THE EXCITED ELECTRONIC STATES OF H2CSI

We have studied the excited electronic states of silylidene(1-silaviny lidene), H2CSi, by nb initio quantum-mechanical methods to determine t heir equilibrium geometries, relative energies, and harmonic vibration al frequencies. Besides the ground (1)A(1) state, we have also studied the (1)A(2) and (3)A(2) states, obtained by exciting an electron from the pi orbital of silylidene to a p(y) lone pair orbital, and the B-1 (2) and B-3(2) states obtained by exciting an electron from an a(1) sy mmetry silicon lone pair orbital to the p(y) orbital. We have also inv estigated the lowest-lying cation states. Our predictions of the geome tries of the (1)A(1) ground state and second excited singlet state, B- 1(2),,,, in good agreement with the experimental results of Harper, Wa ddell, and Clouthier [J. Chem. Phys. 107, 8829 (1997)]. Our predicted excitation energies and excited state vibrational frequencies also agr ee well with experimental values. The geometry of the (B) over tilde B -1(2) State differs markedly, and unexpectedly, from that of the (X) o ver tilde(1)A(1) and (B) over tilde(3)B(2) states. We explain this as resulting from the large electron repulsion between the unpaired elect rons in the (B) over tilde state, which essentially reside on the same atom. (C) 1997 American Institute of Physics.