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\title{THE FIRST TORSIONALLY EXCITED STATE OF METHYLAMINE: ROTATIONAL SPECTRUM AND INTERSTELLAR DETECTION}

\author{\FirstName P. \LastName GYAWALI, \FirstName R. A. \LastName MOTIYENKO}
\address{UMR 8523 - PhLAM - Physique des Lasers Atomes et Molecules, University of Lille, CNRS, F-59000 Lille, France}

\author{\FirstName A. \LastName BELLOCHE}
\address{Millimiter und Submillimeter-Astronomie, Max-Planck-Institut fur Radioastronomie, Bonn, NRW, Germany}

\author{\underline{\FirstName I. \LastName KLEINER}}
\address{Universit\'e Paris Cit\'e and Univ Paris Est Cr\'eteil, CNRS, LISA, 75013, Paris France}

\author{\FirstName V. \LastName ILYUSHIN, \FirstName E.~A. \LastName ALEKSEEV}
\address{Radiospectrometry Department, Institute of Radio Astronomy of NASU,
Kharkov, Ukraine}

\author{\FirstName I. \LastName  GULACZYK, \FirstName M. \LastName KREGLEWSKI}
\address{Faculty of Chemistry, Adam Mickiewicz University, Poznan, Poland}


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Methylamine (CH$_{3}$NH$_{2}$) exhibits two large amplitude motions, methyl torsion and amine wagging, that complicate the spectral analysis especially in excited vibration states. To deal with the problem of fitting spectra in excited torsional states in the molecules like methylamine a new so-called 'hybrid' Hamiltonian model was developed not far ago.\footnote{Kleiner, I. and Hougen, J. T. 2015, J. Phys. Chem. A, 119, 10664} Our current work aims to study experimentally and theoretically the terahertz rotational spectrum of methylamine to provide a reliable basis for the ISM detection of rotational transitions in v$_{t}$ = 1 state. In its v$_{t}$ = 0 state methylamine was first detected in the interstellar medium (ISM) toward Sgr B2 almost 50 years ago.\footnote{Kaifu, et al. 1974, ApJ, 191, L135; Fourikis et al. 1974, ApJ, 191, L139} The terahertz spectrum of methylamine was measured from 150 to 1520 GHz with the Lille fast scan spectrometer. Using a new hybrid Hamiltonian model,
 we were able to fit accurately the rotational spectrum of the v$_{t}$= 1 state of methylamine including the analysis of the nuclear quadrupole hyperfine
 structure. The results of this spectroscopic analysis allowed us to search for rotational transitions of methylamine in its first torsionally excited state
 toward the high-mass star forming region Sgr B2(N) that was the target of the imaging spectral line survey ReMoCA performed with the Atacama Large 
Millimeter/submillimeter Array (ALMA). We report the first interstellar detection of methylamine in its v$_{t}$ = 1 state on the basis of this 
interferometric data set. Also, further steps in fitting the rotational transitions in the second torsional state of methylamine v$_{t}$= 2 will be shown.

This project has been supported by ANR Labex CaPPA through the PIA under Contract No. ANR-11-LABX-0005-01. This work was also supported by the Programme National de Physique et Chimie du Milieu Interstellaire (PCMI) of CNRS/INSU with INC/INP co-funded by CEA and CNES.

       
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