Electronic Transition Spectra of Thiophenoxy and Phenoxy Radicals in Hollow cathode discharges

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1 Electronic Transition Spectra of Thiophenoxy and Phenoxy Radicals in Hollow cathode discharges Tokyo Univ. Science Mitsunori ARAKI, Hiromichi WAKO, Kei NIWAYAMA and Koichi TSUKIYAMA 2014/06/ /2/20 1

2 Diffuse Interstellar Bands Electronic Transition A or B Absorption X Optical absorption lines by molecule in diffuse cloud Near infrared ~ optical (line width: Å) First report: 1922 ~600 lines Diffuse Cloud 2015/2/20 2

3 What are origins of DIBs? Optical Transition Ion and/or radical Large Molecule Not Identified yet Identification of DIBs by Laboratory Spectroscopy 2015/2/20 3

4 How to identify DIBs? Optical Electronic Transition Space absorption Earth Star Lab Unidentified molecule Molecule DIB Spectrometer Discharge etc Spectra Identification fit 2015/2/20 4

5 Cavity Ring Down Spectrometer Pulsed dye laser, 10 Hz, ν = 0.1 cm -1 Hollow Cathode Discharge Discharge cell - G Electrodes 2015/2/20 5

6 Thiophenoxy Radical C 6 H 5 S Rotational Profile Model molecule to discuss Non-Boltzmann Distribution in diffuse cloud Radical: Optical Transition 10% of interstellar molecules -> Sulfide Simple PAH Good candidate of DIB Dose it fit to DIBs? 2015/2/20 6

7 Reported Laboratory Spectrum Electronic Transition 2 A 2 - X 2 B 1 DIBs LIF Disturbed Origin Shibuya et al., Chemical Physics, 121, , /2/20 7

8 Galactic Plane HD having DIBs Celestial North HD Pole HD The 8th Magnitude Star 2015/2/20 8

9 DIBs and Reported Laboratory Spectrum HD DIBs Wavelength (Å) 2015/2/20 9 Hobbs et al., ApJ, 680, 1256 (2008)

10 DIBs and Present Laboratory Spectrum by CRD HD DIBs High Temperature Rotational Profile 300K C 6 H 5 SH 1000V Wavelength (Å) 2015/2/20 10 Hobbs et al., ApJ, 680, 1256 (2008)

11 Analysis of C 6 H 5 S Rotational Profile Rotational Constants Simulation of Non-Boltzmann Distribution in Diffuse Cloud Simulation of Rotational Profile in Diffuse Cloud Comparison with DIBs 2015/2/20 11

12 Rotational Constants from Rotational Profile 300K (cm -1 ) B3LYP/cc-pVTZ A B C A = = = = ( ) B+ C = T = ( 3) ( ) Wavelength (Å) Pgopher 2015/2/20 12

13 Non-Boltzmann Distribution in Diffuse Cloud Dark Clouds Diffuse Clouds Collision >> Radiation Less Collision + Radiation T r = 2.73 K T k = 100K Linear Molecule Oka et al., 2013, ApJ, 773, 42O T r = 14.6 K T r = 80 K 2015/2/20 13

14 Non-Boltzmann Distribution in Diffuse Cloud Dark Clouds Diffuse Clouds Collision >> Radiation Less Collision + Radiation T r = 2.73 K T k = 100K Linear Molecule Oka et al., 2013, ApJ, 773, 42O T r = 14.6 K T r = 80 K C 2v Asymmetric Top Singlet 2015/2/20 14

15 Rotation of C 2v Asymmetric Top J (K c ) K a Permanent dipole moment 2015/2/20 15

16 Boltzmann Distribution Collision >> Radiation Dark Clouds J = 3 J = 2 J = 1 High temperature Low temperature J = 0 K a = 0 K a = 1 K a = 2 K a = /2/20 16

17 Rotation of C 2v Asymmetric Top Radiative Cooling a-type J (K c ) Diffuse Clouds K a No Radiative Cooling Permanent dipole moment 2015/2/20 17

