Ultraviolet photodissociation of Mg+-NO complex: Ion imaging of a reaction branching in the excited states

Ultraviolet photodissociation processes of gas phase Mg+-NO complex were studied by photofragment ion imaging experiments and theoretical calculations for excited electronic states. At 355 nm excitation, both Mg+ and NO+ photofragment ions were observed with positive anisotropy parameters, and theoretical calculations revealed that the two dissociation channels originate from an electronic transition from a bonding orbital consisting of Mg+ 3s and NO pi* orbitals to an antibonding counterpart. For the NO+ channel, the photofragment image exhibited a high anisotropy (beta = 1.53 +/- 0.07), and a relatively large fraction (similar to 40%) of the available energy was partitioned into translational energy. These observations are rationalized by proposing a rapid dissociation process on a repulsive potential energy surface correlated to the Mg(S-1) + NO+((1)Sigma) dissociation limit. In contrast, for the Mg+ channel, the angular distribution was more isotropic (beta = 0.48 +/- 0.03) and only similar to 25% of the available energy was released into translational energy. The differences in the recoil distribution for these competing channels imply a reaction branching on the excited state surface. On the theoretical potential surface of the excited state, we found a deep well facilitating an isomerization from bent geometry in the Franck-Condon region to linear and/or T-shaped isomer. As a result, the Mg + fragment was formed via the structural change followed by further relaxation to lower electronic states correlated to the Mg (+)(S-2) + NO((2)Pi) exit channel. Published under an exclusive license by AIP Publishing.

Automated summary

The ultraviolet photodissociation processes of gas phase Mg+-NO complex were studied using both experiments and theoretical calculations. The experimental results showed the formation of Mg+ and NO+ ions, and the theoretical calculations explained the origin of these dissociation channels. The NO+ channel exhibited high anisotropy and a larger fraction of translational energy, while the Mg+ channel showed more isotropic angular distribution and less translational energy release.