1. The microwave spectroscopy of HCOO13CH3 in the second excited state
Submitted to J. Mol. Spectroscop.
Kaori Kobayashia, Takuro Kuwaharaa, Yuki Urataa, Nobukimi Ohashi,b Masaharu Fujitakeb
aDepartment of Physics, University of Toyama and
National Astronomical Observatory of Japan
bKanazawa University

2. Structure of methyl formate (HCOOCH3)b
Oxygen
13C
carbon
Hydrogen
Vt=0, E A
CH3-torsion
～135 cm-1
dipole moment　a-axis　1.63 D b-axis 0.68 D
Frequency (MHz)

3. Previous microwave studies of HCOO13CH3
□　R.F.Curl Jr, J. Chem. Phys. 30, 1529 (1959)
First laboratory microwave measurements including many isotopologues
□　 M.Carvajal et al. , Astron. Astrophys., 500, 3 (2009)
The extension of the ground state and identification in Orion.
□ I.Haykal et al. , Astron. Astrophys., 568, A58 (2014)
The assignment of the first torsional state and identification in Orion KL.

4. Analysis of normal methyl formate in different torsional states toward Orion KL
Sakai et al. ApJ. 803, 97 (2015)
It is likely to detect C 13 isotopolog in vt=2
Hot Core
Compact Ridge
Vt= Vt= Vt=2

5. Experiment
Spectrometer: Conventional source modulation spectrometer at the Univ. of Toyama
Sample Pressure: mTorr
Temperature: RT
Range: GHz
Estimated accuracy: 50 kHz

6. Sample preparation
Isotope enriched sample was synthesized by the following reaction in dimethyl sulfoxide
13CH3OH(>95%)+HCOOH -> HCOO13CH3+H2O
Sample quality was confirmed by NMR.

7. Example of Laboratory Spectra
Vt=2, A-species
Intensity (arb.units)
Frequency (MHz)

8. Assignment and analysis
Expected pattern similar to the normal species was searched for.
The assignments were confirmed by combination loops when possible.
Adoption of pseudo-PAM (principal axis method) which was successfully applied to the normal species.

9. The effective pseudo-PAM Hamiltonian

10. Vibrational energy levels of normal HCOOCH3 below 500 cm-1
E (cm-1)
CH3 torsion
200
300
100
400
Vt=1
Vt=2
Vt=3
Skeletal torsion
COC deform
Vt=4
358.0 cm-1
378.8 cm-1
318 cm-1
332 cm-1 A2 E A1 V3
Red colored energy levels: ab initio MO by Dr. Senent
White colored energy levels: low resolution experiment

11. ALMA science verification data
Orion KL band 6 is available.
12C/13C : 60
T: 100 K
N:Column density　1.17×1016 (cm2)
Favre et al , ApJ, 215, 25
FWHM 1.2 MHz

12. Simulation at the Compact Ridge (Orion KL)
SV data
simulation

13. Summary
More than 900 transitions of HCOO13CH3 in vt=2 were assigned and successfully analyzed with pseudo-PAM.
Our search in ALMA science verification data was not clear and further search is necessary.

14. Thank you for your attention!
Acknoledgment
T. Kuwahara
Y. Urata
M. Fujitake
N. Ohashi
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)
Thank you for your attention!