Electron momentum spectroscopy of dimethyl ether taking account of nuclear dynamics in the electronic ground state

Abstract

The influence of nuclear dynamics in the electronic ground state on the (e,2e) momentum profiles of dimethyl ether has been analyzed using the harmonic analytical quantum mechanical and Born-Oppenheimer molecular dynamics approaches. In spite of fundamental methodological differences, results obtained with both approaches consistently demonstrate that molecular vibrations in the electronic ground state have a most appreciable influence on the momentum profiles associated to the 2b1, 6a1, 4b2, and 1a2 orbitals. Taking this influence into account considerably improves the agreement between theoretical and newly obtained experimental momentum profiles, with improved statistical accuracy. Both approaches point out in particular the most appreciable role which is played by a few specific molecular vibrations of A1, B1, and B2 symmetries, which correspond to C-H stretching and H-C-H bending modes. In line with the Herzberg-Teller principle, the influence of these molecular vibrations on the computed momentum profiles can be unraveled from considerations on the symmetry characteristics of orbitals and their energy spacing.

Influence of molecular vibrations on the valence electron momentum distributions of adamantane

“…Comparisons between experiment and theory has shown that taking into account vibrational effects lead to appreciable enhancement of the low p component of the 7t 2 , {2t 1 +3e} and {5t 2 +5a 1 } momentum profiles and considerably improve the agreement with experiment. Further analysis based on the HAQM approach has revealed the significant role of vibrational modes associated with the CH bonds, in line with previous results on molecules with several CH bonds 30,[34][35][36]38 in their contribution to the change of momentum profiles.…”

“…For the {2t 1 +3e} orbitals, the CH wag mode also gives a noticeable contribution to the associated momentum profile at the low p region. The results indicate that taking into account contributions from the normal modes associated with CH bonds is essential for understanding the observed increase in intensity of the 7t 2 and {2t 1 +3e} momentum profiles at small p, being consistent with previous results on ethylene, 30 CH 2 F 2 , 34 furan, 35 dimethyl ether, 36 and oxetane 38 in their contributions to the change of momentum profiles.…”

“…[25][26][27][28] Because of its unique ability to image individual electron orbitals in momentum space, EMS can provide a powerful means to investigate how molecular orbital patterns are affected by the vibrational motions of molecules. Indeed, recent EMS studies on various polyatomic molecules [29][30][31][32][33][34][35][36][37][38] have shown that electron momentum profiles may considerably be affected by molecular vibrations, and that EMS experiments in conjunction with recently developed theoretical approaches are capable of disentangling the interplay between the electronic and nuclear dynamics. 30,31,[34][35][36][37][38] It is therefore of interest to apply the EMS technique to the study of the nuclear dynamics effects for diamondoids.…”

Temperature-Dependent Electron Momentum Spectroscopy on the Molecular Orbitals of Dimethyl Ether

“…It was calculated according to the method employed in our previous study. 19 Briefly, a normal mode analysis was carried out using DFT along with the B3LYP functional and aug-cc-pVTZ basis. The KS orbitals were subsequently computed at several nuclear geometries distorted from the equilibrium along each normal coordinate and converted to ρ α (p,Q)'s by means of the HEMS program, assuming constant spectroscopic factors for all orbitals considered.…”

“…This molecule has already been the subject of detailed EMS studies at room temperature, 16−19 and appreciable vibrational effects have been identified so far in the electron momentum profiles. 19 It is natural to expect that a larger influence of the nuclear dynamics to the molecular orbitals arises from vibrational excitation, which can easily be induced by heating the sample as dimethyl ether has low-frequency vibrational modes. EMS measurements have thus been performed at a high temperature, 980 K, using a radiative heating system developed in our laboratory.…”