Non-adiabatic effects on resonance-enhanced Raman scattering in H2

Resonance-enhanced Raman scattering (RERS) from the ground X1Σg+(νg = 0, Jg) state of H2 via the excited intermediate C1Πu(ν = 0/1/2/3, Ji) state coupled non-adiabatically with the B1Σu+(νiB = 8/10/12/14, Ji) state was studied theoretically, applying second-order perturbation theory. The excitation and Raman spectra for the pure rotational, fundamental and higher overtones are presented. Effects of non-adiabatic coupling on the excitation profiles, scattered intensities and depolarization ratios were investigated. The intensities of excitation spectra and Raman lines for O-, Q- and S-branches were calculated using thermal Boltzmann factors for vibrational–rotational distribution at room temperature (300 K). The RERS cross-sections with adiabatic and non-adiabatic corrections are reported together with Born–Oppenheimer (BO) results where available, for comparison. The calculated RERS cross-sections including non-adiabatic effects were found to vary significantly from adiabatic or BO results.