[P-CG23] Origin and evolution of materials in space

[PCG23-P04] Laboratory Detection of New Absorption Bands of Interstellar-Molecule Candidate Thiophenoxy Radical

Haruka Sato¹, Mayu Negishi¹, *Mitsunori Araki¹, Takahiro Oyama¹, Koichi Tsukiyama¹ (1.Department of Chemistry, Faculty of Science Division I, Tokyo University of Science)

Keywords:Interstellar molecule, Diffuse Interstellar Bands, DIBs, Cavity Ring Down, thiophenoxy radical

Diffuse Interstellar Bands (DIBs) are absorption bands detected in diffuse clouds by optical observations. Although ~600 DIBs have been found so far, only the five bands were assigned to the fullerene cation and the other bands are not identified yet. Recently, benzonitrile (C₆H₅CN) was detected in interstellar space by radio as the first aromatic compound [1]. Thus, thiophenoxy radical (C₆H₅S) is received much attentions as a candidate of DIBs, because sulfur is a dominant element of interstellar molecules. For this molecule, the origin band, which is a pure electronic transition without effects of molecular vibrations, was observed as the strongest band of the ²A₂–X²B₁ electronic transition [2,3]. However, our previous measurement of phenoxy radical (C₆H₅O) showed the strong vibronic bands with effects of molecular vibrations [4]. Thus, strong vibronic bands of C₆H₅S are expected because of similarity of the two molecules. We investigated the vibronic bands in the 473 – 519 nm region by Cavity Ring Down spectroscopy and detected them. The strongest vibronic band at 4850 Å was assigned to the 6a₀² + 6b₀¹ transition. This band is thought to be a candidate of DIB.

[1] McGuire et al. Science, 359, 202 (2018). [2] Shibuya et al., J. Chem. Phys. 121, 237 (1988). [3] Araki et al., Astronomical J. 148, 87 (2014). [4] Araki et al., Astronomical J. 150, 113 (2015).