1. 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

2. 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: Å)
First report: 1922
~600 lines
2018/11/15

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

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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

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

12. 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

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

14. ⇒ 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

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

16. 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

17. Vibrational structure1 2 3
Progression
~500 cm-1
Franck-Condon
simulation 6a
2018/11/15

18. 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

19. Vibrational structure
2018/11/15

20. 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

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

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

23. Vibrational structure
200 K
300 K
2018/11/15

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

25. *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

26. 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

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

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

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

30. 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 )
Institute for Quantum Chemical Exploration
2018/11/15

31. Thank you for your attention.
2018/11/15