Terahertz spectroscopy of deuterated
methylene bi-radicals, CHD
and CD2
Stéphane Bailleux
stephane.bailleux@univ-lille1.fr
June 25, 2015 – 70th ISMS Meeting
Contributor
Measurements
 Toho University (THz)
H. Ozeki
 acknowledgements
Motiv ation
 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
CH2 , a key interstellar species
 Identified in hot cores in dense interstellar clouds
 A key intermediate in interstellar carbon chemistry
C+
+ H2  CH2+ + hν
CH2+ + H2  CH3+ + H
detection in Orion IRc2 ?
Roueff et al. JPCA (2013)
CH3+ + e-  CH2 + H
d e u t e r i u m f r a c t i o n a t i o n : CH3+ + HD  CH2D+ + H2
CH 2 D + + e -  CHD + H
or :
CH 2 + D
CHD 2 + + e -  CHD + D
or :
CD 2 + H
Hi-resolution rotational spectroscopy
 Far IR Laser Magnetic Resonance
CH2 (3B1) : 1982
CHD (3Aʺ) : 1994
CD2 (3B1) : 1983
 Microwave / Millimeter-wave
isotopologue Number of pure rotational transitions
CH20
CD20
6
4
CHD
0
f Max (THz)
2.0
0.5
Millimeter-wave spectroscopy of CHD
Triplet ground state: |S| = 1
HSS =  f(3 Sa² –S²) + β (Sb² –Sc²)
Observation
parameter
CH2
CHD
MHz
global analysis
our work
FIR-LMR
rotation
A
2 211 494.5
1 664 577(447)
B
253 617.71
170 344.047(3)
170 233.7(21)
C
215 102.79
148 139.235(32) 149 100.6(21)
42 060(498)
ΔK
87 644.2
-233.9(3)
ΔNK
-615.15
5.905
ΔN
11.082
Preliminary results (A&A 527,
1.9A64, 2011):
δN
3.2023
81.8
δK
719.0
more transitions planed to be
measured:
1
907.6
ΦK
7 042.119
111 ← 000 : ~17730.2
GHz
ΦNK
-0.5456
-32.7
ΦKN
-115.05
111 ← 202 : ~821 GHz
fine structure
7 782.78
a
7562.1(25)
bb
1 437.812
1 339.584(75)
1 382.0(75)
(εab +εba)/2
-59.96
εaa
20.584
-112.66(18)
-105.527
εbb
-154.097
-110.93(50)
-83.342
εcc
-124.386
-61. 2
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
Example of spectrum
615 – 606 , F3 : 1178335.324 MHz
Example of spectrum
212 – 101 , F2 : 1446874.340 MHz
CD 2 at THz frequency region
5
Current progress on measurements :
111 – 0 00 at 1.224 , 1.228 , 1.234 THz
(Astronomically relevant)
7 16 – 7 07 at 1240 GHz
The
8 173 –fine-structure
8 08 at 1316 GHz
components have been
9 09 – 8 18for
at each
1351 GHz
observed
Parameters (MHz)
CH2
global analysis
rotation
A
B
C
ΔK
ΔNK
ΔN
δN
δK
ΦK
ΦNK
ΦKN
fine structure

b
εaa
εbb
εcc
2 211 494.5
253 617.71
215 102.79
87 644.2
-615.15
11.082
3.2023
719.0
7 042.119
-0.5456
-115.05
7 782.78
1 437.812
20.584
-154.097
-124.386
CD2
our work
1 132 828.84(33)000
126 805.934(95) 0
110 760.799(33) 0
16 795.2 (FIR-LMR)
-148.215 (32)
2.8264(39)
0.6531(10)
83.4 (FIR-LMR)
588.0 (FIR-LMR)
-0.0832(10)
-7.294 (FIR-LMR)
7 169.2(2)0
1 221.84(26)
9.56(29)
-76.512(73)
-62.43(13)
Concluding remarks
 Significant extension of number of lines measured
(CD2)
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 (CD2)
 more efficient method of production required (CD2)
discharge in CD4 samples (expensive)
 Paper in preparation
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
Example of spectrum
Millimeter-wave spectrometer (Toho)
Precursor (CD3CO)2O
Spectrometer (Lille Univ.)
gas inlet
cw power supply
5 kV / 600 mA
parabolic
mirror
anode
ballast
N2
LN2
solenoid
LN2-cooled absorption cell
12 -18 GHz
local oscillator
10 MHz
Rb atomic
clock
~10 MHz
Ref. oscillator
to pump
320 MHz
InSb
preamplifier
phase
modulation
BWO
BWO
power supply
head pressure
gauge
 10 MHz PLL

Feedback
 IF
Phase
Sensitive
Detector
Digital
Oscilloscope