HEAVY-ATOM TUNNELING IN CYCLOBUTADIENE - ABINITIO CALCULATION OF THE INTENSITIES OF A(G) RAMAN LINES

GVB/[5s3p1d/3s1p] calculations were performed on the polarizability surface alpha(R1, R2, R3) of cyclobutadiene, The three a(g) coordinates refer to automerization (R1), symmetric CC stretch (R2), and symmetric CCH bend (R3). This surface was used together with the previously obtained variational vibrational wave functions for the calculation of Raman Intensities. The calculation predicts comparable intensities for the two split components of the automerization Raman line in an isolated molecule and disagrees with observations on matrix-isolated cyclobutadiene. The disagreement is attributed to the asymmetry of the double-well potential imposed by the effect of the Ar matrix.