The rotational spectrum up to 1 THz and the molecular structure of thiomethylium, HCS +

The rotational spectra of HCS+, DCS+, and HC34S+ have been investigated using a newly constructed ion cell in selected regions between 0.46 and 0.94 THz. 23 transitions covering the quantum numbers 10 ⩽ J″ ⩽ 25 have been used in a combined fit together with previous data to improve the rotational and quartic centrifigal distortion constants B0 and D0, respectively. High J transitions have been measured specifically to obtain an estimate of the sextic distortion constant H0. Vibration rotation coupling constants αi were obtained from coupled cluster calculations. They were used to determine a mixed experimental/ab initio equilibrium structure re.