Single-hole one-electron superexcited states and doubly excited states of methane in the vacuum ultraviolet range as studied by dispersed fluorescence spectroscopy

The absolute values of the fluorescence cross sections for CH(A, B → X) and H( n = 4– 7 → n ' = 2) in the photoexcitation of methane have been obtained as a function of incident photon energy in the range 12.65–41 eV, in which five superexcited states have been found and discussed quantitatively in detail. The lower two of them are single-hole one-electron superexcited states and the higher three around 25, 29 and 35 eV are doubly excited states, which have been investigated in detail for the first time in this experiment. It is remarkable that the oscillator strengths for the emission of the fluorescences originating from the doubly excited states are as large as or even larger than those from the single-hole one-electron superexcited (2a 1 ) −1 ( n pt 2 ) 1 T 2 states, which seems not to be amenable to the independent electron model.