 2007)] with decreasing pressure, which indicates the generation of the entangled pair of H(2p) atoms shown in the theory and the role of the reaction of the entangled pair of H(2p) atoms with an H-2 molecule that efficiently changes the entanglement.

The cross sections for the generation of a pair of fluorescence photons in the photoexcitation of O(2) differential with respect to solid angles for the emission of the photon pair have been measured as a function of incident photon energy in the range 23-47 eV using the photon-photon coincidence method, the (gamma, 2 gamma) method, to investigate the inner-valence excited states and multiply excited states of O(2) as superexcited states. Four superexcited states of O(2) with the (3)Sigma(-)(u) or (3)Pi(u) symmetry have been newly found around 29, 36, 38 and 44 eV in the measured cross section curve free from ionization. It turns out that they are inner-valence excited states and multiply excited states. Two remarkable points are shown: (1) there exist superexcited states of O(2) dissociating into neutral fragments even in the energy range above the double-ionization potential of O(2) at 36.13 eV and (2) the values of the doubly differential cross sections decrease to a large extent around the double-ionization potential with increasing incident photon energy, both of which have been compared with the results of N(2) by our previous (gamma, 2 gamma) experiment. The origin of (2) is discussed in detail.

The cross sections for the generation of a pair of fluorescence photons in the photoexcitation of O2 differential with respect to solid angles for the emission of the photon pair have been measured as a function of incident photon energy in the range 23-47 eV using the photon-photon coincidence method, the (γ, 2γ) method, to investigate the inner-valence excited states and multiply excited states of O2 as superexcited states. Four superexcited states of O2 with the 3Σ -u or 3Πu symmetry have been newly found around 29, 36, 38 and 44 eV in the measured cross section curve free from ionization. It turns out that they are inner-valence excited states and multiply excited states. Two remarkable points are shown: (1) there exist superexcited states of O2 dissociating into neutral fragments even in the energy range above the double-ionization potential of O2 at 36.13 eV and (2) the values of the doubly differential cross sections decrease to a large extent around the double-ionization potential with increasing incident photon energy, both of which have been compared with the results of N2 by our previous (γ, 2γ) experiment. The origin of (2) is discussed in detail. © 2009 IOP Publishing Ltd.

The cross sections for the generation of a fluorescence photon pair following photoexcitation of NO, differential with respect to the solid angles of the emission directions of the two photons, have been measured as a function of incident photon energy to investigate superexcited states of NO in the inner-valence range, in particular around the double ionization potential. Superexcited states of NO in the range 25-47 eV have been newly found as resonance peaks in the cross-section curve. We determined that the superexcited states are singly inner-valence excited and multiply excited states of NO. It is remarkable that there exist superexcited states of NO dissociating into neutral fragments even in the range above the double ionization potential at 38.476 eV. A dip in the cross-section curve is observed around 40 eV the origin is discussed in terms of the decay dynamics of the superexcited states embedded in the double electronic continuum. © 2009 IOP Publishing Ltd.

The formation and decay of doubly excited ammonia produced by photon and electron interactions have been investigated through measuring (i) the cross sections for the emission of the Lyman-α fluorescence in the photoexcitation of NH3 as a function of incident photon energy in the range 15-60 eV and (ii) the electron-energy-loss spectrum of NH3 tagged with the Lyman-α photons at 100 eV incident electron energy and 8° electron scattering angle in the range of the energy loss 15-48 eV. Six superexcited states have been found, four of which are doubly excited states with one being a singly excited state and the other being a state including electron configurations of a single excitation and double excitations. There exist two forbidden doubly excited states whose widths are approximately 1 eV, i.e. much sharper than the allowed superexcited states in the electron-energy-loss spectrum tagged with the Lyman-α photons. It is remarkable that the electron interaction with NH3 at 100 eV incident electron energy and 8° electron scattering angle promotes the ratio of the oscillator strength for the double excitation to that for the single excitation as compared with the photon interaction. © 2008 IOP Publishing Ltd.

