(ππ*/πσ*) Conical Intersection Seam Experimentally Observed in the S–D Bond Dissociation Reaction of Thiophenol-d1

Surface crossing of bound (S 1, ππ*) and continuum (S 2, πσ*) 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 (β) of +0.25 at the S 1 origin decreases to −0.60 at ∼600 cm –1 above the S 1 zero-point level, giving a broad peak in β with a bandwidth of ∼200 cm –1 . The peak in β 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.