18 Distribution in Diffuse Cloud Collision + Radiation (a-type) Diffuse Clouds J = 3 J = 2 K a = 0 High temperature Low temperature J = 1 J = 0 K a = 0 K a = 1 K a = 2 K a = /2/20 18

19 Rotation of C 2v Asymmetric Top Slow Down J (K c ) Diffuse Clouds K a Hot Axis Continuous Rotation Permanent dipole moment 2015/2/20 19

20 Analysis of C 6 H 5 S Rotational Profile Rotational Constants Simulation of Non-Boltzmann Distribution in Diffuse Cloud Simulation of Rotational Profile in Diffuse Cloud Pgopher Comparison with DIBs 2015/2/20 20

21 2.73 K Non-Boltzmann distribution is important in diffuse clouds. HD Rotational Profile in diffuse cloud Collision 40 K Radiation 2.73 K Collision 40 K Wavelength /Å 2015/2/20 21

22 Distribution in Diffuse Cloud Collision + Radiation (a-type) Diffuse Clouds J = 3 J = 2 K a = ±2 K a = 0 J = 1 J = 0 K a = 0 K a = 1 K a = 2 K a = /2/20 22

23 Distribution in Diffuse Cloud Collision + Radiation (a-type) Diffuse Clouds A( K a = 0) > A( K a = ±2) ~ Collision The profile can depend on this competition. 2015/2/20 23

24 2.73 K Rotational Profile in diffuse cloud HD Collision 40 K Radiation 2.73 K Narrower limit Wider limit Wavelength /Å 2015/2/20 24

25 Comparison with DIBs No fit No detection HD Wavelength /Å 2015/2/20 25

26 Upper Limit of Column Density Simulation of Rotational Profile Band Width of C 6 H 5 S: 2Å Theoretical Calculation (TD B3LYP / cc pvtz) Oscillator Strength: f = HD204827, Hobbs et al., ApJ, 680, 1256 (2008) Detection threshold: S/N = 5 Upper limit of column density cm /2/20 26

27 Summary Electronic Spectrum of Thiophenoxy Radical C 6 H 5 S By Cavity Ring Down Spectroscopy Simulation of Rotational Profile in Diffuse Cloud Upper limit of column density cm -2 Non-Boltzmann distribution is important in diffuse cloud. 2015/2/20 27

28 2015/2/20 28

29 Einstein Coefficients and Oka Coefficient (1973) J B ρ n(j) B ρ A C C J-1 n(j-1) n ( )( ) ( )( ) J J A B ρ+ C = nj B ρ C + J 1 J 1 1 J 1 + J /2/20 29

30 n Rotational Distribution Linear n ( J) = n( 0) J m= 1 Asym top 2 αb µ J ( ) ( ) 2m 1exp( 2hBm ktr) J = n0 m= K a m αb µ 2m 1exp m αb µ 1+ 2m+ 1 exp + 1 αb 3 3 m 3 S 3 2 ms µ 1+ 2m+ 1 exp 1 ( 2hBmkT ) ( 2hBmkT ) ( 2hBm kt ) 2m+ 1 + C exp 1 2m 1 2m 1 + C exp 2m+ 1 r 1 ( hbm kt ) ( hbm kt ) Radiation temp. (dust) T r = 40 K Kinetic (collisional) temp. (H 2 ) T k = 2.73 K Oka s Collisional Coefficient C = 10E-7 Rotational Constant B = 1454 MHz Permanent Dipole Moment µ = 3.1 D 2015/2/ r 2m+ 1 + C exp 1 2m 1 2m 1 + C exp r 1 2m+ 1 ( hbmkt ) k ( hbmkt ) k k k

31 What parameters are determining the rotational profile? With a hot axis or not. With a permanent dipole moment or not. Radiation temperature T r Kinetic temperature T k C constant Permanent dipole moment Rotational constants Rotational constants difference Lifetime 2015/2/20 31