Study of the photoelectron and electron momentum spectra of cyclopentene using benchmark Dyson orbital theories

A complete study of the valence electronic structure and related electronic excitation properties of cyclopentene in its C(s) ground state geometry is presented. Ionization spectra obtained from this compound by means of photoelectron spectroscopy (He I and He II) and electron momentum spectroscopy have been analyzed in details up to electron binding energies of 30 eV using one-particle Green's function (1p-GF) theory along with the outer-valence (OVGF) and the third-order algebraic diagrammatic construction [ADC(3)] schemes. The employed geometries derive from DFT/B3LYP calculations in conjunction with the aug-cc-pVTZ basis set, and closely approach the structures inferred from experiments employing microwave spectroscopy or electron diffraction in the gas phase. The 1p-GF/ADC(3) calculations indicate that the orbital picture of ionization breaks down at electron binding energies larger than approximately 17 eV in the inner-valence region, and that the outer-valence 7a' orbital is also subject to a significant dispersion of the ionization intensity over shake-up states. This study confirms further the rule that OVGF pole strengths smaller than 0.85 foretell a breakdown of the orbital picture of ionization at the ADC(3) level. Spherically averaged (e, 2e) electron momentum distributions at an electron impact energy of 1200 eV that were experimentally inferred from an angular analysis of EMS intensities have been interpreted by comparison with accurate simulations employing ADC(3) Dyson orbitals. Very significant discrepancies were observed with momentum distributions obtained from several outer-valence ionization bands using standard Kohn-Sham orbitals.     

Study of the molecular structure, ionization spectrum, and electronic wave function of 1,3-butadiene using electron momentum spectroscopy and benchmark Dyson orbital theories

The scope of the present work is to reconcile electron momentum spectroscopy with elementary thermodynamics, and refute conclusions drawn by Saha et al. in J. Chem. Phys. 123, 124315 (2005) regarding fingerprints of the gauche conformational isomer of 1,3-butadiene in electron momentum distributions that were experimentally inferred from gas phase (e,2e) measurements on this compound [M. J. Brunger et al., J. Chem. Phys. 108, 1859 (1998)]. Our analysis is based on thorough calculations of one-electron and shake-up ionization spectra employing one-particle Green's function theory along with the benchmark third-order algebraic diagrammatic construction [ADC(3)] scheme. Accurate spherically averaged electron momentum distributions are correspondingly computed from the related Dyson orbitals. The ionization spectra and Dyson orbital momentum distributions that were computed for the trans-conformer of 1,3-butadiene alone are amply sufficient to quantitatively unravel the shape of all available experimental (e,2e) electron momentum distributions. A comparison of theoretical ADC(3) spectra for the s-trans and gauche energy minima with inner- and outer-valence high-resolution photoelectron measurements employing a synchrotron radiation beam [D. M. P. Holland et al., J. Phys. B 29, 3091 (1996)] demonstrates that the gauche structure is incompatible with ionization experiments in high-vacuum conditions and at standard temperatures. On the other hand, outer-valence Green's function calculations on the s-trans energy minimum form and approaching basis set completeness provide highly quantitative insights, within approximately 0.2 eV accuracy, into the available experimental one-electron ionization energies. At last, analysis of the angular dependence of relative (e,2e) ionization intensities nicely confirms the presence of one rather intense pi(-2) pi(*+1) satellite at approximately 13.1 eV in the ionization spectrum of the s-trans conformer.     

