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Xiangjun Chen - One of the best experts on this subject based on the ideXlab platform.
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Vibrational effects on Electron Momentum distributions of outer valence orbitals of benzene
Chinese Physics B, 2020Co-Authors: Yu Zhang, Xu Shan, Shanshan Niu, Yaguo Tang, Yichun Wang, Xiangjun ChenAbstract:The outer valence Electron Momentum distributions of benzene are reinvestigated with theoretical calculations involving vibrational effects. The results are compared with recent experimental measurements[Phys. Rev. A 98, 042705(2018)]. The significant discrepancies between theories and experiments in previous works have now been interpreted quantitatively, indicating that the vibrational motion in benzene molecule has noticeable influence on its Electron Momentum distributions.
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Electron Momentum spectroscopy investigation on Electronic structure of iso-dichloroethylene valence shell
Chinese Journal of Chemical Physics, 2019Co-Authors: Yichun Wang, Xu Shan, Shanshan Niu, Yaguo Tang, Yu Zhang, Xiangjun ChenAbstract:Here an Electron Momentum spectroscopy study on the Electronic structure of valence shell of iso-dichloroethylene molecule is reported. The experiment is carried out with a binary (e, 2e) spectrometer at incident Electron energy of 1200 eV, employing noncoplanar symmetric arrangement. The binding energy spectra and Electron Momentum distributions (EMDs) of iso-dichloroethylene valence shell have been obtained. Theoretical EMDs are predicted with both Hartree-Fock and density functional theory methods, generally indicating good agreements with the measurement results. The interference effect is observed to significantly influence the EMDs of 2a2 and 5b2 Cl lone-pair orbitals.Here an Electron Momentum spectroscopy study on the Electronic structure of valence shell of iso-dichloroethylene molecule is reported. The experiment is carried out with a binary (e, 2e) spectrometer at incident Electron energy of 1200 eV, employing noncoplanar symmetric arrangement. The binding energy spectra and Electron Momentum distributions (EMDs) of iso-dichloroethylene valence shell have been obtained. Theoretical EMDs are predicted with both Hartree-Fock and density functional theory methods, generally indicating good agreements with the measurement results. The interference effect is observed to significantly influence the EMDs of 2a2 and 5b2 Cl lone-pair orbitals.
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Experimental and theoretical study of the valence Electronic structure of propane by Electron Momentum spectroscopy
Journal of Electron Spectroscopy and Related Phenomena, 2018Co-Authors: Shanshan Niu, Xu Shan, Yaguo Tang, Zhaohui Liu, Xiangjun ChenAbstract:Abstract Binding energy spectra and Electron Momentum profiles for the valence orbitals of propane have been measured at Electron impact energy of 1.2 keV plus binding energy. The experimental Electron Momentum profiles (XMPs) are compared with the theoretical ones calculated for the relevant molecular orbitals using density functional theory. The calculation taking molecular vibration into account can well explain high intensity of the XMPs at low Momentum region for 1a2 and 3b2 outer valence orbitals, showing a noticeable influence of the vibrational effect on orbital Electron Momentum profiles. For the inner valence orbitals, an attempt to reveal the interference effect or bond oscillation has been presented through the ratios of Electron Momentum profiles for the bonding and anti-bonding molecular orbitals. The observation of oscillation structures indicates the presence of interference effects.
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High Resolution Electron Momentum Spectroscopy Study on Ethanol: Orbital Electron Momentum Distributions for Individual Conformers
Chinese Journal of Chemical Physics, 2016Co-Authors: Xu Shan, Shanshan Niu, Yaguo Tang, Xiangjun ChenAbstract:The outer-valence binding energy spectra of ethanol in the energy range of 9–21 eV are measured by a high-resolution Electron Momentum spectrometer at an impact energy of 2.5 keV plus the binding energy. The Electron Momentum distributions for the ionization peaks corresponding to the outer-valence orbitals are obtained by deconvoluting a series of azimuthal angular correlated binding energy spectra. Comparison is made with the theoretical calculations for two conformers, trans and gauche, coexisting in the gas phase of ethanol at the level of B3LYP density functional theory with aug-cc-pVTZ basis sets. It is found that the measured Electron Momentum distributions for the peaks at 14.5 and 15.2 eV are in good agreement with the theoretical Electron Momentum distributions for the molecular orbitals of individual conformers (i.e., 8a′ of trans and 9a of gauche), but not in accordance with the thermally averaged ones. It demonstrates that the high-resolution Electron Momentum spectrometer, by inspecting the ...
