High-level theoretical rovibrational spectroscopy of HCS+ isotopologues

•Highly accurate near-equilibrium potential energy surface for HCS+ from composite method.•Effective spectroscopic parameters from variational calculations of rovibrational states.•Analysis of the experimentally observed Fermi resonance.•Prediction of spectroscopic parameters and band intensities for isotopologues.

In this work the rovibrational spectrum of the HCS+ molecular cation is revisited through high-level electronic structure and variational rovibrational calculations. A local potential energy function is built from explicitly correlated coupled-cluster results, incorporating corrections for core-valence, scalar relativistic and higher-order excitation effects. The computed spectroscopic parameters, based on variational calculations with Watson's isomorphic Hamiltonian for linear molecules lead to a nearly perfect agreement with experimentally reported values (Rosenbaum et al., 1989). Furthermore, the documented Fermi resonance within the (0,00,1)/(0,20,0) and (1,00,1)/(1,20,0) pairs of states is clarified. Based on a newly developed electric dipole moment function transition dipole moments of fundamental transitions are predicted for the most important isotopologues.

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