High resolution electron momentum spectroscopy of the valence orbitals of water

The development of a third-generation electron momentum spectrometer with significantly improved energy and momentum resolutions at Tsinghua University (ΔE = 0.45–0.68 eV, Δθ = ±0.53° and Δ? = ±0.84°) has enabled a reinvestigation of the valence orbital electron momentum distributions of H₂O with improved statistical accuracy. The measurements have been conducted at impact energies of 1200 eV and 2400 eV in order to check the validity of the plane wave impulse approximation. The obtained ionization spectra and electron momentum distributions have been compared with the results of computations carried out with Hartree Fock [HF] theory, density functional theory in conjunction with the standard B3LYP functional, one-particle Green’s function [1p-GF] theory along with the third-order algebraic diagrammatic construction scheme [ADC(3)], symmetry adapted cluster configuration interaction [SAC-CI] theory, and a variety of multi-reference [MR-SDCI, MR-RSPT2, MR-RSPT3] theories. The influence of the basis set on the computed momentum distributions has been investigated further, using a variety of basis sets ranging from 6-31G to the almost complete d-aug-cc-pV6Z basis set. A main issue in the present work pertains to a shake-up band of very weak intensity at 27.1 eV, of which the related momentum distribution was analyzed for the first time. The experimental evidences and the most thorough theoretical calculations demonstrate that this band borrows its ionization intensity from the 2a₁ orbital.     

Benchmark Dyson orbital study of the ionization spectrum and electron momentum distributions of ethanol in conformational equilibrium

An extensive study, throughout the valence region, of the electronic structure, ionization spectrum, and electron momentum distributions of ethanol is presented, on the ground of a model that focuses on a mixture of the gauche and anti conformers in their energy minimum form, using weight coefficients obtained from thermostatistical calculations that account for the influence of hindered rotations. The analysis is based on accurate calculations of valence one-electron and shakeup ionization energies and of the related Dyson orbitals, using one-particle Green's Function (1p-GF) theory in conjunction with the so-called third-order Algebraic Diagrammatic Construction scheme [ADC(3)]. The confrontation against available UPS (HeI) measurements indicates the presence in the spectral bands of significant conformational fingerprints at outer-valence ionization energies ranging from approximately 14 to approximately 18 eV. The shakeup onset is located at approximately 24 eV, and a shoulder at approximately 14.5 eV in the He I spectrum can be specifically ascribed to the minor anti (C(s)) conformer fraction. Thermally and spherically averaged Dyson orbital momentum distributions are computed for seven resolvable bands in model (e, 2e) ionization spectra at an electron impact energy of 1.2 keV. A comparison is made with results obtained from standard (B3LYP) Kohn-Sham orbitals and EMS measurements employing a high-resolution spectrometer of the third generation. The analysis is qualitatively in line with experiment and reveals a tremendously strong influence of the molecular conformation on the outermost electron momentum distributions. Quantitatively significant discrepancies with experiment can nonetheless be tentatively ascribed to strong dynamical disorder in the gas phase molecular structure.     

The band 12 issue in the electron momentum spectra of norbornane: a comparison with additional Green's Function calculations and ultraviolet photoemission measurements

In continuation of a recent study of the electronic structure of norbornane [J. Chem. Phys., 2004, 121, 10525] by means of electron momentum spectroscopy (EMS), we present Green's Function calculations of the ionization spectrum of this compound at the ADC(3) level using basis sets of varying quality, along with accurate evaluations at the CCSD(T) level of the vertical (26.5 eV) and adiabatic (22.1 eV) double ionization thresholds under C(2v) symmetry. The obtained results are compared with newly recorded ultraviolet photoemission spectra (UPS), up to binding energies of 40 eV. The theoretical predictions are entirely consistent with experiment and indicate that, in a vertical depiction of ionization, shake-up states at binding energies larger than approximately 26.5 eV tend to decay via emission of a second electron in the continuum. A band of s-type symmetry that has been previously seen at approximately 25 eV in the electron impact ionization spectra of norbornane is entirely missing in the UPS measurements and theoretical ADC(3) spectra. With regard to these results and to the time scales characterizing electron-electron interactions in EMS (10(-17) s) as compared with that (10(-13) s) of photon-electron interactions in UPS, and considering the p-type symmetry of the electron momentum distributions for the nearest 1b(1) and 1b(2) orbitals, this additional band can certainly not be due to adiabatic double ionization processes starting from the ground electronic state of norbornane, or to exceptionally strong vibronic coupling interactions between cationic states derived from ionization of the latter orbitals. It is therefore tentatively ascribed to autoionization processes via electronically excited and possibly dissociating states.     

