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 Title: DETECTION OF NON-EMISSION VIBRONIC BANDS OF THIOPHENOXY RADICAL BY ABSORPTION SPECTROSCOPY Author(s): Araki, Mitsunori Contributor(s): Tsukiyama, Koichi ; Oyama, Takahiro ; Negishi, Mayu ; Sato, Haruka Subject(s): Astronomy Abstract: Diffuse Interstellar Bands (DIBs) are absorption bands detected in diffuse clouds by optical observations. Although $\sim$ 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 (\chem{C_6H_5CN}) was detected in interstellar space by radio as the first aromatic compound [1]. Thus, thiophenoxy radical (\chem{C_6H_5S}) is received much attentions as a candidate of DIBs, because sulfur is a dominant element of interstellar molecules. Fluorescence excitation spectra of the $^{2}A_{2}$--X $^{2}B_{1}$ electronic transition of \chem{C_6H_5S} showed the origin band as the strongest peak [2]. However, in our previous work, absorption spectra of phenoxy radical (\chem{C_6H_5O}) brought out the stronger vibronic bands than the origin band [3]. The fact suggests that intensities of higher vibronic bands of \chem{C_6H_5S} are lost by radiationless transitions in the fluorescence excitation spectra. Thus, stronger vibronic bands of \chem{C_6H_5S} 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 \AA was assigned to the 6a$_{0}^{2}$ + 6b$_{0}^{1}$ transition. This band may appear as DIB if sufficient amount of this radical exists in interstellar medium. [1] McGuire et al., Science, 359, 202 (2018). [2] Shibuya et al., J. Chem. Phys. 121, 237 (1988). [3] Araki et al., Astronomical J. 150, 113 (2015). Issue Date: 2019-06-21 Publisher: International Symposium on Molecular Spectroscopy Genre: Conference Paper / Presentation Type: Text Language: English URI: http://hdl.handle.net/2142/104314 DOI: 10.15278/isms.2019.FA01 Rights Information: Copyright 2019 Mitsunori Araki Date Available in IDEALS: 2019-07-152020-01-25
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