Ultrafast dynamics of electronically excited diborane radical cation

Full-dimensional quantum mechanical study is carried out to investigate the vibronic structure and internal conversion dynamics of the energetically low-lying electronic excited states of (Formula presented.). A model diabatic electronic Hamiltonian, within the quadratic vibronic coupling approach comprising of five energetically low-lying electronic states, is developed, and the parameters of the Hamiltonian are estimated by performing extensive ab initio  electronic structure calculations using the equation-of-motion coupled-cluster singles and doubles method. The nuclear dynamics on the constructed diabatic electronic states is studied by employing both time-independent and time-dependent quantum mechanical methods. Theoretically calculated vibronic structure of the electronic states is found to be in excellent accord with the available experimental results. Extremely strong vibronic interactions among the electronic states result highly overlapping and diffuse vibronic bands and complicate the assignment of vibronic progression. Examination of non-radiative internal conversion dynamics revealed very short lifetime ((Formula presented.)60 fs) of the excited electronic states of (Formula presented.).