PSEUDOROTATIONAL INTERCONVERSION OF THE (2)A(1) AND B-2(2) STATES OF HCOO1

The lowest potential energy surface for the sigma formyloxyl radical ( sigma-HCOO) is investigated with an equation-of-motion coupled cluster technique and basis sets that contain up to 195 contracted Gaussian f unctions. The B-2(2) and (2)A(1) states of symmetric (C-2v) sigma-HCOO both lie on this surface and can be interconverted adiabatically by t ransporting the nuclei through nonsymmetric, but planar, intermediate geometries. In accord with previous high-level calculations, the poten tial energy surface that governs this pseudorotation process is predic ted to be extremely flat. While the (2)A(1) stale is found to be the h ighest point on the interconversion pathway when basis sets of modest size are used, this symmetric form is preferentially stabilized by bas is set augmentation. Calculations with very large basis sets suggest t hat both the (2)A(1) and B-2(2) C-2v structures are local minima on th e surface, separated by a barrier of about 500 cm(-1). These results a re in qualitative agreement with conclusions reached in a recent elect ron photodetachment experiment.