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Terahertz spectroscopy of deuterated methylene bi-radicals, CHD and CD 2 Stéphane Bailleux stephane.bailleux@univ-lille1.fr June 25, 2015 – 70 th ISMS Meeting
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Contributor Toho University (THz) H. Ozeki acknowledgements Measurements
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Motivation Chemistry the parent carbene smallest polyatomic with triplet ground state key role in many chemical systems (astrochemistry) Spectroscopic challenges Theoretically light & floppy (breakdown of Watson Hamiltonian) difficult to treat quantum chemically and to predict levels Experimentally Highly reactive (towards hydrocarbons) most lines are in the THz or far-IR frequency regions
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CH 2, a key interstellar species Identified in hot cores in dense interstellar clouds A key intermediate in interstellar carbon chemistry C + + H 2 CH 2 + + hν CH 2 + + H 2 CH 3 + + H CH 3 + + e - CH 2 + H deuterium fractionation: CH 3 + + HD CH 2 D + + H 2 CH 2 D + + e - CHD + H or : CH 2 + D CHD 2 + + e - CHD + D or : CD 2 + H detection in Orion IRc2 ? Roueff et al. JPCA (2013)
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Hi-resolution rotational spectroscopy Far IR Laser Magnetic Resonance CH 2 ( 3 B 1 ) : 1982 CHD ( 3 A ʺ ) : 1994 CD 2 ( 3 B 1 ) : 1983 Microwave / Millimeter-wave isotopologue Number of pure rotational transitions f Max (THz) CH 20 62.0 CD 20 40.5 CHD0
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Millimeter-wave spectroscopy of CHD FIR – LMR observations our work Triplet ground state: |S| = 1 H SS = f (3 S a ² –S²) + β (S b ² –S c ²)
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Observation
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parameterCH 2 CHD MHzglobal analysisour workFIR-LMR rotation A 2 211 494.51 664 577(447) B 253 617.71170 344.047(3)170 233.7(21) C 215 102.79148 139.235(32)149 100.6(21) Δ K 87 644.2 42 060(498) Δ NK -615.15 -233.9(3) Δ N 11.082 5.905 δ N 3.2023 1.9 δ K 719.0 81.8 Φ K 7 042.119 1 907.6 Φ NK -0.5456 0.2 Φ KN -115.05 -32.7 fine structure aa 7 782.78 7562.1(25) 1 437.8121 339.584(75)1 382.0(75) (ε ab +ε ba )/2-59.96 ε aa 20.584-112.66(18)-105.527 ε bb -154.097-110.93(50) -83.342 ε cc -124.386-61. 2 Preliminary results (A&A 527, A64, 2011): more transitions planed to be measured: 1 11 ← 0 00 : ~1773 GHz 1 11 ← 2 02 : ~821 GHz
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CD 2 at THz frequency region (Toho Uni.) H. Ozeki (Toho Univ.) Production Pyrolysis (800 K / 1000 °F) of (CD 3 CO) 2 O (acetic anhydride-d 6 ) to produce CD 2 CO Mild discharge of CD 2 CO with Ar Low yield
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Example of spectrum 6 15 – 6 06, F3 : 1178335.324 MHz
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Example of spectrum 2 12 – 1 01, F2 : 1446874.340 MHz
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CD 2 at THz frequency region Current progress on measurements : 1 11 – 0 00 at 1.224, 1.228, 1.234 THz (Astronomically relevant) Current progress on measurements : 1 11 – 0 00 at 1.224, 1.228, 1.234 THz (Astronomically relevant) 7 16 – 7 07 at 1240 GHz 8 17 – 8 08 at 1316 GHz 9 09 – 8 18 at 1351 GHz The 3 fine-structure components have been observed for each 5
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CH 2 CD 2 global analysisour work rotation A 2 211 494.51 132 828.84(33) 000 B 253 617.71 126 805.934(95) 0 C 215 102.79 110 760.799(33) 0 Δ K 87 644.2 16 795.2 (FIR-LMR) Δ NK -615.15 -148.215 (32) Δ N 11.082 2.8264(39) δ N 3.2023 0.6531(10) δ K 719.0 83.4 (FIR-LMR) Φ K 7 042.119 588.0 (FIR-LMR) Φ NK -0.5456 -0.0832(10) Φ KN -115.05 -7.294 (FIR-LMR) fine structure 7 782.78 7 169.2(2)0 1 437.812 1 221.84(26) ε aa 20.584 9.56(29) ε bb -154.097 -76.512(73) ε cc -124.386 -62.43(13) Parameters (MHz)
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Concluding remarks Significant extension of number of lines measured (CD 2 ) 33 distinct transition frequencies (x 2) rms = 77 kHz More lines should be measured those astronomically relevant low N hyperfine-structure pattern (weak lines) but hyperfine parameters not known (CD 2 ) more efficient method of production required (CD 2 ) discharge in CD 4 samples (expensive) Paper in preparation
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Announcement Post-Doctoral Position Available at the University of Lille 1 year, starting from 01/2016 Net income : 2000 € Topic: spectroscopic detection of astronomically relevant species from the mmw to the THz frequency region Contact: stephane.bailleux@univ-lille1.fr
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Example of spectrum
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Millimeter-wave spectrometer (Toho) Precursor (CD 3 CO) 2 O
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N2N2 to pump LN 2 solenoid head pressure gauge parabolic mirror gas inlet anode cw power supply 5 kV / 600 mA BWO power suppl y 320 MHz 10 MHz PLL Feedback IF 12 -18 GHz local oscillator ~10 MHz Ref. oscillator 10 MHz Rb atomic clock Phase Sensitive Detector InSb Digital Oscilloscope phase modulation BWO pre- amplifier LN 2 -cooled absorption cell ballast Spectrometer (Lille Univ.)
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