Ab initio potential energy surface,infrared spectra,and dynamics of the ion-molecule complexes between Br~- and H_2,D_2,and HD

摘要

A three-dimensional potential energy surface (PES) for the Br~--H_2 complex is computed using the ab initio CCSD(T) method and an extended basis set.The PES has two equivalent minima at the linear geometries (equilibrium interfragment distance R_e = 3.34 A and interaction energy D_e=670 cm~(-1)) separated by the barrier at the T-shaped configuration (interfragment distance R_e=4.03 A and barrier height of 610 cm~(-1)).Ab initio points are fitted to a flexible analytical form and used in the variational rovibrational energy level calculations.Simulated infrared spectra of the Br~--H_2 and Br~--D_2 complexes in the monomer stretching excitation region are in good agreement with the measured ones.Nonstatistical intensity ratios of the complexes of para- and ortho-monomers are qualitatively explained by monomer ligand exchange reactions.Predissociation of the complexes containing vibrationally excited monomers is analyzed and shown to proceed through the near-resonant vibration-to-rotation energy transfer.For complexes involving Br~- and the HD monomer,two energetically low-lying states are predicted,corresponding predominately to the Br~--DH and Br~--HD isomeric forms.The results demonstrate the close similarity of the bromide containing complexes to their analogs containing the chloride anion.