Probing molecular conformations in momentum space: the case of n-pentane

A comprehensive study, throughout the valence region, of the electronic structure and electron momentum density distributions of the four conformational isomers of n-pentane is presented. Theoretical (e,2e) valence ionization spectra at high electron impact energies (1200 eV+electron binding energy) and at azimuthal angles ranging from 0 degrees to 10 degrees in a noncoplanar symmetric kinematical setup are generated according to the results of large scale one-particle Green's function calculations of Dyson orbitals and related electron binding energies, using the third-order algebraic-diagrammatic construction [ADC(3)] scheme. The results of a focal point analysis (FPA) of relative conformer energies [A. Salam and M. S. Deleuze, J. Chem. Phys. 116, 1296 (2002)] and improved thermodynamical calculations accounting for hindered rotations are also employed in order to quantitatively evaluate the abundance of each conformer in the gas phase at room temperature and reliably predict the outcome of experiments on n-pentane employing high resolution electron momentum spectroscopy. Comparison with available photoelectron measurements confirms the suggestion that, due to entropy effects, the trans-gauche (tg) conformer strongly dominates the conformational mixture characterizing n-pentane at room temperature. Our simulations demonstrate therefore that experimental measurements of (e,2e) valence ionization spectra and electron momentum distributions would very consistently and straightforwardly image the topological changes and energy variations that molecular orbitals undergo due to torsion of the carbon backbone. The strongest fingerprints for the most stable conformer (tt) are found for the electron momentum distributions associated with ionization channels at the top of the inner-valence region, which sensitively image the development of methylenic hyperconjugation in all-staggered n-alkane chains.     

Theoretical fine spectroscopy with symmetry-adapted-cluster configuration-interaction method: outer- and inner-valence ionization spectra of furan, pyrrole, and thiophene

Theoretical fine spectroscopy has been performed for the valence ionization spectra of furan, pyrrole, and thiophene with the symmetry-adapted-cluster configuration-interaction general-R method. The present method described that the pi(1) state interacts with the pi(3) (-2)pi*, pi(2) (-2)pi*, and pi(2) (-1)pi(3) (-1)pi* shake-up states providing the split peaks and the outer-valence satellites, both of which are in agreement with the experiments. The intensity distributions were analyzed in detail for the inner-valence region. In particular, for furan, theoretical intensities were successfully compared with the intensity measured by the electron momentum spectroscopy. The interactions of the 3b(2) and 5a(1) states with the shake-up states were remarkable for furan and pyrrole, while the 4b(2) state of thiophene had relatively large intensity.     

Deprotonated cytosine anions: a theoretical prediction of photoelectron spectra

Predictions on the photoelectron spectra of deprotonated cytosine anions (cytosinate, Cye(-)) have been made with ab initio electron propagator methods. Two imino-oxo forms are most stable, but four other isomers have energies within 10 kcal/mol. The first vertical electron detachment energies (VEDEs) for the three most stable Cye(-) isomers are approximately 3.4 eV. Imino-oxy VEDEs are about 0.3 eV smaller. For each anion, the lowest VEDE corresponds to a pi Dyson orbital. The order of higher final states is changed when relaxation and correlation effects are considered. Considerable mixing between lone-pair and bonding lobes occurs in the sigma Dyson orbitals.     

Imaging momentum orbital densities of conformationally versatile molecules: a benchmark theoretical study of the molecular and electronic structures of dimethoxymethane

