Vibronic Coupling in Formamide Radical Cation: A Full Dimensional Quantum Mechanical Study.

Formamide is the simplest amide, consists of one amide bond, and is an active precursor in prebiotic chemistry. Extensive ab initio calculations have been carried out for the first four electronic and a vibronic coupling Hamiltonian is constructed through the standard vibronic coupling approach, and nuclear dynamics is studied by quantum dynamical methods. Symmetry selection rules are employed, and a 4 ×× 4 vibronic Hamiltonian is developed in a diabatic electronic basis. The electronic Hamiltonian elements are expanded using Taylor expansion in terms of normal displacement coordinates (Q iᵢ ) of vibrational modes. Both time-independent and time-dependent quantum mechanical methods are utilized in performing nuclear dynamics calculations. The computed and assigned vibronic spectrum is compared with the available experimental data. Time-dependent internal conversion population dynamics is studied to examine the effect of various nonadiabatic couplings in nuclear dynamics.