Autoionization of acetylene studied by two-dimensional photoelectron spectroscopy

摘要

A two-dimensional (2D) photoelectron spectrum of acetylene is measured by using monochromatized synchrotron radiation. Vibrational excitation in the C-H stretching mode v_1 of C_2H_2~+(X ~2Π_u) is observed over a photon energy region from 13.0 to 14.1eV, which is due to autoionization of a valence state (3σ_g)~(-1)(3σ_u)~1. Constant ionic state spectra for the (v_1', v_2') = (3,0), (3,1), (4,0), and (4,1) vibrational levels of C_2H_2~+(X ~2Π_u) show two progressions originating from the v_1 motion in the (3σ_g)~(-1)(3σ_u)~1 state. It is likely that an autoionization lifetime of the valence state is comparable to vibrational periods of the v_1 and v_2 modes.