Rotationally resolved infrared spectrum of the Br−−D2 anion complex

Abstract

The midinfrared spectrum of the Br−79−D2 anion complex is measured in the D2 stretch region by monitoring the production of Br− photofragments in a tandem mass spectrometer. The rotationally resolved spectrum comprises two overlapping Σ−Σ subbands, red-shifted by ≈85 cm−1 from the free D2 vibrational frequency. These subbands are assigned to absorptions by Br−−D2 complexes containing para and ortho forms of the D2 molecule. The Br−−D2 complex is deduced to possess a linear equilibrium geometry, although the zero-point bending excursion is expected to be substantial. The rotational constants are consistent with vibrationally averaged intermolecular separations between the Br− anion and D2 center of mass of 3.414(4) Å for Br−−D2(p) and 3.413(1) Å for Br−−D2(o). The intermolecular bond contracts by 0.076 Å following vibrational excitation of the D2 diatomic molecule. Effective one-dimensional radial potential energy curves are developed through Rydberg–Klein–Rees inversion of the spectroscopic data and consideration of the long-range electrostatic and induction interaction between the D2 molecule and a point charge. On the basis of these potential energy curves the binding energies of Br−−D2(p) and Br−−D2(o) are estimated as 364 and 418 cm−1, respectively.