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

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 angstrom, around 0.02 angstrom 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)). (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4754131