The production and characterization by resonance enhanced multiphoton ionization of H2(v=10–14) from photodissociation of H2S

Abstract

The excitation of H2S at 66 000 cm−1 by two-photon absorption is shown to produce significant quantities of H2 molecules in very high vibrational, but low rotational levels. The vibrationally excited H2 has been identified by a 2+1+1 resonance enhanced multiphoton ionization (REMPI) process in whch the Ẽ,F̃ state is excited as an intermediate state. The major contribution of this double well state comes from the outer F̃ well because of the large H2 bond distance in the nascent H2(v) photoproduct. Excitation of the Ẽ,F̃ state by a 291 nm photon dissociates the molecule to the H+H*(n=3) products, and the excited atom is then ionized by a fourth photon. The analysis of the photoelectron spectra (PES) demonstrates that the intermediate H2S* molecule preferentially dissociates to vibrationally excited H2 molecules rather than ionizing by the absorption of an additional photon. It appears likely that the photodissociation of H2S is a practical method for producing highly vibrationally excited, but rotationally cool, H2 molecules for further dynamical studies.