Knowledge Bank

The rotational spectrum of protonated carbon disulfide, HSCS$+$, has been detected in the centimeter-wave band in a molecular beam by Fourier transform microwave spectroscopy. Rotational and centrifugal distortion constants have been determined from transitions in the $Ka=0$ ladder of the normal isotopic species, HS$\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}$CS$+$, and DSCS$+$. The present assignment agrees well with high-level coupled cluster calculations of the HSCS$+$ structure, which, like earlier work, predict this isomer to be the ground state on the HCS$\mathrm{2+}$ potential energy surface; HCSS$+$, an isomer with $C2v$ symmetry, is predicted to lie more than 20~kcal/mol higher in energy. Other properties of HSCS$+$ including its dipole moment, vibrational frequencies, and infrared intensities have also been calculated at the CCSD(T)/cc-pwCVQZ level of theory. Because carbon disulfide possesses a fairly large proton affinity, and because this nonpolar molecule may plausible exist in astronomical sources, HSCS$+$ is a good candidate for detection with radio telescopes in the sub-millimeter band where the stronger $b$-type transitions of this protonated cation are predicted to lie.