The infrared spectrum of HCl2+ and its isotopomers

We report ab initio calculations of potential energy and dipole functions for the lowest four electronic states of the doubly charged molecule (molecular dication) HCl2+. Spectroscopic constants are evaluated for the three states which support quasibound vibration-rotation levels, as are the lifetimes of these levels due to both spin-orbit mediated electronic predissociation and tunnelling. The prevalent model of bonding in doubly charged molecules is that of Coulomb repulsion plus a bonding attraction; for HCl2+ this model is inappropriate because the charge is not centred equally on the two nuclei except at large bond lengths. We compare calculations with experimental data and discuss the feasibility of observing infrared spectra of HCl2+ isotopomers in a fast ion beam/laser beam spectrometer.