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Imaging molecular geometry with Electron Momentum spectroscopy
Scientific reports, 2016Co-Authors: Enliang Wang, Xu Shan, Shanshan Niu, Yaguo Tang, Qiguo Tian, Jing Yang, Maomao Gong, Xiangjun ChenAbstract:Electron Momentum spectroscopy is a unique tool for imaging orbital-specific Electron density of molecule in Momentum space. However, the molecular geometry information is usually veiled due to the single-centered character of Momentum space wavefunction of molecular orbital (MO). Here we demonstrate the retrieval of interatomic distances from the multicenter interference effect revealed in the ratios of Electron Momentum profiles between two MOs with symmetric and anti-symmetric characters. A very sensitive dependence of the oscillation period on interatomic distance is observed, which is used to determine F-F distance in CF4 and O-O distance in CO2 with sub-Angstrom precision. Thus, using one spectrometer, and in one measurement, the Electron density distributions of MOs and the molecular geometry information can be obtained simultaneously. Our approach provides a new robust tool for imaging molecules with high precision and has potential to apply to ultrafast imaging of molecular dynamics if combined with ultrashort Electron pulses in the future.
Masahiko Takahashi - One of the best experts on this subject based on the ideXlab platform.
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Electron Momentum spectroscopy study on the valence Electronic structure of methyl formate.
The Journal of chemical physics, 2019Co-Authors: N Watanabe, Kimihiro Sato, Masahiko TakahashiAbstract:We report an Electron Momentum spectroscopy study on methyl formate. A symmetric noncoplanar (e, 2e) experiment has been performed at an incident Electron energy of 1.2 keV and Electron Momentum profiles of the valence orbitals have been obtained. On the basis of the result, assignments of the 10a'-1 and 1a″-1 bands have been made to resolve a contradiction between photoElectron spectroscopy and Penning ionization Electron spectroscopy studies. Comparisons between experiment and theory reveal that the influence of the molecular vibration has to be taken into account for a proper understanding of the Electron Momentum profiles. Contributions of individual vibrational normal modes have also been investigated in detail by means of the harmonic analytical quantum mechanical approach.
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Influence of molecular vibrations on the valence Electron Momentum distributions of adamantane
The Journal of Chemical Physics, 2017Co-Authors: Filippo Morini, Michael S. Deleuze, N Watanabe, Masataka Kojima, Masahiko TakahashiAbstract:We report an Electron Momentum spectroscopy study of vibrational effects on the Electron Momentum distributions of the outer valence orbitals of adamantane (C10H16). The symmetric noncoplanar (e, 2e) experiment has been carried out at an incident Electron energy of 1.2 keV. Furthermore, theoretical calculations of the Electron Momentum distributions with vibrational effects being involved have been performed using the harmonic analytical quantum mechanical and Born-Oppenheimer molecular dynamics approaches. In spite of the complex nature of the vibrational structure of this large molecule, both approaches provide overall quantitative insights into the results of the experiment. Comparisons between experiment and theory have shown that ground state nuclear dynamics appreciably affects the Momentum profiles of the 7t2, {2t1 + 3e}, and {5t2 + 5a1} orbitals. It has been demonstrated that changes in the Momentum profiles are mainly due to the vibrational motions associated with the CH bonds.
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EMS study of vibrational effects on Electron Momentum distributions of C2H4 and CH2F2
Journal of Physics: Conference Series, 2015Co-Authors: N Watanabe, Masakazu Yamazaki, Masahiko TakahashiAbstract:We report an Electron Momentum spectroscopy study of vibrational effects on the Electron Momentum distributions for the outer valence orbitals of C2H4 and CH2F2. The symmetric noncoplanar (e,2e) experiment has been conducted at impact energy of 1.2 keV. Furthermore, a theoretical method of calculating Electron Momentum distributions has been developed with vibrational effects being involved. The experimental and theoretical results for these molecules strongly suggest that vibrational effects on Electron Momentum distributions tend to be appreciable for non-total symmetry molecular orbitals delocalized over some equivalent CH-bond sites.
