Matrix-controlled photofragmentation of formamide: Dynamics simulation in argon by nonadiabatic QM/MM method

The short-time photodynamics (2 ps) of formamide embedded into an Ar matrix starting from the low-lying singlet excited S₁ (n₀π*) and S₂ (ππ*) states were explored using a nonadiabatic photodynamics QM/MM approach. The interaction between formamide and the Ar matrix is taken into account at the MM level by means of Lennard-Jones potentials. This is the first example of exploring photodissociation of formamide with full nonadiabatic dynamics in a matrix and it nicely illustrates importance of considering environmental effects on photodissociation behavior of the peptide bond. It is shown that embedding of the formamide molecule in the argon matrix has strong impact on the outcome of the process. This is illustrated by formation of the 1: 1 complex between ammonia and CO and prevention of full separation of the NH₂. and HCO. subunits in the NH₂. + HCO. radical pair. In addition, the argon matrix strongly influences the lifetime of the S₁ state, which increases by 211 fs relative to the gas phase.