Photoabsorption, photoionization, and neutral dissociation cross sections of dimethyl ether and ethyl methyl ether in the extreme-ultraviolet range

Abstract

The absolute photoionization and neutral dissociation cross sections of dimethyl ether (CH3OCH3) and ethyl methyl ether (CH3CH2OCH3) in the 52–92 nm range have been obtained by measuring the absolute photoabsorption cross sections and photoionization quantum yields using a multistage ionization chamber and synchrotron radiation. A large deviation in the photoionization quantum yield of both molecules from unity, namely a noticeable enhancement of the neutral fragmentation cross sections, has shown that superexcited states exist densely in this wavelength range. Fluorescence excitation spectra of neutral dissociation fragments produced in the 35–100 nm photon impact on both molecules have also been measured by observing ultraviolet and vacuum ultraviolet emissions. A general appearance of the neutral dissociation cross sections correlates with the fluorescence excitation spectra from H(n=2), CH(A 2Δ), and CH3O(Ã). The superexcited states of dimethyl ether observed are shown to be purely repulsive states or bound states for which the lowest energy level achieved from the Franck–Condon region is higher than the dissociation limit. Dissociation of ionic satellites have also been observed in the fluorescence excitation spectra of both molecules.