Quantum chemical rovibrational spectroscopic data for possible observation of thiocarbonic acid (H ₂ CS ₃ ) in interstellar environments

The second-lowest conformer of thiocarbonic acid (<i>cis</i>-<i>trans</i>-H₂CS₃) lies 0.64 kcal mol^-1 above the global minimum and possesses a 2.17 D dipole moment compared to the 0.75 D dipole moment of the <i>cis</i>-<i>cis</i> global minimum. While these properties are qualitatively similar to those of standard carbonic acid (H₂CO₃), the relative energy is lower, and the dipole moment of <i>cis</i>-<i>cis</i>-H₂CS₃ is higher than in <i>cis</i>-<i>cis</i>-H₂CO₃. As such, the quantum chemically computed spectroscopic constants and fundamental vibrational frequencies of these two conformers of thiocarbonic acid are provided in this work as well as those for the <i>trans</i>-<i>trans</i> conformer. Previous quantum chemical work has highlighted that the provided rotational constants should be within 3.5 MHz, if not 1.5 MHz, of experiment, and prior experimental work implies that this molecule can form on interstellar ices and be easily desorbed into the gas phase thereafter. Hence, these data will be able to assist in laboratory characterization or even potential interstellar searches for thiocarbonic acid.