Automated Exploration of Photolytic Channels of HCOOH: Conformational Memory via Excited-State Roaming

作者：Maeda Satoshi^*; Taketsugu Tetsuya; Morokuma Keiji

来源：Journal of Physical Chemistry Letters, 2012, 3(14): 1900-1907.

DOI：10.1021/jz300728q

To elucidate the photodissociation mechanism of HCOOH, we systematically explored reaction pathways starting from the first excited singlet state (S-1) by using automated reaction path search methods. All critical points, that is, minima, transition states, minimum energy conical intersections, and minima on seam of crossing, for the S-0, T-1, and S-1 potential energy surfaces (PESs) obtained in the present search were optimized at the CASPT2 level. The structure list obtained by the search explained all experimentally reported photolytic channels. A new mechanism for the previously suggested but unexplained conformational memory in the 193 nm photolysis is proposed, which involves two steps: partial dissociation and succeeding roaming of one of H atoms on the S-1 PES, followed by intramolecular recombination on the S-0 PES after radiationless transition through a conical intersection at a partially dissociated geometry. This is partially similar to the excited-state roaming recently discovered for the NO3 radical.

• 出版日期2012-7-19