Theoretical study of the visible photodissociation spectrum of Ar3

The six A′ potential energy surfaces were computed by a DIM-like method involving a valence-bond quasidiabatic basis. Transition dipole moments were also determined using a similar method. The 4D dynamics of this system (restricted to a molecular plane fixed in space) was obtained with the HWD method (hemiquantal dynamics with the whole DIM basis) and the visible photoabsorption spectrum was determined with the help of a 1D full quantum mechanical program applied to each normal mode. The photoabsorption spectrum of Ar₃⁺ was calculated in the range 440–710 nm. It corresponds to photodissociation since the excited Ar₃⁺ ions almost all dissociate into the Ar⁺ +Ar+Ar channel by a rapid explosion of the cluster, and only very few into Ar₂⁺ +Ar. It is dominated by a transition to the second excited state along with a symmetric stretching motion. We found a prominent 80 nm wide peak centered at 530 nm, with a maximum cross section of 4.2 × 10⁻¹⁶cm². The Ar₂⁺ formation results from a transition to the first excited state under low-energy laser excitation and is controlled by non-adiabatic transitions.