Franck-Condon simulation of the photoelectron spectrum of AsCl(2) and the photodetachment spectrum of AsCl?2- employing UCCSD(T)-F12a potential energy functions: IE and EA of AsCl(2)

The currently most reliable theoretical estimates of the adiabatic ionization energies (AIE0) from the X?2B1 state of AsCl2 to the X?1A1 and ã3B1 states of AsCl, and the electron affinity (EA0) of AsCl2, including ?ZPE corrections, are calculated as 8.687(11), 11.320(23), and 1.845(12) eV, respectively (estimated uncertainties based on basis-set effects at the RCCSD(T) level). State-of-the-art ab initio calculations, which include RCCSD(T), CASSCF/MRCI, and explicitly correlated RHF/UCCSD(T)-F12x (x = a or b) calculations with basis sets of up to quintuple-zeta quality, have been carried out on the X?2B1 state of AsCl2, the X?1A1, ã3B1, and Ã1B1 states of AsCl, and the X?1A1 state of AsCl. Relativistic, core correlation and complete basis-set (CBS) effects have been considered. In addition, computed UCCSD(T)-F12a potential energy functions of relevant electronic states of AsCl2, AsCl, and AsCl were used to calculate Franck–Condon factors, which were then used to simulate the valence photoelectron spectrum of AsCl2 and the photodetachment spectrum of AsCl, both yet to be recorded. Lastly, we have also computed the AIE and EA values for NCl2, PCl2, and AsCl2 at the G4 level and for SbCl2 at the RCCSD(T)/CBS level. The trends in the AIE and EA values of the group V pnictogen dichlorides, PnCl2, where Pn = N, P, As, and Sb, were examined. The AIE and EA of PCl2 were found to be smaller than those of AsCl2, contrary to the order expected from the IE values of P and As