Electronic state dependence in the dissociation of core-ionized methane

Methane and deuteromethane molecules were core ionized using synchrotron radiation, and the ionic fragments from the molecular dissociation were detected in coincidence with the Auger electrons. The electron-ion coincidence spectra are analysed in terms of partial ion yields and ion kinetic energy distributions, both as functions of electron kinetic energy. The dependence of the fragmentation patterns on the electronic character of the Auger final states as well as on the excess energy available for dissociating the molecule is studied. The analysis reveals marked differences in the dissociation of the 2a^-2₁ and 2a^-1₁1t^-1 ₂ states, interpreted as an 'excess-energy-dependent' concerted dissociation process for the 2a^-2₁ state and an 'electronic-state-dependent' sequential process for the 2a^-1 ₁1t^-1₂ state.