Ab initio excitation spectrum of the weak He⋯BF interaction

Abstract

The adiabatic interaction energy (IE) of the ground $\mathrm{He}\mathrm{(}{}^1\mathrm{S}\mathrm{)}\cdots \mathrm{BF}\mathrm{(}{\mathit{X}}^1{\mathrm{\Sigma }}^{+}\mathrm{)}$ and excited $\mathrm{He}\mathrm{(}{}^1\mathrm{S}\mathrm{)}\cdots \mathrm{BF}\mathrm{(}{\mathit{a}}^3\mathrm{\Pi }\mathrm{)}$ electronic states of the van der Waals (vdW) system He $\cdots$ BF are studied in the present contribution in the framework of the supermolecule approach at the RHF-CCSD(T) 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_o and equilibrium dissociation energy De=21.87 cm⁻¹. The calculated IE for the excited ${}^3{\mathit{A}}^{\prime }$ state reveals two local minima and a global minimum separated by saddle points; the most stable configuration occurs at βe=121°, R_e=6.15 a_o and De=28.27 cm⁻¹. The resulting IE of the excited ${}^3{\mathit{A}}^{″}$ 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.