The main purpose of the present work is to predict from benchmark many-body quantum mechanical calculations the results of experimental studies of the valence electronic structure of dimethoxymethane employing electron momentum spectroscopy, and to establish once and for all the guidelines that should systematically be followed in order to reliably interpret the results of such experiments on conformationally versatile molecules. In a first step, accurate calculations of the energy differences between stationary points on the potential energy surface of this molecule are performed using Hartree-Fock (HF) theory and post-HF treatments of improving quality (MP2, MP3, CCSD, CCSD(T), along with basis sets of increasing size. This study focuses on the four conformers of this molecule, namely the trans-trans (TT), trans-gauche (TG), gauche-gauche (G+G+), and gauche-gauche (G+G-) structures, belonging to the C2v, C1, C2, and Cs symmetry point groups, respectively. A focal point analysis supplemented by suited extrapolations to the limit of asymptotically complete basis sets is carried out to determine how the conformational energy differences at 0 K approach the full CI limit. In a second step, statistical thermodynamics accounting for hindered rotations is used to calculate Gibbs free energy corrections to the above energy differences, and to evaluate the abundance of each conformer in the gas phase. It is found that, at room temperature, the G+G+ species accounts for 96% of the conformational mixture characterizing dimethoxymethane. In a third step, the valence one-electron and shake-up ionization spectrum of dimethoxymethane is analyzed according to calculations on the G+G+ conformer alone by means of one-particle Green's function [1p-GF] theory along with the benchmark third-order algebraic diagrammatic construction [ADC(3)] scheme. A complete breakdown of the orbital picture of ionization is noted at electron binding energies above 22 eV. A comparison with available (e,2e) ionization spectra enables us to identify specific fingerprints of through-space orbital interactions associated with the anomeric effect. At last, based on our 1p-GF/ADC(3) assignment of spectral bands, accurate and spherically averaged (e,2e) electron momentum distributions at an electron impact energy of 1200 eV are computed from the related Dyson orbitals. Very significant discrepancies are observed with momentum distributions obtained for several outer-valence levels using standard Kohn-Sham orbitals.     

Investigation into the valence electronic structure of norbornene using electron momentum spectroscopy, Green's function, and density functional theories

Results of a study of the valence electronic structure of norbornene (C(7)H(10)), up to binding energies of 30 eV, are reported. Experimental electron momentum spectroscopy (EMS) and theoretical Green's function and density functional theory approaches were utilized in this investigation. A stringent comparison between the electron momentum spectroscopy and theoretical orbital momentum distributions found that, among the tested models, the combination of the Becke-Perdew functional and a polarized valence basis set of triple-zeta quality provides the best representation of the electron momentum distributions for all 19 valence orbitals of norbornene. This experimentally validated model was then used to extract other molecular properties of norbornene (geometry, infrared spectrum). When these calculated properties are compared to corresponding results from independent measurements, reasonable agreement is typically found. Due to the improved energy resolution, EMS is now at a stage to very finely image the effective topology of molecular orbitals at varying distances from the molecular center, and the way the individual atomic components interact with each other, often in excellent agreement with theory. This will be demonstrated here. Green's Function calculations employing the third-order algebraic diagrammatic construction scheme indicate that the orbital picture of ionization breaks down at binding energies larger than about 22 eV. Despite this complication, they enable insights within 0.2 eV accuracy into the available ultraviolet emission and newly presented (e,2e) ionization spectra. Finally, limitations inherent to calculations of momentum distributions based on Kohn-Sham orbitals and employing the vertical depiction of ionization processes are emphasized, in a formal discussion of EMS cross sections employing Dyson orbitals.     

Electron momentum spectroscopy of sulphurhexafluoride

The SF₆ molecule has been studied using high-resolution electron momentum spectroscopy [EMS], at a total energy of 1200 eV and using non-coplanar symmetric kinematics. Binding-energy spectra ranging up to 62 eV were measured at out of plane azimuthal angles from 0° to 28°, and in the outer-valence region from 0° to 34°, corresponding to target electron momenta from about 0.1–2.8 au. The binding-energy spectra and electron momentum distributions obtained for the valence orbitals are compared with the results of Green function calculations for the ionization energies and their corresponding pole strengths and the spherically averaged momentum distributions obtained from the SCF wavefunction on which the Green function calculations are based. The SCF basis includes d components on both S and F atoms. In the outer-valence region, where the one-particle picture holds for the ionization process, there is very good agreement between the theoretical energies and pole strengths and the measured ones, but the orbital momentum distributions are given poorly by the SCF wavefunctions. The measured momentum distributions are significantly higher at low momentum (< 1 au), particularly for the 1t_2u and 3e_g orbitals. In the inner-valence region a substantial splitting of the lines occurs, which is only predicted in a qualitative way. The SCF momentum distribution for the 2e_g orbital is in poor agreement with the data, whereas that of the 3t_1u orbital is in very good agreement with the measurements.     

