Laboratory rotational spectrum and astronomical search of Smethyl

Laboratory rotational spectrum and astronomical search of S-methyl thioformate A. Jabri, I. Kleiner, L. Margulès, R. Motyenko, J-C. Guillemin, E. A. Alekseev, B. Tercero and J. Cernicharo

Methyl formate: many lines detected in the interstellar medium E. Chruchwell and G. Winnewisser, Astron. Astrophys. , 45, 229 -231 (1975). S-methyl thioformate : MSCHO O-methyl thioformate : MOCHS

Astrophysical interest for sulfur bearing molecules Important for understanding the chemical evolution of hot cores; molecular ratios used as chemical clocks to get information about the age of hot cores (Charnley et al 1997, Wakelam et al 2004, 2011) BUT the chemistry of interstellar sulfur still undertermined: Much less sulfur found in the dense regions of ISM than in diffuse regions (Anderson et al 2013) Mystery about this missing sulfur, what are the reservoir(s) ? About 20 sulfur-containing molecules identified so far but very few with internal rotors : -CH 3 SH with observable A-E splittings (Linke et al 1979, Müller et al 2016) -Ethyl mercaptan CH 3 CH 2 SH in Orion (Kolesnikova et al 2014), no A-E splittings

Dimethyl ether: detected in the interstellar medium Snyder et al. , Astrophys. J. 191, L 79 -L 82 (1974). Search for dimethyl sulfur? So far without success in orion Jabri et al. , Astonom. And Astrophys. 589, A 127 (2016 DMS ? )

S- Methyl thiodformate CH 3 SCHO: Previous works • 1) Ab initio calculations Senent, Puzzarini, Hochlaf, Dominguez-Gomez, Carvajal, J. Chem. Phys 141, 104503 (2014)

q (degrees) a (degrees) Senent, Puzzarini, Hochlaf, Dominguez-Gomez, Carvajal, J. Chem. Phys 2014

Chemical synthesis of S-methyl thioformate J-C Guillemin (Rennes) and A. Jabri Methyl mercaptan (or methanethiol) Formic-acetic Anhydride

S- Methyl thiodformate CH 3 SCHO: Previous works 2) Microwave measurements a) Jones et al 1976, J. Mol. Spectrosc. 60, 348 b) 22 A type lines and 15 E type lines fit to a few MHz 10 – 41 GHz

New millimeter measurements in Lille

Analysis of the spectrum of S-methyl thioformate Previous experimental data measured by Jones et al. and by Caminati et al. was fit between 10 GHz and 41 GHz. We used the BELGI-Cs program in order to optimize different rotational constants. , 2256 new millimeter lines assigned with J and Ka values up to 70 and 30, vt = 0

Results: fits for the S-methyl thioformate vt=0 (BELGI-Cs) Number of lines Weight (in k. Hz) rms (in k. Hz) Microwave data from Caminati et al (1981) 51 150 91 Millimeter data New measurements 2137/ 117 /2 45/100/150 27. 8/84. 6/90. 6 Total: 2307 lines fit to 35. 6 k. Hz J and Ka values up to 70 and 30 34 parameters

Conclusion 2307 lines of the ground torsional state vt = 0 -0 methyl thioformate fit to 35. 6 k. Hz, J and Ka values up to 70 and 30 A prediction of line positions and intensites is ready for astrophyscical search

Work in progress: Experimental spectrum recorded for the Omethyl thioformate 14 Millimeter spectrum(Lille) between 150 and 330 GHz: 849 lines assigned, Preliminary fit Marion Kirmann Stage filé février-mai 2016 25/05/2016

Aknowledgments: A. Jabri would like to thank the french groupe de recherche SPECMO for travel grant to Lille We thank the french Programme de Physique et Chimie du Milieu Interstellaire (PCMI) for funding