1. The microwave spectroscopy of ground state CD3SH
72nd International Symposium on Molecular Illinois, Urbana-Champagne
The microwave spectroscopy of ground state CD3SH
J. Mol. Spectroscop., Article in press
Kaori Kobayashia,b, Wataru Nakamuraa, Tatsuro Matsushimaa, Shozo Tsunekawaa, and Nobukimi Ohashic
aDepartment of Physics, University of Toyama
bNational Astronomical Observatory of Japan
cKanazawa University
Jun. 20th 2017

2. Background
Methyl mercaptan (methanethiol) is known interstellar molecule which contains sulfur.
Deuterated methanol has been found in interstellar space despite the fact of low cosmic abundance of deuterium.
CD3OH towards the low-mass protostar IRAS (Parise et al. A&A 416 (2004) )
Previous success of pseudo principal axis method (pseudo-PAM) to methyl formate in the second torsional excited state.

3. Internal rotation potential of methyl mercaptan
Vt=0、A
Vt=0、E
Vt=1、E
Vt=1、A
Vt=2、A
Vt=2、E
Barrier height
V3=435ｃｍ－１
Angle of internal rotation
dipole moment　a-axis 1.33 D b-axis 0.71 D
Torsion fundamental
about 130 cm-1

4. Previous microwave studies of CD3SH
・1955　T. Kojima, J. Phys. Soc. Jpn.,
First laboratory identification
many other studies on the ground states
・1983 Kimura, Toyama University Master’s thesis
9-65 GHz with Stark spectrometer
dipole moment
・1989 Hayashi , Toyama University Master’s thesis
The first and second torsional excited states

5. Experiment
Conventional Stark/source modulation spectrometer was used for the experiment.
The isotope enriched sample was purchased and used without further purification.
The pressure was mTorr at room temperature.
Full coverage in GHz. >37000 lines
Estimated accuracy 100/50 kHz below and above 40 GHz.

6. The J = 4 ← 3 transitions of CD3SH in the ground state
The asterisk denotes the unresolved K doublets.

7. Assignment and analysis
Predictions by using results of the RAM analysis.
Polynomial expansion of a series and intensity also helped the assignment.
The assignments were confirmed by Stark shift or combination loops when possible.
Adoption of pseudo-PAM for large r (internal rotation parameter).

8. Coordinate systems for internal rotation problems
Hougen, Kleiner, & Godefroid, J. Mol. Spectrosc., 163, 559 (1994)
Principal axis method
Rho axis method
PAM
RAM
Elimination of the Jx terms

9. Coordinate systems for internal rotation problems
Hougen, Kleiner, & Godefroid, J. Mol. Spectrosc., 163, 559 (1994)
Pseudo-PAM
Successful application to the methyl formate in vt=2
Capability of doing global analysis
Principal axis method
Rho axis method
Pseudo-principal axis method
PAM
RAM
Pseudo-PAM
Elimination of the Jx terms
Elimination of the (Jz Jx +Jx Jz ) term
No large JxJz cross terms!

10. The effective pseudo-PAM Hamiltonian
The analysis using RAM was also carried out.

11. Part of molecular constants (vt=0)
Pseudo-PAM
RAM A
(23)
62344.(58) B
(17)
(16) C
(58)
(58) DJ
(11)
(11)
DJK
0.0951(36)
0.0945(36) dJ
(10)
(12) dK
0.0505(12)
0.0503(12)
Dab
(60) F
(12) V3
(58)
(58) r
(11) q
(59)
-516.6(12)
Units in MHz except F and V3 which are in cm-1
1s errors
1065 transitions
(484 A-species and 581 E-species)
Jmax=46
Kmax=10
rms=0.104 kHz
22 parameters
Same quality of fit for both pseudo-PAM and RAM

12. Parameter transformation between RAM and pseudo-PAM

13. Rotational and internal-rotational parameters in the pseudo-PAM and RAM systems for CD3SH in vt = 0
pseudo-PAM
RAM
A /MHz
294076(23)
62344(58)
B /MHz
(17)
(17)
C /MHz
(58)
Dab /MHz
(60) r
(11)

14. Summary and future work
Over 1000 transitions of CD3SH were successfully analyzed with pseudo-PAM.
The capability to apply this method to the large r case.
Global analysis of vt=0 and 1

15. Thank you for your attention!
Acknoledgment
Funding
National Astronomical Observatory of Japan (NAOJ) ALMA-J
Grant-in-Aid for Scientific Research by the Ministry of Education, Culture, Sports, Science, and Technology of Japan (Grant No. 15H03646)
W. Nakamura (Master)
T. Matsushima (Master)
S. Tsunekawa
N. Ohashi
Thank you for your attention!