Resonance enhanced two-photon dissociation of H2 by the X→(E F+G K+I ) transition via intermediate B,C states

Abstract

The generalized resonance enhanced two-photon dissociation (RETPD) cross sections of H2 are calculated for linear parallel polarizations of the two photon fields. The reduced density operator formalism is used to study the wavelength and quantum number dependences for the transitions X 1Σ+g (vg=0, Jg=0–4) →vuv B 1Σ+u (C 1Πu) [vi=0,3, Ji=0(1)–3] →uv/visible [(EF+GK)1 Σ+g +I 1Πg, Ef, Jf]. By resonant absorption of the first photon an aligned population in the intermediate B(C) is created which is then dissociated by the second photon. The wavelength is so chosen that ionization from the resonant intermediate state is energetically forbidden. The contribution of the EF state to the total cross section is found to be negligible. The relative contribution of the GK and I states varies sharply with wavelength of the second photon and the resonant intermediate state. For both B and C states, dissociation through the I state is more prominent over a narrow range of wavelengths far from the dissociation threshold when the vibrational quantum number (vi) is large. For small vi the contribution of the I state is less. Due to the presence of a barrier above the dissociation threshold in the I state potential, narrow shape resonances occur. The cross sections at these shape resonances are a few orders of magnitude higher than the background. The detailed line shapes at these resonances have been presented for all the rotational quantum numbers considered for vi=0 and 3 of the B and C states.