PHOTOABSORPTION, PHOTOIONIZATION, AND NEUTRAL DISSOCIATION CROSS-SECTIONS OF DIMETHYL ETHER AND ETHYL METHYL-ETHER IN THE EXTREME-ULTRAVIOLET RANGE

The absolute photoionization and neutral dissociation cross sections o f dimethyl ether (CH3OCH3) and ethyl methyl ether (CH3CH2OCH3) in the 52-92 nm range have been obtained by measuring the absolute photoabsor ption cross sections and photoionization quantum yields using a multis tage ionization chamber and synchrotron radiation. A large deviation i n the photionization quantum yield of both molecules from unity, namel y 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 fragmen ts produced in the 35-100 nm photon impact on both molecules have also been measured by observing ultraviolet and vacuum ultraviolet emissio ns. A general appearance of the neutral dissociation cross section cor relates with the fluorescence excitation spectra from H (n = 2), CH (A (2)DELTA), and CH3O(A approximately). The superexcited states of dime thyl ether observed are shown to be purely repulsive states or bound s tates for which the lowest energy level achieved from the Franck-Condo n region is higher than the dissociation limit. Dissociation of ionic satellites have also been observed in the fluorescence excitation spec tra of both molecules.