Norbornane: an investigation into its valence electronic structure using electron momentum spectroscopy, and density functional and Green's function theories

We report on the results of an exhaustive study of the valence electronic structure of norbornane (C(7)H(12)), up to binding energies of 29 eV. Experimental electron momentum spectroscopy and theoretical Green's function and density functional theory approaches were all utilized in this investigation. A stringent comparison between the electron momentum spectroscopy and theoretical orbital momentum distributions found that, among all the tested models, the combination of the Becke-Perdew functional and a polarized valence basis set of triple-zeta quality provides the best representation of the electron momentum distributions for all of the 20 valence orbitals of norbornane. This experimentally validated quantum chemistry model was then used to extract some chemically important properties of norbornane. When these calculated properties are compared to corresponding results from other independent measurements, generally good agreement is found. Green's function calculations with the aid of the third-order algebraic diagrammatic construction scheme indicate that the orbital picture of ionization breaks down at binding energies larger than 22.5 eV. Despite this complication, they enable insights within 0.2 eV accuracy into the available ultraviolet photoemission and newly presented (e,2e) ionization spectra, except for the band associated with the 1a(2) (-1) one-hole state, which is probably subject to rather significant vibronic coupling effects, and a band at approximately 25 eV characterized by a momentum distribution of "s-type" symmetry, which Green's function calculations fail to reproduce. We note the vicinity of the vertical double ionization threshold at approximately 26 eV.     

Electronic and cationic states of 2-methylpropene (isobutene) studied by VUV absorption,scattered electron spectroscopy and AB initio multireference configuration interaction calculations

VUV (6.2–9 eV) and electron scattering spectra (1–9 eV) have been recorded for 2-methylpropene (isobutene). Also, electronic states of the molecule, including the ground state and cationic states, have been investigated using ab initio multi-reference configuration interaction calculations. Some Koopmans-type in the UV photoelectron spectrum are reassigned and a number of shake-up states computed. In the electronic spectrum, Rydberg excited have been assigned and a second valence excited state (σ π*) located within about 1 eV of the V(ππ*) state. The experiments show, and theory confirms, that the Rydberg R(π3s) state has a positive electron affinity. Some interesting correlations between ionisation energies, energies of shake-up state electronic excitation energies are identified.     

Negative ions of nitroethane and its clusters

Valence and dipole-bound negative ions of the nitroethane (NE) molecule and its clusters are studied using photoelectron spectroscopy (PES), Rydberg electron transfer (RET) techniques, and ab initio methods. Valence adiabatic electron affinities (EA(a)s) of NE, C(2)H(5)NO(2), and its clusters, (C(2)H(5)NO(2))(n), n=2-5, are estimated using vibrationally unresolved PES to be 0.3+/-0.2 eV (n=1), 0.9+/-0.2 eV (n=2), 1.5+/-0.2 eV (n=3), 1.9+/-0.2 eV (n=4), and 2.1+/-0.2 eV (n=5). These energies were then used to determine stepwise anion-neutral solvation energies and compared with previous literature values. Vertical detachment energies for (C(2)H(5)NO(2))(n)(-) were also measured to be 0.92+/-0.10 eV (n=1), 1.63+/-0.10 eV (n=2), 2.04+/-0.10 eV (n=3), and 2.3+/-0.1 eV (n=4). RET experiments show that Rydberg electrons can be attached to NE both as dipole-bound and valence bound anion states. The results are similar to those found for nitromethane (NM), where it was argued that the diffuse dipole state act as a "doorway state" to the more tightly bound valence anion. Using previous models for relating the maximum in the RET dependence of the Rydberg effective principle number n(max)(*), the dipole-bound electron affinity is predicted to be approximately 25 meV. However, a close examination of the RET cross section data for NE and a re-examination of such data for NM finds a much broader dependence on n(*) than is seen for RET in conventional dipole bound states and, more importantly, a pronounced [l] dependence is found in n(max)(*) (n(max)(*) increases with [l]). Ab initio calculations agree well with the experimental results apart from the vertical electron affinity value associated with the dipole bound state which is predicted to be 8 meV. Moreover, the calculations help to visualize the dramatic difference in the distributions of the excess electron for dipole-bound and valence states, and suggest that NE clusters form only anions where the excess electron localizes on a single monomer.     

