Theoretical Study of Valence Shell Excitation by Electron Impact in CCl₄

Abstract

This paper reports a theoretical study of valence shell excitation in CCl 4 by high-energy electron impact. Generalized oscillator strengths are calculated for the molecule at the equation-of-motion coupled-cluster singles and doubles level. To elucidate the influence of nuclear dynamics on electron excitation cross-sections, the effects of molecular vibration are included in the calculation. Based on a comparison with recent experimental data, several reassignments of spectral features are made, and it is found that excitations from the Cl 3p nonbonding orbitals to σ* antibonding orbitals, 7a 1 and 8t 2 , play dominant roles below the excitation energy of ∼9 eV. Furthermore, the calculations reveal that distortion of the molecular structure due to the asymmetric stretching vibration significantly affects the valence excitations at small momentum transfers, where contributions from dipole transitions are dominant. It indicates that vibrational effects have a considerable influence on Cl formation in the photolysis of CCl 4 .

Plasma-relevant fast electron impact study of difluoromethane

“…More exactly, Palmer et al [15] yielded higher oscillator strengths than the experimental data while Zhan et al [18] predicted much lower values. The ignored vibronic effects might be the reason for the difference between the observations and calculations [49][50][51].…”

Vibronic effect study of 1A2 state of H2O and D2O

“…It has been demonstrated that such a theoretical calculation procedure can successfully elucidate the momentum transfer dependence behaviors of GOSs for many molecules. [2,4,[6][7][8][9] In this work, the GOSs of the 1 A 2 ←− X1 A 1 transitions of H 2 O and D 2 O were calculated by using Gaussian16 software, to elucidate the influence of the vibronic effect on this transition character. The vibrational normal coordinates and vibrational frequencies of H 2 O and D 2 O were calculated using 053401-2 the basis set of aug-cc-pVTZ [34,35] at the treatment level of the second-order Mφ ller-Plesset perturbation theory (MP2).…”

“…Although electron collisional excitation cross sections for the low electronic states of H 2 O have been extensively studied both theoretically [17][18][19][20] and experimentally, [17,[21][22][23][24][25][26] the influence of the vibronic effect on them has not been considered while it has great influence on other molecules. [1][2][3][4][5][6][7][8][9] This paper focuses on the vibronic effect and isotopic effects of the dipole-forbidden transition 1 A 2 of H 2 O and D 2 O, and according to the previous investigations, [1][2][3][4][5][6][7][8][9] the vibronic effect on this transition should be prominent. The 1 A 2 states of H 2 O and D 2 O were noticed in the electron energy loss spectra at the impact electron energies of 100 eV-200 eV, [25] 300 eV-500 eV, [27] and 1500 eV.…”

“…Vibronic effect, induced by the molecular vibration which distorts the molecular symmetry and couples the electronic and nuclear motions, has great influence on the molecular dynamic parameters, such as the generalized oscillator strengths (GOSs), optical oscillator strengths (OOSs), differential cross sections (DCSs), and integral cross sections (ICSs). [1][2][3][4][5][6][7][8][9] Furthermore, the vibronic effect can change the transition behaviors such as converting the dipole-forbidden transitions into the dipole-allowed ones, enhancing the intensities of the GOS in the small squared momentum transfer region, etc. Therefore, the influence of vibronic effect on the GOSs of the valence-shell excitations of atoms and molecules has attracted the interests of both experimentalists and theorists, and recently the vibronic effects for molecular CF 4 , [1,2] NH 3 , [3,4] N 2 O, [5,6] CCl 4 , [7,8] CH 3 Cl, [9] CF 3 Cl, [9] etc., have been studied extensively.…”

“…[1][2][3][4][5][6][7][8][9] Furthermore, the vibronic effect can change the transition behaviors such as converting the dipole-forbidden transitions into the dipole-allowed ones, enhancing the intensities of the GOS in the small squared momentum transfer region, etc. Therefore, the influence of vibronic effect on the GOSs of the valence-shell excitations of atoms and molecules has attracted the interests of both experimentalists and theorists, and recently the vibronic effects for molecular CF 4 , [1,2] NH 3 , [3,4] N 2 O, [5,6] CCl 4 , [7,8] CH 3 Cl, [9] CF 3 Cl, [9] etc., have been studied extensively. The present paper focuses on the vibronic effect on the GOSs of the valence-shell excitations of H 2 O and D 2 O, and it is clearly elucidated that the isotopic substitution has an apparent influence on the vibronic effect.…”