Product angular distributions in the ultraviolet photodissociation of N2O

The angular distribution of products from the ultraviolet photodissociation of nitrous oxide yielding O(D-1) and N-2(X-1 Sigma(+)(g)) was investigated using classical trajectory calculations. The calculations modeled absorption only to the 2(1)A' electronic state but used surface-hopping techniques to model nonadiabatic transitions to the ground electronic state late in the dissociation. Observed values of the anisotropy parameter beta, which decrease as the product N-2 rotational quantum number j increases, could be well reproduced. The relatively low observed beta values arise principally from nonaxial recoil due to the very strong bending forces present in the excited state. In the main part of the product rotational distribution near 203 nm, an unusual dynamical effect produces the decrease in beta with increasing j; nonaxial recoil effects remain approximately constant while higher j product molecules arise from parent molecules that had their transition dipole moments aligned more closely along the molecular axis. In both low and high j tails of the rotational distribution, the variations in beta with j are caused by changes in the extent of nonaxial recoil. In the high-j tail, additional torque present on the ground state potential energy surface following nonadiabatic transitions causes both the additional rotational excitation and the lower beta values. (C) 2012 American Institute of Physics. [doi:10.1063/1.3679171]