THE STRUCTURE, SPECTROSCOPY, AND EXCITED-STATE PREDISSOCIATION DYNAMICS OF GEH2

The spectroscopy and excited state dynamics of ($) over tilde A B-1(1) germylene (GeH2) have been investigated experimentally and theoretica lly. Jet-cooled laser-induced fluorescence spectra of GeH2 were obtain ed by subjecting germane (GeH4) to an electric discharge at the exit o f a pulsed nozzle. The band origins of ten vibronic transitions were d etermined, giving values for the upper state fundamentals of v(1)=783. 0 cm(-1) and v(2)=1798.4 cm(-1). Sufficient numbers of 0(0)(0) band ro vibronic transitions were observed to give the ground and excited stat e structures as r ''=1.591(7) Angstrom, theta ''=91.2(8)degrees and r' =1.553(12) Angstrom, theta'=123.4(19)degrees. Fluorescence lifetime me asurements show that the 0(0,0), rotational levels decay radiatively; higher J rotational states in the 0(0) vibronic level decay much faste r, due to a heterogeneous predissociation in the excited state. High q uality ab initio studies are consistent with a model in which the lowe r vibronic levels of the ($) over tilde A state predissociate through the ($) over tilde a B-3(1) state to produce Ge(P-3)+H-2((1) Sigma(g)( +)). The transition state for this process has been located and the ba rrier to dissociation is 15.2 kcal/mol above the ($) over tilde A B-1( 1) state, so that tunneling through the barrier must occur. Above 4000 cm(-1) of vibrational energy in the ($) over tilde A state, a breakin g off of fluorescence is observed as a second predissociation channel involving GeH2(($) over tilde A B-1(1))-->Ge(D-1)+H-2((1) Sigma(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. (C) 1995 American Instit ute of Physics.