電子衝突による分子の2電子励起過程を研究する手段として有効な、光子放出過程と同期した電子エネルギー損失スペクトル測定のための装置検出感度を大幅に向上させ、電子散乱角度依存性についての議論を可能にした。

窒素分子の放射光励起に伴い放出される2光子を同時計数することにより、2光子放出断面積を測定した。断面積カーブ中に2重イオン化ポテンシャル付近の窒素分子多電子励起状態を観測した。2重イオン化ポテンシャル以上においても中性励起状態が存在し、それらが中性解離している証拠を得た。

分子の放射光励起に伴い放出される真空紫外域の2光子を同時計数し、これまで観測不可能であった分子高励起状態のスペクトルを測定し、解離ダイナミックスについて議論した。

窒素分子の2光子放出断面積を入射光子エネルギーの関数として測定し、連続状態の寄与を一切含まない中性多電子励起状態のスペクトルを得た。

メタンの電子衝突による2電子励起と放射光励起による2電子励起を振動子強度を通して比較し、1電子励起に対する2電子励起の割合が電子衝突の方が大きく、2電子励起を促進させるメカニズムが電子衝突にあることを明らかにした。

放射光励起に伴う２光子放出過程の断面積カーブを測定することにより、純粋に水素分子２電子励起状態のみのスペクトルを得た。解離ダイナミックスが半古典論で良く説明つくことを明らかにした。

放射光励起に伴う水分子からの蛍光放出断面積絶対値を、可視紫外部の各蛍光ラインごとに、入射光子エネルギーの関数として測定した。過去に測定したCH4、NH3の同様の断面積と比較し、2電子励起状態の生成と崩壊について議論した。

蛍光放出を伴う解離過程と同期した電子エネルギー損失スペクトルを測定し、分子の光学的禁制２電子励起状態の存在を初めて明らかにし、それらが解離的性質を持っていることを明らかにした。

Electron energy-loss spectra of H2, D2 and N 2 tagged with emissive neutral-dissociation, i.e. coincident electron-energy-loss spectra, were measured in the range where doubly excited states of these molecules lie. The doubly excited states, in particular forbidden ones with dissociative character, were revealed for the first time in electron-molecule collisions. It has turned out that this method, the coincident electron-energy-loss spectroscopy, is a key tool for investigating doubly excited molecules. © Physica Scripta 2004.

Electron energy-loss spectra of H-2, D-2 and N-2 tagged with emissive neutral-dissociation, i.e. coincident electron-energy-loss spectra, were measured in the range where doubly excited states of these molecules lie. The doubly excited states, in particular forbidden ones with dissociative character, were revealed for the first time in electron-molecule collisions. It has turned out that this method, the coincident electron-energy-loss spectroscopy, is a key tool for investigating doubly excited molecules.

アンモニアからの可視紫外蛍光放出過程の断面積絶対値を入射光子エネルギーの関数として測定し、独立粒子モデルの予想から大きく外れた大きな2電子励起状態の寄与を見出した。メタンで見られた特異性がアンモニアにも観測されることを示した。

The cross sections for the collisional deexcitation of neon atoms in the lowest excited (1)P(1) state by Ar, Kr, Xe, N(2), O(2), CO, NO, and CH(4), and in the lowest excited (3)P(1) state by O(2) and CH(4) have been measured at a mean collisional energy corresponding to room temperature. Data are also included for collisions of argon atoms in the lowest excited (1)P(1) and (3)P(1) states by C(2)H(4), cyclo-C(3)H(6), and C(3)H(8), and collisions of krypton atoms in the lowest excited (1)P(1) and (3)P(1) states by C(2)H(4) and cyclo-C(3)H(6). The measured cross sections, together with those obtained in our previous studies, are compared with the cross sections calculated using the Watanabe-Katsuura theory. An extension of the Watanabe-Katsuura theory to the deexcitation of excited rare gas atoms in collisions with molecular quenchers, not atoms, is examined. (C) 2003 American Institute of Physics.

