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

The spectroscopy and excited state dynamics of à 1B1 germylene (GeH2) have been investigated experimentally and theoretically. Jet-cooled laser-induced fluorescence spectra of GeH2 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 à state predissociate through the ã 3B1 state to produce Ge(3P)+H2(1Σ+g). 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 à state, a breaking off of fluorescence is observed as a second predissociation channel involving GeH2(à 1B1)→Ge(1D)+H2(1Σ+g) 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.