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

TL;DR

This study uses microwave spectral taxonomy to identify and analyze vibrationally excited states of C2S, C3S, and C4S, providing precise data to aid astronomical searches and demonstrating the method's effectiveness as a bridge to millimeter-wave spectroscopy.

Contribution

It introduces microwave spectral taxonomy for complex mixture analysis and extends vibrational state identification of sulfur-carbon chains to millimeter-wave frequencies.

Findings

Detected over 85 variants including new isotopic and vibrational states.

Identified vibrationally excited states in archival millimeter-wave data.

Provided accurate catalogs for astronomical detection of C2S, C3S, and C4S.

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.