Spin–orbit induced radiationless transitions in organometallics: Quantum simulation of the 1E→3A1 intersystem crossing process in HCo(CO)4

Abstract

A theoretical description of the ‘‘fast’’ (<50 ps) intersystem crossing processes occurring at critical geometries during the photodissociation of HCo(CO)4 is presented. The radiationless transitions are simulated by wave packet propagations along one‐dimensional reaction coordinate on the spin–orbit coupled potential energy surfaces. The propagation are performed separately, either along the Co–H bond or along the Co–COax bond. This original approach has enabled us to understand the mechanism of desactivation of the initially populated singlet excited state in this molecule which should be considered as a model for other organometallics. We propose the following mechanism: (i) in a very short time scale (<20 fs) 40% of the system dissociates towards the primary products H+Co(CO)4 (1 E), whereas the 1 E→3 A 1 intersystem crossing along the Co–H bond elongation occurs within 50 ps; (ii) the dissociation of an axial carbonyl ligand occurs in a larger time scale (200 fs) and only 2% of the system dissociates along the Co–COax elongation. The dominant process is the 1 E→3 A 1 intersystem crossing leading to HCo(CO)4(3 A 1); (iii) as soon as the lowest triplet state is populated, the system dissociates either to H+Co(CO)4 or to HCo(CO)3+COax on the 3 A 1potential energy surface; (iv) the intersystem crossing process may be described as a succession of elementary transitions occurring at critical geometries or crossing points between the singlet and the triplet potential energy surfaces; (v) the efficiency of the radiationless transition is governed by the overlap of the propagated wave packet with the critical region of the coupled potential energy surfaces.