Rotationally resolved infrared spectrum of the Br--D-2 anion complex

The midinfrared spectrum of the Br-79(-)-D-2 anion complex is measured in t he D-2 stretch region by monitoring the production of Br- photofragments in a tandem mass spectrometer. The rotationally resolved spectrum comprises t wo overlapping Sigma-Sigma subbands, red-shifted by approximate to 85 cm(-1 ) from the free D-2 vibrational frequency. These subbands are assigned to a bsorptions by Br--D-2 complexes containing para and ortho forms of the D-2 molecule. The Br--D-2 complex is deduced to possess a linear equilibrium ge ometry, although the zero-point bending excursion is expected to be substan tial. The rotational constants are consistent with vibrationally averaged i ntermolecular separations between the Br- anion and D-2 center of mass of 3 .414(4) Angstrom for Br--D-2(p) and 3.413(1) Angstrom for Br--D-2(o). The i ntermolecular bond contracts by 0.076 Angstrom following vibrational excita tion of the D-2 diatomic molecule. Effective one-dimensional radial potenti al energy curves are developed through Rydberg-Klein-Rees inversion of the spectroscopic data and consideration of the long-range electrostatic and in duction interaction between the D-2 molecule and a point charge. On the bas is of these potential energy curves the binding energies of Br--D-2(p) and Br--D-2(o) are estimated as 364 and 418 cm(-1), respectively. (C) 2001 Amer ican Institute of Physics.