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

Structure of methyl formate (HCOOCH3) b Oxygen 13C carbon Hydrogen Vt=0, 20 1 19 -19 1 18 E A CH3-torsion ～135 cm-1 dipole moment　a-axis　1.63 D b-axis 0.68 D Frequency (MHz)

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.

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=0 Vt=1 Vt=2

Experiment Spectrometer: Conventional source modulation spectrometer at the Univ. of Toyama Sample Pressure: 30- 50 mTorr Temperature: RT Range: 50-321.7 GHz Estimated accuracy: 50 kHz

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.

Example of Laboratory Spectra 18 1 18 -17 1 17 18 0 18 -17 0 17 Vt=2, A-species Intensity (arb.units) 18 1 18 -17 0 17 18 0 18 -17 1 17 Frequency (MHz)

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.

The effective pseudo-PAM Hamiltonian

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

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. 2014 , ApJ, 215, 25 FWHM 1.2 MHz

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

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.

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!