Electronic vertical excitation spectrum of the weak H⋯BF complex

The counterpoise-corrected adiabatic interaction energy (IE) of the ground H(2S)⋯BF(X1Σ+) and excited H(2S)⋯BF(a3Π) electronic states of the H⋯BF van der Waals (vdW) complex is firstly studied in the present contribution in the framework of the supermolecule approach at the CCSD(T) and the partially spin-restricted RCCSD(T) levels of theory, respectively, using the aug-cc-pVQZ augmented basis set complemented with a set of 33211 standard midbond functions. Calculations predict a single minimum for the X2A′ ground state; the most stable configuration occurring at β = 74°, distance R = 6.60 ao and equilibrium dissociation energy De = 46.84 cm−1. The calculated IE for the excited 4A′ state reveals two local minima and a global minimum separated by saddle points, where the most stable configuration occurs at β = 122°, R = 6.44 ao with De = 41.09 cm−1. The resulting IE of the excited 4A″ state reveals a single minimum. The most stable configuration occurs at β = 79°, R = 6.43 ao with De = 52.71 cm−1. A basis set extrapolation procedure was employed to estimate the complete basis set limit of the bonding parameters. The corresponding vertical excitation-energy shifts in the fluorescent spectrum with respect to the isolated BF molecule are calculated as a guideline for future theoretical and experimental work.