Ion-pair dissociation of N2O in the 16.25-16.41 eV: dynamics and electronic structure

The ion-pair dissociation dynamics of N(2)O -->(XUV) N(2)(+)(X (2)Sigma(g)(+), v) + O(-)((2)P(j)) at 16.248, 16.271, 16.389, and 16.411 eV have been studied using the velocity map imaging method and tunable XUV laser. The electronic structures of the ion-pair states have been studied by employing the ab initio quantum chemical calculation. The translational energy distributions and the angular distributions of the photofragments have been measured. The results show that about 40% of available energies are transformed into the translational energies, and the first excited vibrational states are populated most strongly for all four excitation energies. The anisotropy parameters beta are approximately 1. The ab initio calculations at the level of CASSCF6-311++g(3df) show that the equilibrium geometries of the ion-pair states are nonlinear with bond lengths R(N-N) = 1.10 A, R(N-O) = 2.15 A, and bond angle N-N-O = 103 degrees, respectively. The ion-pair states are formed by electron migration from the bonding sigma orbital of N[triple bond]N to the antibonding sigma orbital localized primarily on the O atom. Combining the experimental and theoretical results, it is concluded that the ion-pair dissociation occurs via predissociation of Rydberg states with (1)Sigma(+) symmetry, which converges to the ion-core N(2)O(+)(A (2)Sigma(+)).     

Electron momentum spectroscopy of trisubstituted amines: The valence shell orbitals of triethylamine

The ionization potentials of the valence shell orbitals (up to 40 eV) of triethylamine have been measured by means of the binary (e,2e) technique. Satellite structure, due to transitions to ionic excited states, has been observed in the outer valence shell for binding energies larger than 15 eV. The electron momentum distributions of the valence orbitals have been measured on ionization peaks corresponding to main and satellite transitions. Results are compared with SCF calculations. The electron momentum distribution of the most external orbital, formed mostly by the N 2p lone pair, is discussed in detail.     

Coexistence of 1,3-butadiene conformers in ionization energies and Dyson orbitals

The minimum-energy structures on the torsional potential-energy surface of 1,3-butadiene have been studied quantum mechanically using a range of models including ab initio Hartree-Fock and second-order M?ller-Plesset theories, outer valence Green's function, and density-functional theory with a hybrid functional and statistical average orbital potential model in order to understand the binding-energy (ionization energy) spectra and orbital cross sections observed by experiments. The unique full geometry optimization process locates the s-trans-1,3-butadiene as the global minimum structure and the s-gauche-1,3-butadiene as the local minimum structure. The latter possesses the dihedral angle of the central carbon bond of 32.81 degrees in agreement with the range of 30 degrees-41 degrees obtained by other theoretical models. Ionization energies in the outer valence space of the conformer pair have been obtained using Hartree-Fock, outer valence Green's function, and density-functional (statistical average orbital potentials) models, respectively. The Hartree-Fock results indicate that electron correlation (and orbital relaxation) effects become more significant towards the inner shell. The spectroscopic pole strengths calculated in the Green's function model are in the range of 0.85-0.91, suggesting that the independent particle picture is a good approximation in the present study. The binding energies from the density-functional (statisticaly averaged orbital potential) model are in good agreement with photoelectron spectroscopy, and the simulated Dyson orbitals in momentum space approximated by the density-functional orbitals using plane-wave impulse approximation agree well with those from experimental electron momentum spectroscopy. The coexistence of the conformer pair under the experimental conditions is supported by the approximated experimental binding-energy spectra due to the split conformer orbital energies, as well as the orbital momentum distributions of the mixed conformer pair observed in the orbital cross sections of electron momentum spectroscopy.     

