A LABORATORY AND THEORETICAL STUDY OF PROTONATED CARBON DISULFIDE, HSCS$^+$

Abstract

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 $K_a=0$ ladder of the normal isotopic species, HS$^{13}$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$_2^+$ potential energy surface; HCSS$^+$, an isomer with $C_{2v}$ 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.