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Vibrational effects on valence Electron Momentum distributions of ethylene
Journal of Chemical Physics, 2014Co-Authors: N Watanabe, Masakazu Yamazaki, Masahiko TakahashiAbstract:We report an Electron Momentum spectroscopy study of vibrational effects on the Electron Momentum distributions for the outer valence orbitals of difluoromethane (CH2F2). The symmetric noncoplanar (e,2e) experiment has been performed at an incident Electron energy of 1.2 keV. Furthermore, a theoretical calculation of the Electron Momentum distributions of the CH2F2 molecule has been carried out with vibrational effects being involved. It is shown from comparisons between experiment and theory that it is essential to take into account influences of the CH2 asymmetric stretching and CH2 rocking vibrational modes for a proper understanding of the Electron Momentum distribution of the 2b1 orbital having the CH-bonding character. The results of CH2F2and additional theoretical calculations for (CH3)2O and H2CO molecules strongly suggest that vibrational effects on Electron Momentum distributions tend to be appreciable for non-total symmetry molecular orbitals delocalized over some equivalent CH-bond sites.
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Vibrational effects on valence Electron Momentum distributions of ethylene.
The Journal of chemical physics, 2012Co-Authors: N Watanabe, Masakazu Yamazaki, Masahiko TakahashiAbstract:We report an Electron Momentum spectroscopy study of vibrational effects on the Electron Momentum distributions for the outer valence orbitals of ethylene (C(2)H(4)). The symmetric noncoplanar (e,2e) experiment has been conducted at an impact energy of 1.2 keV. Furthermore, a theoretical method of calculating Electron Momentum distributions for polyatomic molecules has been developed with vibrational effects being involved. It is shown from comparisons between experiment and theory that taking into account effects of the CH(2) asymmetric stretching and CH(2) rocking vibrational modes of C(2)H(4) is essential for a proper understanding of the Electron Momentum distribution of the 1b(3g) molecular orbital.
Chuangang Ning - One of the best experts on this subject based on the ideXlab platform.
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The Jahn-Teller effect in the Electron Momentum spectroscopy of ammonia.
The Journal of chemical physics, 2012Co-Authors: Jing Zhu, Jing-kang Deng, Y R Miao, Chuangang NingAbstract:The 1e and 3a(1) bands of the ammonia molecule have been studied using the high-resolution Electron Momentum spectroscopy at impact energies of 1200 and 600 eV. Several slices of 1e and 3a(1) bands in the different binding energy ranges were selected, and their Electron-Momentum distributions were carefully compared. The discernable difference among the distributions of the selected slices of the 1e band shows that the Jahn-Teller effect indeed influences the Electron Momentum distribution of the 1e orbital of ammonia.
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High-resolution Electron-Momentum spectroscopy of the valence orbitals of the iodine molecule
Physical Review A, 2012Co-Authors: J. S. Zhu, J. K. Deng, Chuangang NingAbstract:The valence orbitals of the iodine molecule (I2) have been studied using the high-resolution Electron-Momentum spectroscopy at impact energies of 1200 and 600 eV. Experimental Momentum distributions of outer valence orbitals were compared with the nonrelativistic, scalar relativistic, and spin-orbital relativistic calculations, as well as the relativistic pseudopotential calculation. The experimental cross-section ratios of 8J 3/2 g to 17J 1/2 g , 8J 3/2 u to 16J 1/2 u , and the Electron-Momentum profiles of orbital 16J 1/2 g clearly manifested the relativistic effects. In the inner valence region, the symmetry-adapted-cluster configuration-interaction theory was used to interpret the ionization spectrum and the Electron-Momentum distributions.
