Study of pair and many-body interactions in rare-gas halide atom clusters using negative ion zero electron kinetic energy (ZEKE) and threshold photodetachemnt spectroscopy

The diatomic halogen atom-rare gas diatomic complexes KrBr− , XeBr−, and KrCl− are studied in this work by zero electron kinetic energy (ZEKE) spectroscopy in order to characterize the weak intermolecular diatomic potentials of these species. Also, the ZEKE and threshold photodetachment spectra of the polyatomic clusters Ar_nBr− (n = 2–9) and Ar_nI − (n = 2–19) are studied to obtain information about the non-additive effects on the interactions among the atoms. This work is part of an ongoing effort to characterize the pair and many-body potentials of the complete series of rare gas halide clusters. In these studies we obtain information about both the anionic and neutral clusters.; In the spectra of the diatomic complex we observe well-resolved vibrational structure which is used in conjunction with scattering results from the literature to construct accurate intermolecular potentials. We also obtain accurate electron affinities for these species.; From the spectra of the polyatomic species we obtain accurate electron affinities and electronic state term values. We observe some partially resolved vibrational structure for Ar_nBr− (n = 2–3) and Ar_nI− (n = 2–3). The global minimum energy structures of the clusters are found using a molecular-dynamics based simulated annealing algorithm. The electron affinities calculated using these structures and the pair potentials obtained from previous ZEKE studies of the ArBr− and ArI− complexes are found to be inconsistent with the experimentally observed electron affinities, indicating the importance of non-additive effects in these clusters. Various non-additive interactions are considered, and the most important are found to be non-additive induction effects and the effect arising from the interaction of the halide charge with the multipole moments due to the distortion of the rare-gas electron clouds. For the neutral clusters Ar_nBr (n = 2–3) and Ar_nI (n = 2–7) we also observe many-body effects in the electronic structure due to the presence of the open-shell halogen atom. These effects are successfully modeled using a simple degenerate perturbation theory treatment of the open shell-closed shell interaction.