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 Title: LABORATORY OPTICAL SPECTROSCOPY OF THE PHENOXY RADICAL AS A DIFFUSE INTERSTELLAR BANDS CANDIDATE Author(s): Araki, Mitsunori Contributor(s): Tsukiyama, Koichi; MATSUSHITA, Yuki Subject(s): Astronomy Abstract: Diffuse Interstellar Bands (DIBs) are optical absorption lines observed in diffuse clouds in interstellar space. They still remain the longest standing unsolved problem in spectroscopy and astrochemistry, although several hundreds of DIBs have been already detected. Aromatic radicals in a gas phase are potential DIB candidate molecules. The electronic transitions of aromatic radicals result in optical absorption. Last year we reported the gas-phase optical absorption spectrum of the $^{2}A_{2} leftarrow X ^{2}B_{1}$ transition of the thiophenoxy radical C$_{6}$H$_{5}$S using a cavity ringdown spectrometer.footnote{MF14}$^,$footnote{Araki, Niwayama, and Tsukiyama, $Astronomical Journal$, 148, 87 (5pp), 2014} As the next step, we observed the $B^{2}A_{2} leftarrow X^{2}B_{1}$ transition of the phenoxy radical C$_{6}$H$_{5}$O in the discharge of anisole. The four broad and asymmetric peaks making a progression of 500 cm$^{-1}$ were detected in the 5700--6450 AA region. The progression was assigned to the 6a mode, and the broad and asymmetric peak profiles were accounted for by the sequences of the 10b mode. Each vibrational component has a broad structure of 23 AA, which can be explained by lifetime broadening. Based on the assignment of the progression and the sequences, the vibronic components from $v$ = 0 in the $X ^{2}B_{1}$ ground state can be extracted from the broad and asymmetric peak profiles to compare the laboratory bands with DIBs. Although the components did not agree with the reported DIBs, the upper limit of the column density for the phenoxy radical in the diffuse clouds toward HD 204827 was evaluated to be 4 $times$ 10$^{14}$ cm$^{-2}$. Therefore the most fundamental aromatic radicals, the thiophenoxy and phenoxy radicals, could not explain DIBs observed at present. Issue Date: 25-Jun-15 Publisher: International Symposium on Molecular Spectroscopy Citation Info: ACS Genre: CONFERENCE PAPER/PRESENTATION Type: Text Language: English URI: http://hdl.handle.net/2142/79239 Date Available in IDEALS: 2016-01-05
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