Laboratory Optical Spectroscopy of Thiophenoxy Radical and Its Profile Simulation as a Diffuse Interstellar Band Based on Rotational Distribution by Radiation and Collisions

TL;DR

This study investigates the optical spectrum of the thiophenoxy radical as a potential diffuse interstellar band (DIB) candidate, combining experimental spectroscopy, theoretical calculations, and rotational profile simulations to assess its viability.

Contribution

It provides the first experimental spectrum of the thiophenoxy radical and models its rotational profile considering radiation and collisions, offering insights into its role as a DIB candidate.

Findings

The observed spectrum did not match the simulated profile.

An upper limit for the radical's column density in diffuse clouds was estimated.

Rotational distribution effects are crucial for modeling DIB profiles.

Abstract

The gas-phase optical absorption spectrum of a thiophenoxy radical (C6H5S), a diffuse interstellar band (DIB) candidate molecule, was observed in the discharge of thiophenol using a cavity ringdown spectrometer. The ground-state rotational constants of the thiophenoxy radical were theoretically calculated, and the excited-state rotational constants were determined from the observed rotational profile. The rotational profile of a near prolate molecule having a C2v symmetry was simulated on the basis of a rotational distribution model by radiation and collisions. Although the simulated profile did not agree with the observed DIBs, the upper limit of the column density for the thiophenoxy radical in the diffuse clouds toward HD 204827 was evaluated. The profile simulation indicates that rotational distribution by radiation and collisions is important to reproduce a rotational profile for a DIB candidate and that the near prolate C2v molecule is a possible candidate for DIB with a band width variation dependent on line-of-sight.