The structure, spectroscopy, and excited state predissociation dynamics of GeH2

Abstract

The spectroscopy and excited state dynamics of à 1B 1 germylene (GeH2) have been investigated experimentally and theoretically. Jet-cooled laser-induced fluorescence spectra of GeH 2 were obtained by subjecting germane (GeH4) to an electric discharge at the exit of a pulsed nozzle. The band origins of ten vibronic transitions were determined, giving values for the upper state fundamentals of ν1 =783.0 cm-1 and ν2 = 1798.4 cm-1. Sufficient numbers of 000 band rovibronic transitions were observed to give the ground and excited state structures as r″=1.591(7) Å, θ″=91.2(8)° and r′ = 1.553(12) Å, θ′ = 123.4(19)°. Fluorescence lifetime measurements show that the 00,0 rotational levels decay radiatively; higher J rotational states in the 00 vibronic level decay much faster, due to a heterogeneous predissociation in the excited state. High quality ab initio studies are consistent with a model in which the lower vibronic levels of the A state predissociate through the ã 3B1 state to produce Ge(3P)+H2( 1Σg+). The transition state for this process has been located and the barrier to dissociation is 15.2 kcal/mol above the à 1B1 state, so that tunneling through the barrier must occur. Above 4000 cm-1 of vibrational energy in the A state, a breaking off of fluorescence is observed as a second predissociation channel involving GeH2(à 1B1) →Ge(1D)+H2(1Σg+) becomes accessible. This process is also found to have a barrier, in contrast to previous theoretical studies of SiH2, where the analogous dissociation was predicted to be barrierless. © 1995 American Institute of Physics.