Properties of the B+-H2 and B+-D2 complexes: A theoretical and spectroscopic study

Abstract

The rotationally resolved infrared spectrum of the B(+)-D(2) ion-neutral complex is recorded in the D-D stretch vibration region (2805-2875 cm(-1)) by detecting B(+) photofragments. Analysis of the spectrum confirms a T-shaped equilibrium geometry for the B(+)-D(2) complex with a vibrationally averaged intermolecular bond length of 2.247 Å, around 0.02 Å shorter than for the previously characterised B(+)-H(2) complex [V. Dryza, B. L. J. Poad, and E. J. Bieske, J. Am. Chem. Soc. 130, 12986 (2008)]. The D-D stretch band centre occurs at 2839.76 ± 0.10 cm(-1), representing a -153.8 cm(-1) shift from the Q(1)(0) transition of the free D(2) molecule. A new three dimensional ab initio potential energy surface for the B(+)+H(2) interaction is calculated using the coupled cluster RCCSD(T) method and is used in variational calculations for the rovibrational energies of B(+)-H(2) and B(+)-D(2). The calculations predict dissociation energies of 1254 cm(-1) for B(+)-H(2) with respect to the B(+)+H(2) (j = 0) limit, and 1313 cm(-1) for B(+)-D(2) with respect to the B(+)+D(2) (j = 0) limit. The theoretical approach reproduces the rotational and centrifugal constants of the B(+)-H(2) and B(+)-D(2) complexes to within 3%, and the magnitude of the contraction of the intermolecular bond accompanying excitation of the H(2) or D(2) sub-unit, but underestimates the H-H and D-D vibrational band shifts by 7%-8%. Combining the theoretical and experimental results allows a new, more accurate estimation for the B(+)-H(2) band origin (3939.64 ± 0.10 cm(-1)).