An ab initio study of multiphoton bound-bound electronic transitions of H2S

Multiphoton absorption properties of H 2 S, transition probability coefficients and polarisation ratios are studied at ab initio level according to quantum electrodynamical methods, by employing RPA vertical excitation energies and transition moments and taking the random molecular orientation into account. The spectral observables associated with absorption of two, three and four photons with identical frequency and polarisation for the low-lying singlet excited states are reported. The concerted absorption of two or three photons with various polarisations from two laser beams is investigated as a function of the photon energies. The magnitude and direction of the electrochromic effects induced by a static external electric field on the molecular two-photon spectral properties are also analysed.