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 a 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.