Interpreting vibrationally resolved spectra of molecular dications (doublypositively charged molecules): HCl2+

Vibrationally resolved spectra of HCl2+ appear to show five vibrational lev els for the X(3)Sigma(-) ground electronic state, whereas calculations of v ibrational levels supported by ab initio potential energy curves have been able to locate only three vibrational levels below the barrier: this discre pancy is resolved by considering vibrational states that the potential func tion supports in the continuum above the barrier maximum. A low resolution spectrum produced from first principles is compared with a spectrum obtaine d with threshold photoelectrons in coincidence (TPEsCO) spectroscopy, with agreement sufficient to suggest that carl must be taken in the inversion of vibrational spectroscopic data for molecular dications to avoid generating potential functions that are too strongly bound.