2-PHOTON TRANSITION-PROBABILITY CALCULATIONS - ELECTRONIC-TRANSITIONS IN METHANE

Results obtained in the calculation of the transition probabilities for the two-photon excitation from the ground to some low-lying excited electronic states in methane, under the hypothesis of vertical transitions of randomly oriented molecules, are accounted for. The one-electron transition density matrices of interest in the computation are obtained by a non-standard application of the random phase approximation (RPA). A comparison between the results obtained both by allowing and by suppressing the coupling of the excitation channels is presented. For each final state the transition rate for a particular choice of the photon polarisation parameters is displayed. This supplies all information needed to compute the transition rates at each photon energy for every possible combination of geometrical arrangement and polarisation choice. Both length and velocity forms of the perturbing operator are employed in the calculations.