A SIMULTANEOUS FIT OF vt = 0 AND 1 TORSION-WAGGING-ROTATIONAL LEVELS OF METHYLAMINE USING A HYBRID (TUNNELING AND NON-TUNNELING) HAMILTONIAN FORMALISM

This work is in memory of Dr. Jon Hougen deceased on January 28th 2019 who dedicated his life to spectroscopy and worked on the present project very actively untill the end of December 2018. We will show the latest results obtained with Jon on the fit of more than 15000 rotational-torsional-wagging transitions in the MW and FIR of v$_{t}$ = 0,1 of \chem{CH_3NH_2}. We used the recently written hybrid program to fit rotational levels in molecules with one \chem{CH_3} internal-rotation large-amplitude motion, one \chem{NH_2} inversion large-amplitude motion, and symmetry described by the G$_{12}$ PI group\footnote{J. T. Hougen and I. Kleiner, J. Phys. Chem. A, 2015, 119, 10664}. We will first present an overview of our present best least-squares fit. The data set contains slightly less than 2500 MW and 12754 FIR transitions, which are fit to a weighted standard deviation of 1.13 using 74 parameters. Most of the FIR transitions are taken from recent measurements of the v$_{t}$ = 1-0 band centered near 265 \wn \footnote{I. Gulaczyk, M. Kreglewski, V.-M. Horneman, J. Mol. Spectrosc. 2017,342, 25}, but a number of lines were re-assigned or remeasured. The ground torsional state (taken mostly from Motyienko et al\footnote{R.A. Motiyenko, V.V. Ilyushin, B.J. Drouin, S. Yu, L. Margulès, Astron.and Astrophys. 2014, 563, A1}) fit within measurement uncertainty but 75 older MW measurements in the v$_{t}$ = 1 showed large observed-calculated residuals and were presently discarded from the fit. We believe that our fit, as well as the predictive abilities of the program, are now sufficiently good that we can begin a new measurement campaigns of v$_{t}$ = 1 MW data and v$_{t}$ = 2, 3 IR data. This new project will be discussed in the talk\footnote{Part of this work has been funded by the Programme National de Physique Chimie du Milieu Interstellaire (PCMI)}