PNNL

Abstract

Photoexcited molecular trajectories on the potential energy surfaces prior to thermalization are intimately connected to the photochemical reaction outcome. The excited state trajectories of a diplatinum complex featuring photo-activated metal-metal ??-bond formation and associated Pt-Pt stretching motions were detected in real time using femtosecond wide angle X-ray solution scattering. The observed motions correspond well with coherent vibrational wavepacket motions detected by femtosecond optical transient ab-sorption. Two key coordinates for intersystem crossing have been identified, the Pt-Pt bond distance and the orientation of the ligands coordinated with the platinum centers, along which the excited state trajectories can be projected onto the calculated potential energy surfaces of the excited states. This investigation has gleaned novel insight into electronic transitions occurring on the time scales of vibrational motions measured in real time, revealing ultrafast nonadiabatic or non-equilibrium processes along excited state trajectories involving multiple excited state potential energy surfaces.