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vibrational effects on the Electron Momentum distributions of valence orbitals of formamide
Journal of Chemical Physics, 2012Co-Authors: Y R Miao, Jing-kang Deng, Chuangang NingAbstract:The ionization energy spectra and Electron Momentum distributions of formamide were investigated using the high-resolution Electron Momentum spectrometer in combination with high level calculations. The observed ionization energy spectra and Electron Momentum distributions were interpreted using symmetry adapted cluster-configuration interaction theory, outer valence Green function, and DFT-B3LYP methods. The ordering of 10a′ and 2a″ orbitals of formamide was assigned unambiguously by comparing the experimental Electron Momentum distributions with the corresponding theoretical results, i.e., 10a′ has a lower binding energy. In addition, it was found that the low-frequency wagging vibration of the amino group at room temperature has noticeable effects on the Electron Momentum distributions. The equilibrium-nuclear-positions-approximation, which was widely used in Electron Momentum spectroscopy, is not accurate for formamide molecule. The calculations based on the thermal average can evidently improve the a...
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high resolution Electron Momentum spectroscopy of the valence orbitals of water
Chemical Physics, 2008Co-Authors: Chuangang Ning, S.f. Zhang, Y.r. Huang, J. K. Deng, Balázs Hajgató, Stefan Knippenberg, Michael S. DeleuzeAbstract:Abstract 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 Δϕ = ±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.
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probing dyson orbitals with green s function theory and Electron Momentum spectroscopy
Chemical Physics Letters, 2006Co-Authors: Chuangang Ning, S.f. Zhang, J. K. Deng, G L Su, Stefan Knippenberg, Michael S. DeleuzeAbstract:Abstract Results of an experimental study of the valence Electronic structure of difluoromethane employing high-resolution Electron Momentum Spectroscopy with various impact energies are reported. One-particle Green’s Function theory is utilized, for the first time, for computing accurate spherically averaged Electron Momentum distributions. These are derived from Dyson orbitals obtained using the third-order Algebraic Diagrammatic Construction (ADC(3)) scheme. The corresponding eigen-energies also accurately reproduce the (e, 2e) ionization spectrum. Shortcomings of empirical analyses of (e, 2e) experiments based on Kohn–Sham orbitals and eigen-energies are comparatively discussed. A failure of the target Hartree-Fock approximation is noted for the Momentum distribution pertaining to the 1b 1 + 3b 2 + 5a 1 levels.
Xu Shan - One of the best experts on this subject based on the ideXlab platform.
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Vibrational effects on Electron Momentum distributions of outer valence orbitals of benzene
Chinese Physics B, 2020Co-Authors: Yu Zhang, Xu Shan, Shanshan Niu, Yaguo Tang, Yichun Wang, Xiangjun ChenAbstract:The outer valence Electron Momentum distributions of benzene are reinvestigated with theoretical calculations involving vibrational effects. The results are compared with recent experimental measurements[Phys. Rev. A 98, 042705(2018)]. The significant discrepancies between theories and experiments in previous works have now been interpreted quantitatively, indicating that the vibrational motion in benzene molecule has noticeable influence on its Electron Momentum distributions.
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Electron Momentum spectroscopy investigation on Electronic structure of iso-dichloroethylene valence shell
Chinese Journal of Chemical Physics, 2019Co-Authors: Yichun Wang, Xu Shan, Shanshan Niu, Yaguo Tang, Yu Zhang, Xiangjun ChenAbstract:Here an Electron Momentum spectroscopy study on the Electronic structure of valence shell of iso-dichloroethylene molecule is reported. The experiment is carried out with a binary (e, 2e) spectrometer at incident Electron energy of 1200 eV, employing noncoplanar symmetric arrangement. The binding energy spectra and Electron Momentum distributions (EMDs) of iso-dichloroethylene valence shell have been obtained. Theoretical EMDs are predicted with both Hartree-Fock and density functional theory methods, generally indicating good agreements with the measurement results. The interference effect is observed to significantly influence the EMDs of 2a2 and 5b2 Cl lone-pair orbitals.Here an Electron Momentum spectroscopy study on the Electronic structure of valence shell of iso-dichloroethylene molecule is reported. The experiment is carried out with a binary (e, 2e) spectrometer at incident Electron energy of 1200 eV, employing noncoplanar symmetric arrangement. The binding energy spectra and Electron Momentum distributions (EMDs) of iso-dichloroethylene valence shell have been obtained. Theoretical EMDs are predicted with both Hartree-Fock and density functional theory methods, generally indicating good agreements with the measurement results. The interference effect is observed to significantly influence the EMDs of 2a2 and 5b2 Cl lone-pair orbitals.
