GERMYNE, H-C-GE-H, AND THE EXCITED-STATES OF 1-GERMAVINYLIDENE, H2C=GE

We have used ab initio quantum-mechanical methods to study the electro nic states of germavinylidene, H2C=Ge, and the isomerization of ground -state singlet germavinylidene to the less stable trans-bent germyne i somer, H-C-=Ge-H. The electronic states of germavinylidene that we hav e studied are the ground (1)A(1) state, the (1)A(2) and (3)A(2) states , involving a pi to p(y) transition, and the B-1(2) and B-3(2) states obtained from the ground state by an n to p(y) transition. We have als o investigated the ground state of the germavinylidene anion, and the two lowest-lying cation states. Our predicted (B) over tilde B-1(2)-(X ) over tilde (1)A(1) excitation energy agrees well with the recent exp erimental value. The geometries of the B-1(2) and B-3(2) states of ger mavinylidene might he expected to be similar, but they by 0.1 Angstrom in the Ge-C bond length and 12 degrees in the H-C-H bond angle. This results from the large electron repulsion between the unpaired electro ns in the B-1(2) 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 tr ans-bent germyne isomer requires 7 kcal mol(-1) to isomerize to the ge rmavinylidene isomer, which is 43 kcal mol(-1) more stable than germyn e. (C) 1998 American Institute of Physics. [S0021-9606(98)02213-2].