Exploring the excited states of the AsCl radical: A theoretical contribution

Abstract

A manifold of electronic states for the AsCl radical are accurately characterized at the MRCI+Q level of theory. The potential energy curves (PECs) of 34 Λ-S states, correlated with three dissociation channels, have been constructed, and the spectroscopic constants of the bound Λ-S are determined. The calculated spectroscopic results well reproduce the measurement. A characteristic feature for AsCl is that the open-shell π2 configuration can give rise to the lowest three strongly bound states X3Σ−, a1Δ, and b1Σ+. The spin-orbit (SO) coupling is included using the state interacting method. The calculated SO matrix element indicates that strongly bound a1Δ and b1Σ+ states can be predissociated by A3Π. The SO coupling effect leads to total 74 Ω states. And the calculated energy splitting of X3Σ− amounts to 125 cm−1, in good agreement with the experimental value of 140 ± 8 cm−1. Both a1Δ and b1Σ+ have no SO coupling splitting, and their spectroscopic constants almost keep unchanged. Nevertheless, their dissociation energies De are strongly decreased due to the avoided crossing. Transition mechanism of several important transitions for AsCl has been clearly expounded. Particularly, the nonzero transition dipole moments (TDMs) of transitions a1Δ-X3Σ− and b1Σ+-X3Σ− are borrowed from spin-allowed Λ-S transitions. Ultimately, the radiative lifetimes of a1Δ and b1Σ+ are determined to be 27.1 ms and 1.1 ms, respectively.