Two photon bound-bound electronic transition calculations in molecules

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Abstract
Calculations of the transition probability for the two photon excitation from the ground to some of the first excited electronic states in both NH3 and HF are presented. The transitions are taken to be vertical and a random molecular orientation is assumed. The transition moments needed to evaluate the transition amplitudes are computed by using the random phase approximation (RPA), that directly supplies the initial state-intermediate states one-electron transition density matrices and the excitation energies, while the intermediate states-final state one-electron transition density matrices are obtained from the RPA results through an equation of motion method (EMM) technique. The effect of mixing of the excitation channels is investigated. For each chosen final state enough data are supplied to give a thorough account of the dependence of the transition probability upon the polarization of the radiation and the experimental geometrical set-up. The calculations are performed using both the length and the velocity forms of the perturbing operator.