Theoretical and experimental investigations of the electronic Rydberg states of diazomethane: assignments and state interactions

The electronic states of diazomethane in the region 3.00-8.00 eV have been characterized by ab initio calculations, and electronic transitions in the region 6.32-7.30 eV have been examined experimentally using a combination of 2 + 1 REMPI spectroscopy and photoelectron imaging in a molecular beam. In the examined region, three Rydberg states of 3p character contribute to the transitions, 2(1)A2(3p(y) <-- pi), 2(1)B1(3p(z) <-- pi), and 3(1)A1(3p(x) <-- pi). The former two states are of mostly pure Rydberg character and exhibit a resolved K structure, whereas the 3(1)A1(3p(x) <-- pi) state is mixed with the valence 2(1)A1(pi* <-- pi) state, which is unbound and is strongly predissociative. Analyses of photoelectron kinetic energy distributions indicate that the ground vibrational level of the 2(1)B1(3p(z)) state is mixed with the 2(1)A2(3p(y)) nu(9) level, which is of B1 vibronic symmetry. The other 2(1)A2(3p(y)) vibronic states exhibit pure Rydberg character, generating ions in single vibrational levels. The photoelectron spectra of the 3(1)A1(3p(x) <-- pi) state, on the other hand, give rise to many states of the ion as a result of strong mixing with the valence state, as evidenced also in the ab initio calculations. The equilibrium geometries of the electronic states of neutral diazomethane were calculated by CCSD(T), using the cc-pVTZ basis, and by B3LYP, using the 6-311G(2df,p) basis. Geometry and frequencies of the ground state of the cation were calculated by CCSD(T)/cc-pVTZ, using the unrestricted (UHF) reference. Vertical excitation energies were calculated using EOM-CCSD/6-311(3+,+)G* at the B3LYP optimized geometry. The theoretical results show that the 2(1)A2(3p(y) <-- pi) and 2(1)B1(3p(z) <-- pi) states have geometries similar to the ion, which has C(2v) symmetry, with slight differences due to the interactions of the electron in the 3p orbital with the nuclei charge distributions. The geometry of the 3(1)A1(3p(x) <-- pi) state is quite different and has Cs symmetry. The experimental and theoretical results agree very well, both in regard to excitation energies and to vibrational modes of the ion.     

丙烷分子的价轨道(2b2)电子的动量分布测量

电子动量谱学（EMS）是在原子、分子和固体物理中研究电子结构的一种强有力的工具，它基于运动学条件完全确定的（e，2e）碰撞电离反应[1-3]．本文报告用高分辨电子动量谱仪首次测量得到丙烷门3H8）分子的价轨道电子（252）的动量分布·丙烷（C3Hs）价轨道电子的动量分布实验是     

C1s and O1s photoelectron satellite spectra of CO with symmetry-dependent vibrational excitations

The photoelectron shake-up satellite spectra that accompany the C1s and O1s main lines of carbon monoxide have been studied by a combination of high-resolution x-ray photoelectron spectroscopy and accurate ab initio calculations. The symmetry-adapted cluster-expansion configuration-interaction general-R method satisfactorily reproduces the satellite spectra over a wide energy region, and the quantitative assignments are proposed for the 16 and 12 satellite bands for C1s and O1s spectra, respectively. Satellite peaks above the pi(-1)pi(*) transitions are mainly assigned to the Rydberg excitations accompanying the inner-shell ionization. Many shake-up states, which interact strongly with three-electron processes such as pi(-2)pi(*2) and n(-2)pi(*2), are calculated in the low-energy region, while the continuous Rydberg excitations are obtained with small intensities in the higher-energy region. The vibrational structures of low-lying shake-up states have been examined for both C1s and O1s ionizations. The vibrational structures appear in the low-lying C1s satellite states, and the symmetry-dependent angular distributions for the satellite emission have enabled the Sigma and Pi symmetries to be resolved. On the other hand, the potential curves of the low-lying O1s shake-up states are predicted to be weakly bound or repulsive.