Effect of the excitation energy on the (HI)2 nonadiabatic photodissociation dynamics.

The effect of the excitation energy on the nonadiabatic photodissociation dynamics of (HI)2 is explored in this work. A wave packet model is applied that simulates the photodissociation process starting from the I*-HI complex left behind after dissociation of the first HI moiety within (HI)2. The probability and product fragment state distributions of the different photodissociation pathways are analyzed in a wide range of excitation energies of the I*-HI absorption spectrum. It is found that the probability of electronically nonadiabatic transitions increases substantially (by a factor larger than two) in the range of excitation energies analyzed. This increase is due to an enhancement of the intensity of the spin-rotation coupling responsible for the nonadiabatic transitions with increasing excitation energy. A remarkably high fraction of bound, highly excited I2 photoproducts, slowly decreasing as the excitation energy increases, is also found over the range of energies studied. The I2 product state distributions show manifestations of rotational interference effects and also of rotational cooling in the case of the I2 state distributions produced upon nonadiabatic transitions. Such effects become more pronounced with increasing energy. Experimental implications of these findings are discussed.