Ab initio excitation spectrum of the weak He⋯BF interaction

Abstract

The adiabatic interaction energy IE of the ground He^{1}S…BFX}^{1}Σ^{+} and excited He^{1}S…BFa}^{3}Π electronic states of the van der Waals vdW system {He}…{BF} are studied in the present contribution in the framework of the supermolecule approach at the RHF-CCSDT level of theory. Calculations predict a global minimum and a shallow local minimum separated by a saddle point for the ground state; the most stable configuration occurs at βe=180°, equilibrium distance Re=6.63 a_{\rm o} and equilibrium dissociation energy De=21.87 cm^{-1}. The calculated IE for the excited ^{3}{A'} state reveals two local minima and a global minimum separated by saddle points; the most stable configuration occurs at βe=121°, R_{e}=6.15a_{o} and De=28.27 cm^{-1}. The resulting IE of the excited ^{3}{A''} state reveals two minima separated by a saddle point; the most stable configuration occurs at βe =76°, R_{e}=6.02 a_{o} and De=38.47 cm^{-1}. The corresponding vertical electronic excitation energies and shifts in the fluorescent spectrum with respect to the isolated {BF} molecule are calculated as a guideline for future theoretical and experimental work.