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Experimental and theoretical study of the valence Electronic structure of propane by Electron Momentum spectroscopy
Journal of Electron Spectroscopy and Related Phenomena, 2018Co-Authors: Shanshan Niu, Xu Shan, Yaguo Tang, Zhaohui Liu, Xiangjun ChenAbstract:Abstract Binding energy spectra and Electron Momentum profiles for the valence orbitals of propane have been measured at Electron impact energy of 1.2 keV plus binding energy. The experimental Electron Momentum profiles (XMPs) are compared with the theoretical ones calculated for the relevant molecular orbitals using density functional theory. The calculation taking molecular vibration into account can well explain high intensity of the XMPs at low Momentum region for 1a2 and 3b2 outer valence orbitals, showing a noticeable influence of the vibrational effect on orbital Electron Momentum profiles. For the inner valence orbitals, an attempt to reveal the interference effect or bond oscillation has been presented through the ratios of Electron Momentum profiles for the bonding and anti-bonding molecular orbitals. The observation of oscillation structures indicates the presence of interference effects.
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High Resolution Electron Momentum Spectroscopy Study on Ethanol: Orbital Electron Momentum Distributions for Individual Conformers
Chinese Journal of Chemical Physics, 2016Co-Authors: Xu Shan, Shanshan Niu, Yaguo Tang, Xiangjun ChenAbstract:The outer-valence binding energy spectra of ethanol in the energy range of 9–21 eV are measured by a high-resolution Electron Momentum spectrometer at an impact energy of 2.5 keV plus the binding energy. The Electron Momentum distributions for the ionization peaks corresponding to the outer-valence orbitals are obtained by deconvoluting a series of azimuthal angular correlated binding energy spectra. Comparison is made with the theoretical calculations for two conformers, trans and gauche, coexisting in the gas phase of ethanol at the level of B3LYP density functional theory with aug-cc-pVTZ basis sets. It is found that the measured Electron Momentum distributions for the peaks at 14.5 and 15.2 eV are in good agreement with the theoretical Electron Momentum distributions for the molecular orbitals of individual conformers (i.e., 8a′ of trans and 9a of gauche), but not in accordance with the thermally averaged ones. It demonstrates that the high-resolution Electron Momentum spectrometer, by inspecting the ...
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Imaging molecular geometry with Electron Momentum spectroscopy
Scientific reports, 2016Co-Authors: Enliang Wang, Xu Shan, Shanshan Niu, Yaguo Tang, Qiguo Tian, Jing Yang, Maomao Gong, Xiangjun ChenAbstract:Electron Momentum spectroscopy is a unique tool for imaging orbital-specific Electron density of molecule in Momentum space. However, the molecular geometry information is usually veiled due to the single-centered character of Momentum space wavefunction of molecular orbital (MO). Here we demonstrate the retrieval of interatomic distances from the multicenter interference effect revealed in the ratios of Electron Momentum profiles between two MOs with symmetric and anti-symmetric characters. A very sensitive dependence of the oscillation period on interatomic distance is observed, which is used to determine F-F distance in CF4 and O-O distance in CO2 with sub-Angstrom precision. Thus, using one spectrometer, and in one measurement, the Electron density distributions of MOs and the molecular geometry information can be obtained simultaneously. Our approach provides a new robust tool for imaging molecules with high precision and has potential to apply to ultrafast imaging of molecular dynamics if combined with ultrashort Electron pulses in the future.
N Watanabe - One of the best experts on this subject based on the ideXlab platform.
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Electron Momentum spectroscopy study on the valence Electronic structure of methyl formate.
The Journal of chemical physics, 2019Co-Authors: N Watanabe, Kimihiro Sato, Masahiko TakahashiAbstract:We report an Electron Momentum spectroscopy study on methyl formate. A symmetric noncoplanar (e, 2e) experiment has been performed at an incident Electron energy of 1.2 keV and Electron Momentum profiles of the valence orbitals have been obtained. On the basis of the result, assignments of the 10a'-1 and 1a″-1 bands have been made to resolve a contradiction between photoElectron spectroscopy and Penning ionization Electron spectroscopy studies. Comparisons between experiment and theory reveal that the influence of the molecular vibration has to be taken into account for a proper understanding of the Electron Momentum profiles. Contributions of individual vibrational normal modes have also been investigated in detail by means of the harmonic analytical quantum mechanical approach.
