(pi pi*/pi sigma*) Conical Intersection Seam Experimentally Observed in the S-D Bond Dissociation Reaction of Thiophenol-d(1)

Abstract

Surface crossing of bound (S-1, pi pi*) and continuum (S-2, pi sigma*) states has been observed in the ultrafast S-D bond dissociation reaction of thiophenol-d(1). It is manifested by an unanticipated variation of fragment angular distribution as a function of the excitation energy. The anisotropy parameter (beta) of +0.25 at the S-1 origin decreases to -0.60 at similar to 600 cm(-1) above the S-1 zero-point level, giving a broad peak in beta with a bandwidth of similar to 200 cm(-1). The peak in beta is ascribed to the in-plane S-D bending mode excitation by which the nuclear configuration in the proximity of the S-1/S-2 conical intersection seam is directly accessed, showing a mixed character of parallel (S-1-S-0) and perpendicular (S-2-S-0 transition dipole moments at the same time. As a result, the dynamic aspect of the conical intersection is experimentally revealed here through direct access to the nuclear configuration on the multidimensional conical intersection seam.