Tokyo Univ. Science Mitsunori Araki, Yuki Matsushita, Koichi Tsukiyama Laboratory Optical Spectroscopy of the Phenoxy Radical as a Diffuse Interstellar Bands Candidate Tokyo Univ. Science Mitsunori Araki, Yuki Matsushita, Koichi Tsukiyama 2018/11/15 2015/06/25

Diffuse Interstellar Bands Optical absorption lines by molecules in diffuse cloud Electronic Transition A or B ★ Absorption Diffuse Cloud X Near infrared ~ optical (line width: 0.5-50Å) First report: 1922 ~600 lines 2018/11/15

What are origins of DIBs ? Optical Transition 　 Ion and/or radical Large Molecule Not Identified yet Identification of DIBs 2018/11/15

Unidentified molecule How to identify DIBs ? Optical Electronic Transition Space Earth absorption Star Unidentified molecule DIB Lab Molecule Spectrometer Discharge etc. Spectra Identification fit 2018/11/15

Cavity Ring Down Spectrometer Hollow Cathode Discharge Pulsed dye laser, Dn = 0.2 cm-1, 10 Hz Discharge cell - Laser G Detector Absorption Electrodes 2018/11/15

Thiophenoxy Radical C6H5S Polyaromatic Hydrocarbon (PAH) 10% of interstellar molecules have a sulfur atom Benzene + sulfur atom Thiophenoxy Radical C6H5S Radical: Optical Electronic Transition B 2A2 ‹- X 2B1 2018/11/15 Wavelength /Å

HD204827 HD204827 The ８th Magnitude Star 380 DIBs ★ Observer Galactic Plane Celestial North Pole HD204827 The ８th Magnitude Star 380 DIBs Hobbs et al. 2008 ★ Observer 2018/11/15 HD204827

Araki et al., 2014, Astronomical J., 148, 87 Comparison with DIBs HD204827 No fit Upper limit of column density: 2×1013 cm-2 Wavelength /Å This meeting in 2014 2018/11/15 Araki et al., 2014, Astronomical J., 148, 87

Phenoxy Radical C6H5O Polyaromatic Hydrocarbon (PAH) 30% of interstellar molecules have oxygen atoms Benzene + oxygen atom Phenoxy Radical C6H5O Radical: Optical Electronic Transition B 2A2 ‹- X 2B1 2018/11/15

B 2A2 ‹- X 2B1 D D H matrix gas No vibrational assignment Radziszewski et al., 2001, J. Chem. Phys., 115, 9733 H matrix Ward, B., 1968, Spectrochim. Acta, Part A, 24, 813 gas No vibrational assignment No detail structure Cavity Ring Down Spectroscopy 2018/11/15

Results and Discussion Summary Introduction Experimental Results and Discussion Summary 2018/11/15

Experimental Anisole C6H5-OCH3 (0.1 torr) + He(1.0 Torr) Phenol C6H5-OH (0.1 torr) + He(1.0 Torr) Hollow Cathode Discharge 800 V 2018/11/15

Results and Discussion Summary Introduction Experimental Results and Discussion Summary 2018/11/15

⇒ Phenoxy Radical C6H5O D D H matrix gas This work gas Radziszewski et al., 2001, J. Chem. Phys., 115, 9733 matrix Ward, B., 1968, Spectrochim. Acta, Part A, 24, 813 gas Anisole C6H5-OCH3 Phenol C6H5-OH This work gas 2018/11/15 ⇒　Phenoxy Radical C6H5O

Observed spectrum v = 0 1 2 3 Progression ~500 cm-1 2018/11/15

Calculated frequencies in the B state by TD-B3LYP/cc-pVTZ Mode Number Symmetry Frequency (cm−1) 1 a1 3108 15 b1 954 2 3077 16 831 3 3055 17 743 4 1547 18 511 5 1521 19 399 6 1372 20 (10b) 94 7 1137 21 b2 3076 8 1005 22 3058 9 945 23 1564 10 786 24 1391 11 (6a) 501 25 1318 12 a2 946 26 1210 13 808 27 1143 14 322 28 986 29 578 30 419 2018/11/15

Vibrational structure 1 2 3 Progression ~500 cm-1 Franck-Condon simulation 6a 2018/11/15

Calculated Rotational Constants Rotational profile ? Calculated Rotational Constants in cm−1 B̃ 2A2 X̃ 2B1 A 0.1960 0.1851 B 0.0874 0.0935 C 0.0605 0.0621 (TD-)B3LYP/cc-pVTZ Rotational profile at 300 K ×Width ×Asymmetry 2018/11/15

Vibrational structure 2018/11/15

Vibrational structure Three components Lorentzian profile of 70 cm-1 Including small contribution of rational structure Lifetime of 0.1 ps in the B upper state 2018/11/15

Vibrational structure Sequence　? Δv = 0 sequence If yes, the profile depends on temperature. B Δv = 0 X 2018/11/15

Vibrational structure ? cm-1 Sequence　? 400 K Ribbon Heater 300 K Room Temp. 200 K Dry Ice B X 2018/11/15

Vibrational structure 200 K 300 K 2018/11/15

Vibrational structure 400 K 300 K 200 K B X 158±35 cm-1 2018/11/15

*No observational data Calculated frequencies in the X state by B3LYP/cc-pVTZ Mode Number Symmetry Frequency (cm−1) 20 (10b) b1 183* 14 a2 368* 30 b2 431* 19 469* 158±35 cm-1 in the X state 2018/11/15 *No observational data

Vibrational Structure 65 cm-1 10b 94 cm-1 Calculated Frequency in the B state TD-B3LYP/cc-pVTZ B ~118 cm-1 gradient X 183 cm-1 2018/11/15

Vibrational structures Progression of 6a Sequence of 10b 2018/11/15

Comparison with DIBs ▼ × Progression of 6a Sequence of 10b × Diffuse Clouds 3 K 2018/11/15

in diffuse cloud toward HD204827 Comparison with DIBs Hobbs et al. 2008, ApJ, 680, 1256 Band Width of C6H5O: 23Å Oscillator Strength: f = 0.0006 Theoretical Calculation (TD–B3LYP / cc–pVTZ) ▼ Upper limit of column density 9×1014 cm-2 in diffuse cloud toward HD204827 2018/11/15 Å

Summary Cavity Ring Down Spectroscopy of the B 2A2 – X 2B1 Transition of Phenoxy Radical Cavity Ring Down Spectrum of C6H5O Progression of 6a & Sequence of 10b Upper limit of column density 9×1014 cm-2 in diffuse cloud toward HD204827 Two fundamental benzene derivatives (C6H5S and C6H5O) were rejected as DIBs candidates. This study was funded by the Research Foundation for Opto-Science and Technology the Sumitomo Foundation Grant-in-Aid for Scientific Research on Innovative Areas (Grant No. 25108002) Institute for Quantum Chemical Exploration 2018/11/15

Thank you for your attention. 2018/11/15