The photochemical reaction paths in aqueous PtBr(6)(2-) and OsBr(6)(2-) have been studied by femtosecond broad-band pump probe spectroscopy supported by CASPT2 and DFT/TDDFT calculations. These paths lead to the separation of negative charges and propagate through distortions of nascent, penta-coordinated metal fragments caused by Jahn-Teller C(4v) and D(3h) conical intersections (CIs), respectively. Within 150 fs following 420 nm excitation of PtBr(6)(2-), the molecule undergoes internal conversion and intersystem crossing into the dissociative lowest triplet excited (3)T(1g) state, loses a ligand, and relaxes via the C(4v) CI to the nearly trigonal bipyramid (3)PtBr(5)(-) product in the triplet state. Direct 530 nm excitation of PtBr(6)(2-) to (3)T(1g) yields. the same product. Oscillations observed in the bending and umbrella a(1) modes of (3)PtBr(5)(-) arise from impulsive excitation of, respectively, one of the reaction coordinate modes, which is parallel to the gradient difference vector of the C(4v) CI, and the "spectator" mode that preserves the electronic degeneracy.
Zheldakov, Igor L.; Ryazantsev, Mikhail N.; and Tarnovsky, Alexander N., "Wavepacket Motion Via A Conical Intersection In The Photochemistry Of Aqueous Transition-metal Dianions" (2011). Chemistry Faculty Publications. 57.
Journal Of Physical Chemistry Letters