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Influence of molecular vibrations on the valence Electron Momentum distributions of adamantane
The Journal of Chemical Physics, 2017Co-Authors: Filippo Morini, Michael S. Deleuze, N Watanabe, Masataka Kojima, Masahiko TakahashiAbstract:We report an Electron Momentum spectroscopy study of vibrational effects on the Electron Momentum distributions of the outer valence orbitals of adamantane (C10H16). The symmetric noncoplanar (e, 2e) experiment has been carried out at an incident Electron energy of 1.2 keV. Furthermore, theoretical calculations of the Electron Momentum distributions with vibrational effects being involved have been performed using the harmonic analytical quantum mechanical and Born-Oppenheimer molecular dynamics approaches. In spite of the complex nature of the vibrational structure of this large molecule, both approaches provide overall quantitative insights into the results of the experiment. Comparisons between experiment and theory have shown that ground state nuclear dynamics appreciably affects the Momentum profiles of the 7t2, {2t1 + 3e}, and {5t2 + 5a1} orbitals. It has been demonstrated that changes in the Momentum profiles are mainly due to the vibrational motions associated with the CH bonds.
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EMS study of vibrational effects on Electron Momentum distributions of C2H4 and CH2F2
Journal of Physics: Conference Series, 2015Co-Authors: N Watanabe, Masakazu Yamazaki, Masahiko TakahashiAbstract:We report an Electron Momentum spectroscopy study of vibrational effects on the Electron Momentum distributions for the outer valence orbitals of C2H4 and CH2F2. The symmetric noncoplanar (e,2e) experiment has been conducted at impact energy of 1.2 keV. Furthermore, a theoretical method of calculating Electron Momentum distributions has been developed with vibrational effects being involved. The experimental and theoretical results for these molecules strongly suggest that vibrational effects on Electron Momentum distributions tend to be appreciable for non-total symmetry molecular orbitals delocalized over some equivalent CH-bond sites.
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Vibrational effects on valence Electron Momentum distributions of ethylene
Journal of Chemical Physics, 2014Co-Authors: N Watanabe, Masakazu Yamazaki, Masahiko TakahashiAbstract:We report an Electron Momentum spectroscopy study of vibrational effects on the Electron Momentum distributions for the outer valence orbitals of difluoromethane (CH2F2). The symmetric noncoplanar (e,2e) experiment has been performed at an incident Electron energy of 1.2 keV. Furthermore, a theoretical calculation of the Electron Momentum distributions of the CH2F2 molecule has been carried out with vibrational effects being involved. It is shown from comparisons between experiment and theory that it is essential to take into account influences of the CH2 asymmetric stretching and CH2 rocking vibrational modes for a proper understanding of the Electron Momentum distribution of the 2b1 orbital having the CH-bonding character. The results of CH2F2and additional theoretical calculations for (CH3)2O and H2CO molecules strongly suggest that vibrational effects on Electron Momentum distributions tend to be appreciable for non-total symmetry molecular orbitals delocalized over some equivalent CH-bond sites.
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Vibrational effects on valence Electron Momentum distributions of ethylene.
The Journal of chemical physics, 2012Co-Authors: N Watanabe, Masakazu Yamazaki, Masahiko TakahashiAbstract:We report an Electron Momentum spectroscopy study of vibrational effects on the Electron Momentum distributions for the outer valence orbitals of ethylene (C(2)H(4)). The symmetric noncoplanar (e,2e) experiment has been conducted at an impact energy of 1.2 keV. Furthermore, a theoretical method of calculating Electron Momentum distributions for polyatomic molecules has been developed with vibrational effects being involved. It is shown from comparisons between experiment and theory that taking into account effects of the CH(2) asymmetric stretching and CH(2) rocking vibrational modes of C(2)H(4) is essential for a proper understanding of the Electron Momentum distribution of the 1b(3g) molecular orbital.