Vibrational Satellites of C${}_2$S, C${}_3$S, and C${}_4$S: Microwave Spectral Taxonomy as a Stepping Stone to the Millimeter-Wave Band

Abstract

We present a microwave spectral taxonomy study of several hydrocarbon/CS${}_2$ discharge mixtures in which more than 60 distinct chemical species, their more abundant isotopic species, and/or their vibrationally excited states were detected using chirped-pulse and cavity Fourier-transform microwave spectroscopies. Taken together, in excess of 85 unique variants were detected, including several new isotopic species and more than 25 new vibrationally excited states of C${}_2$S, C${}_3$S, and C${}_4$S, which have been assigned on the basis of published vibration-rotation interaction constants for C${}_3$S, or newly calculated ones for C${}_2$S and C${}_4$S. On the basis of these precise, low-frequency measurements, several vibrationally exited states of C${}_2$S and C${}_3$S were subsequently identified in archival millimeter-wave data in the 253--280 GHz frequency range, ultimately providing highly accurate catalogs for astronomical searches. As part of this work, formation pathways of the two smaller carbon-sulfur chains were investigated using ${}^{13}$C isotopic spectroscopy, as was their vibrational excitation. The present study illustrates the utility of microwave spectral taxonomy as a tool for complex mixture analysis, and as a powerful and convenient `stepping stone' to higher frequency measurements in the millimeter and submillimeter bands.

Accepted in PCCP