Germyne, H–C≡Ge–H, and the excited states of 1-germavinylidene, H2C=Ge

Abstract

We have used ab initio quantum-mechanical methods to study the electronic states of germavinylidene, H2C=Ge, and the isomerization of ground-state singlet germavinylidene to the less stable trans-bent germyne isomer, H–C≡Ge–H. The electronic states of germavinylidene that we have studied are the ground A11 state, the A21 and A23 states, involving a π to py transition, and the B21 and B23 states obtained from the ground state by an n to py transition. We have also investigated the ground state of the germavinylidene anion, and the two lowest-lying cation states. Our predicted B̃ 1B2–X̃ 1A1 excitation energy agrees well with the recent experimental value. The geometries of the B21 and B23 states of germavinylidene might be expected to be similar, but they differ by 0.1 Å in the Ge–C bond length and 12° in the H–C–H bond angle. This results from the large electron repulsion between the unpaired electrons in the B21 state, which essentially reside on the same atom. The anomalously low value of the CH2 rocking frequency in germavinylidene is rationalized as a second-order Jahn–Teller effect. Finally, the trans-bent germyne isomer requires 7 kcal mol−1 to isomerize to the germavinylidene isomer, which is 43 kcal mol−1 more stable than germyne.