The single-hole one-electron superexcited states and doubly-excited states of H(2), D(2), N(2) and O(2) have been investigated by means of the coincident electron-energy-loss spectroscopy that we developed. In this method the electron-energy-loss spectra tagged with the vacuum ultraviolet fluorescences emitted by the neutral fragments produced from superexcited molecules are measured by means of electron-photon coincidence technique. The contribution from ionization in this sort of electron-energy-loss spectra is suppressed to a large extent, and thus the structures attributed to the superexcited states of molecules become highlighted. The comparison with the photoexcitation experiments by means of the oscillator strengths give us clear discrimination between allowed and forbidden superexcited-states. As to H(2), D(2), and N(2), the doubly-excited states including those found in the present experiment have been investigated in terms of both their energies and dynamical behavior. A new possibility of the coincident electron-energy-loss spectroscopy has been established in investigating the single-hole one-electron superexcited states Of O(2): the time-resolved coincident electron-energy-loss spectrum has been measured to distinguish between the direct process producing excited oxygen atoms and indirect one due to cascade transition. It has turned out that the coincident electron-energy-loss spectroscopy is a key tool for investigating superexcited molecules.

The absolute values of the fluorescence cross sections for CH(A, B --&gt; X) and H(n = 4-7 --&gt; n' = 2) in the photoexcitation of methane have been obtained as a function of incident photon energy in the range 12.65-41 eV, in which five superexcited states have been found and discussed quantitatively in detail. The lower two of them are single-hole one-electron superexcited states and the higher three around 25, 29 and 35 eV are doubly excited states, which have been investigated in detail for the first time in this experiment. It is remarkable that the oscillator strengths for the emission of the fluorescences originating from the doubly excited states are as large as or even larger than those from the single-hole one-electron superexcited (2a(1))(-1) (npt(2)) T-1(2) states, which seems not to be amenable to the independent electron model.

メタンの可視紫外蛍光放出断面積絶対値を入射光子エネルギーの関数とし測定し、断面積中の2電子励起状態の寄与が独立粒子モデルの予想から外れ、非常に大きいことを示した。

励起希ガス原子の脱励起断面積を測定し、Watanabe-Katsuura（WK）理論と比較した。WK理論とのずれの大きさを光イオン化の量子収率と比べ、理論に修正の余地ありと結論付けた。

The ordinary and coincident electron-energy-loss spectra of N-2 have been measured in an expected energy range for the formation of doubly excited states to investigate their formation and decay processes in electron-N-2 collisions. The present results are compared with those obtained by photoexcitation experiments. Existence of the optically forbidden doubly excited states and their dissociative character have been revealed clearly for the first time.

窒素分子のコインシデンス電子エネルギー損失スペクトルを測定し、解離的性質を持つ禁制2電子励起状態を明らかにした。

超伝導電子冷却とイオン蓄積リングを用い、ヘリウム水素分子イオンの4つの同位体の解離性再結合反応速度定数を超高分解能で測定し、多くの共鳴構造を見出した。共鳴構造を多チャンネル量子欠損理論を用いて解析した。

水素分子のコインシデンス電子エネルギー損失スペクトルを測定し、通常の電子エネルギー損失スペクトルとの比較から、光学的禁制超励起状態の解離の分岐比について議論した。

The electron energy-loss spectra of H(2) in coincidence with H(2p) formation have been measured in the range just above the dissociation limit of H(ls) + H(2p) at the incident electron energies of 30 and 150 eV and the scattering angle of 2 degrees, The ordinary energy-loss spectra at the same incident energies and scattering angle have also been measured. It is clearly seen that optically-allowed states dominate in the ordinary energy-loss spectra while optically-forbidden states contribute noticeably to the coincident energy-loss spectrum at the 30 eV incident energy. The forbidden states predissociating into H(1s) + H(2p) are assigned and the branching ratio of the predissociation. the intensity ratio of the coincident energy-loss spectrum to the corresponding ordinary one, is obtained. The predissociation pathways into H(ls) + H(2p) from those forbidden states are discussed in detail.

水素分子2電子励起状態のコインシデンス電子エネルギー損失スペクトルに見られる同位体効果を議論した。特に、未知の2電子励起状態であるF状態については、同位体効果から、Q2状態ではないかと結論付けた。

The state-resolved isotope effect an the cross sections of 2p atom formation via precursor doubly excited states of H-2 and D-2 is obtained at 80 eV incident electron energy and 3 degrees scattering angle by means of coincident electron-energy-loss spectroscopy as well as theoretical fits based on the reflection approximation and the survival probability. It turns out that the degree of the isotope effect depends strongly on the precursor doubly excited states and hence is a significant character of them. The origin of this dependence is discussed.