The 27th International Conference on Atomic Physics

Valence-shell electronic excitations of CH$_{3}$I studied by fast electron scattering

Not scheduled

1h 30m

Abstract of recent or ongoing work (by remote / virtual participant) Structure and properties of atoms, ions, and molecules Abstracts by remote participants

Description

CH$_{3}$I is an important trace species in the Earth’s atmosphere, which is mainly produced by biogenic processes. Meanwhile, CH$_{3}$I can release iodine atom, whose ozone depleting efficiency is about two to three orders of magnitude larger than that of chlorine. However, CH$_{3}$I is considered to be relatively environmentally friendly because of its short lifetime in the troposphere due to solar photolysis. Therefore, benchmark physical quantities including the oscillator strengths and cross sections of the valence-shell excitations of CH$_{3}$I are vital for monitoring the concentrations of CH$_{3}$I as well as for understanding its photophysics.
Since Price observed the first VUV photoabsorption spectrum of CH$_{3}$I, extensive experimental and theoretical researches on the electronic structure of CH$_{3}$I were reported and well summarized by Locht et al. recently[1]. However, there are few reports on the optical oscillator strengths (OOSs) of the valence-shell excitations of CH$_{3}$I, which have been summarized by Olney et al. [2]. Unfortunately, the generalized oscillator strengths (GOSs) and integral cross sections (ICSs) of the valence-shell excitations of CH$_{3}$I have not been reported until now, to the best of our knowledge.
In this context, the GOSs of the valence-shell excitations of CH$_{3}$I have been determined by an angle-resolved electron energy loss spectrometer at an incident electron energy of 1.5 keV and an energy resolution of 80 meV. The corresponding OOSs have been obtained by extrapolating the GOSs to the zero limit of squared momentum transfer $\mathrm{K}^2$→0, which are in good agreement with the previous data. Moreover, the ICSs of the valence-shell excitations of CH$_{3}$I from the threshold to 5000 eV have also been obtained by means of the BE-scaling method[3,4]. The GOSs of the first two Rydberg states and some of their vibrational states are shown in Fig. 1 and Fig. 2. It is obvious that all GOSs show a similar trend, i.e., decreasing with the $\mathrm{K}^2$ in the small $\mathrm{K}^2$ region, which is the typical behavior of the dipole allowed transitions.
In general, we measure the GOSs of the valence-shell excitations of CH$_{3}$I and obtain the corresponding extrapolated OOSs by a completely different experimental method, thus providing an independent cross-check for previous results. Furthermore, the ICSs of the valence-shell excitations of CH$_{3}$I were systematically obtained, which enrich the fundamental spectroscopic data of CH$_{3}$I and have important application value in photochemical models of atmospheric physics.

[1] T.N. Olney et al. Chemical Physics 232, 211–237 (1998).
[2] R. Locht et al. Chemical Physics 365, 109–128 (2009).
[3] Kim, Y. K. Physical Review A, 64(3), 032713 (2001).
[4] Kim, Y. K. The Journal of chemical physics, 126(6), 064305 (2007).