The microwave spectroscopy of ground state CD3SH 72nd International Symposium on Molecular Spectroscopy @Univ. 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
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 16293-2422 (Parise et al. A&A 416 (2004) 159-163) Previous success of pseudo principal axis method (pseudo-PAM) to methyl formate in the second torsional excited state.
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
Previous microwave studies of CD3SH ・1955 T. Kojima, J. Phys. Soc. Jpn., 10 240. 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
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 30-50 mTorr at room temperature. Full coverage in 12-240 GHz. >37000 lines Estimated accuracy 100/50 kHz below and above 40 GHz.
The J = 4 ← 3 transitions of CD3SH in the ground state The asterisk denotes the unresolved K doublets.
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).
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
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!
The effective pseudo-PAM Hamiltonian The analysis using RAM was also carried out.
Part of molecular constants (vt=0) Pseudo-PAM RAM A 294076.(23) 62344.(58) B 10554.585(17) 10554.800(16) C 10197.776(58) 10197.765(58) DJ 0.0098342(11) 0.0098336(11) DJK 0.0951(36) 0.0945(36) dJ 0.00031407(10) 0.00031380(12) dK 0.0505(12) 0.0503(12) Dab - 249.29(60) F 12.4244(12) V3 436.032(58) 436.031(58) r 0.78876(11) q -587586.(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
Parameter transformation between RAM and pseudo-PAM
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 10554.585(17) 10554.805(17) C /MHz 10197.776(58) Dab /MHz -249.28(60) r 0.78876(11)
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
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!