The ground state of germylidene (H2C=Ge)

Abstract

Single vibronic level emission spectra have been obtained by pumping individual vibronic bands in the B̃1B2–X̃1A1 electronic transitions of jet-cooled H2CGe and D2CGe. Analysis of the spectra gave for the first time the frequencies of the following ground state fundamentals: for H2CGe, ν2=1238 cm−1, ν3=782 cm−1, ν4=673 cm−1, ν6=351 cm−1, and for D2CGe, ν1=2089 cm−1, ν2=1000 cm−1, ν3=694 cm−1, ν4=520 cm−1, and ν6=282 cm−1. The vibrational data have been combined with our previously determined molecular structures to obtain approximate harmonic force fields for the ground and excited states. Franck–Condon simulations of the emission spectra in the harmonic approximation show reasonable agreement with experiment, except for unexpected activity in the out-of-plane bending mode. This is attributed to a very anharmonic out-of-plane bending potential in the S2 excited state. Germylidene also has a very low ground state CH2 rocking frequency (ν6) which is along the normal coordinate leading to isomerization to the less stable trans-bent germyne isomer, H–C≡Ge–H.