Generalized oscillator strengths of low-lying electronic excitations in acetylene

Abstract

This paper reports a theoretical study on electron-impact excitations of acetylene. Momentum-transfer-dependent generalized oscillator strengths (GOSs) or GOS profiles have been calculated using wavefunctions at the equation-of-motion coupled-cluster singles and doubles level. In the calculation the influence of molecular vibration has been taken into account. The computed results are in overall agreement with experimental GOS profiles reported in the literature. Our theoretical analysis has revealed prominent roles of bending vibrations in the low-lying valence excitations induced by electron impact.

The Study of the Low-Lying Valence-Shell Excitations of Hydrogen Sulfide by Fast Electron Impact

“…It should be noticed that for I, its GOS has a much stronger maximum at about 0.5 a.u., which does not follow the typical behavior of a dipole-allowed transition. A similar phenomenon has also been observed for acetylene, which may be attributed to the vibration effect …”

Theoretical Study of Valence Shell Excitation by Electron Impact in CCl4

“…may be ascribed, at least partly, to the failure of the Born approximation, which has often been observed at large momentum transfer. , On the other hand, it is unlikely that the disagreement at K 2 < ∼1 a.u. can be fully attributed to contributions from the second and higher Born terms since theoretical calculations based on the Born approximation have shown good agreement with experimental data for various molecules at small K 2 . − Other possible sources of the discrepancy are discussed later.…”

“…The GOS profiles of transitions to low-lying excited singlet-states have been calculated for the molecule at the equation-of-motion coupled-cluster singles and doubles (EOM-CCSD) level and compared with the recent experimental data. The EOM-CCSD method is known to yield accurate excitation energies and has further been shown to give good predictions of GOS profiles. − Here, it should be noted that at momentum transfer close to zero, electronic excitations by electron impact are dominated by dipole transitions, − and owing to the high symmetry of CCl 4 , only a limited number of excited states are accessible from the ground state if the molecular structure is kept rigid at the equilibrium geometry. However, the structural distortion induced by molecular vibrations may lead to considerable contributions from dipole forbidden transitions to GOSs even at small momentum transfer; thus, such vibrational effects are investigated.…”

Excited states of aurocarbons: CASPT2 and CCSD(T) calculations of C2Au2 and C2Au4

“…Valence and Rydberg excited states of acetylene, the parent molecule of diauroacetylene, have been a subject of numerous detailed theoretical and experimental investigations, see, for example, Ventura et al [32], Wetmore and Schaefer [51], Malsch et al [52], Bowman and Miller [53], Dressler and Allan [54], Tsuji et al [55], Hammond et al [56], Demoulin and Jungen [57], Perić et al [58], Patterson et al [59], and Watanabe and Takahashi [60]…”

“…Numerous theoretical investigations on valence, Rydberg and valence/Rydberg mixed excited states of ethylene, including [26–70] offer deep insight into the understanding of (not easy) basic features of experimental electronic spectra of ethylene. In Table 6, we present results of our CASPT2 calculations in comparison with selected theoretical and experimental data from literature.…”