Laboratory Optical Spectroscopy of the Phenoxy Radical as

Laboratory Optical Spectroscopy of the Phenoxy Radical as a Diffuse Interstellar Bands Candidate Tokyo Univ. Science Mitsunori Araki, Yuki Matsushita, Koichi Tsukiyama 2022/1/19 2015/06/25 1

Diffuse Interstellar Bands n Optical absorption lines by molecules in diffuse cloud Electronic Transition A or B Absorption ★ X Diffuse Cloud n n 2022/1/19 n Near infrared ~ optical (line width: 0. 5 -50Å) First report: 1922 ~600 lines 2

What are origins of DIBs ? Optical Transition Ion and/or radical Large Molecule Not Identified yet Identification of DIBs 2022/1/19 3

How to identify DIBs ? Optical Electronic Transition Space Star Lab Earth absorption Unidentified molecule Molecule Spectrometer Discharge etc. Spectra Identification 2022/1/19 DIB fit 4

Cavity Ring Down Spectrometer Hollow Cathode Discharge Pulsed dye laser, Dn = 0. 2 cm-1, 10 Hz Discharge cell Laser - G Electrodes 2022/1/19 Detector Absorption 5

n Polyaromatic Hydrocarbon (PAH) n 10% of interstellar molecules have a sulfur atom Benzene + sulfur atom Thiophenoxy Radical C 6 H 5 S Radical: Optical Electronic Transition B 2 A 2 ‹- X 2 B 1 2022/1/19 Wavelength /Å 6

la Ga HD 204827 c i ct e an Pl HD 204827 Celestial North Pole HD 204827 The ８ th Magnitude Star 380 DIBs Hobbs et al. 2008 ★ 2022/1/19 HD 204827 Observer 7

Comparison with DIBs HD 204827 No fit Upper limit of column density: 2× 1013 cm-2 Wavelength /Å This meeting in 2014 2022/1/19 Araki et al. , 2014, Astronomical J. , 148, 87 8

n Polyaromatic Hydrocarbon (PAH) n 30% of interstellar molecules have oxygen atoms Benzene + oxygen atom Phenoxy Radical C 6 H 5 O Radical: Optical Electronic Transition B 2 A 2 ‹- X 2 B 1 2022/1/19 9

B 2 A 2 ‹- X 2 B 1 D D Radziszewski et al. , 2001, J. Chem. Phys. , 115, 9733 H matrix Ward, B. , 1968, Spectrochim. Acta, Part A, 24, 813 No vibrational assignment No detail structure 2022/1/19 gas Cavity Ring Down Spectroscopy 10

n Introduction n Experimental n Results and Discussion n Summary 2022/1/19 11

Experimental Anisole C 6 H 5 -OCH 3 (0. 1 torr) Phenol C 6 H 5 -OH (0. 1 torr) + He(1. 0 Torr) Hollow Cathode Discharge 800 V 2022/1/19 12

n Introduction n Experimental n Results and Discussion n Summary 2022/1/19 13

D H Radziszewski et al. , 2001, J. Chem. Phys. , 115, 9733 matrix gas Ward, B. , 1968, Spectrochim. Acta, Part A, 24, 813 This work gas 2022/1/19 Anisole C 6 H 5 -OCH 3 Phenol C 6 H 5 -OH ⇒ Phenoxy Radical C 6 H 5 O 14

Observed spectrum v=0 1 2 3 Progression ~500 cm-1 2022/1/19 15

Calculated frequencies in the B state by TD-B 3 LYP/cc-p. VTZ Mode Number Symmetry 1 a 1 Mode Number Symmetry 3108 15 b 1 2 3077 16 831 3 3055 17 743 4 1547 18 511 5 1521 19 399 6 1372 20 (10 b) 7 1137 21 8 1005 22 3058 9 945 23 1564 10 786 24 1391 11 (6 a) 501 25 1318 946 26 1210 13 808 27 1143 14 322 28 986 29 578 30 419 12 2022/1/19 a 2 Frequency (cm− 1) 954 94 b 2 3076 16

Vibrational structure v=0 1 2 3 Progression ~500 cm-1 Franck-Condon simulation 6 a 2022/1/19 17

Rotational profile ? Calculated Rotational Constants in cm− 1 B 2 A 2 X 2 B 1 A 0. 1960 0. 1851 B 0. 0874 0. 0935 C 0. 0605 0. 0621 (TD-)B 3 LYP/cc-p. VTZ Rotational profile at 300 K ×Width ×Asymmetry 2022/1/19 18

Vibrational structure 2022/1/19 19

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 2022/1/19 20

Vibrational structure Sequence ? n n Δv = 0 sequence If yes, the profile depends on temperature. 2022/1/19 B Δv = 0 X 21

Vibrational structure Sequence ? n n n 400 K Ribbon Heater 300 K Room Temp. 200 K Dry Ice B X ? cm-1 2022/1/19 22

Vibrational structure 200 K 2022/1/19 300 K 23

Vibrational structure 400 K 300 K 200 K B X 158± 35 cm-1 2022/1/19 24

Calculated frequencies in the X state by B 3 LYP/cc-p. VTZ Mode Number Symmetry Frequency (cm− 1) 20 (10 b) b 1 183* 14 30 19 2022/1/19 a 2 b 1 368* 158± 35 cm-1 in the X state 431* 469* *No observational data 25

Vibrational Structure 65 cm-1 Calculated Frequency in the B state TD-B 3 LYP/cc-p. VTZ B 10 b 94 cm-1 ~118 cm-1 X 183 cm-1 2022/1/19 26

Vibrational structures Progression of 6 a Sequence of 10 b 2022/1/19 27

Comparison with DIBs Progression of 6 a ▼ × × × ▼ × × Sequence of 10 b Diffuse Clouds 3 K 2022/1/19 28

Comparison with DIBs Hobbs et al. 2008, Ap. J, 680, 1256 n Band Width of C 6 H 5 O: 23Å n Oscillator Strength: f = 0. 0006 Theoretical Calculation (TD–B 3 LYP / cc–p. VTZ) ▼ 2022/1/19 Upper limit of column density 9× 1014 cm-2 in diffuse cloud toward HD 204827 Å 29

Summary Cavity Ring Down Spectroscopy of the B 2 A 2 – X 2 B 1 Transition of Phenoxy Radical n Cavity Ring Down Spectrum of C 6 H 5 O n Progression of 6 a & Sequence of 10 b n n Upper limit of column density 9× 1014 cm-2 in diffuse cloud toward HD 204827 Two fundamental benzene derivatives (C 6 H 5 S and C 6 H 5 O) were rejected as DIBs candidates. This study was funded by n the Research Foundation for Opto-Science and Technology n the Sumitomo Foundation n Grant-in-Aid for Scientific Research on Innovative Areas (Grant No. 25108002) 2022/1/19 n Institute for Quantum Chemical Exploration 30

Thank you for your attention. 2022/1/19 31