The effects of proton tunneling, 14N quadrupole coupling, and methyl internal rotations in the microwave spectrum of ethyl methyl amine

The Journal of Chemical Physics, vol. 153, pp. 184308

Abstract

The spectra of N-ethyl methyl amine, CH3(NH)CH2CH3, were measured using a molecular jet Fourier transform microwave spectrometer in the frequency range of 2 GHz–26.5 GHz. Splittings due to proton inversion tunneling, Coriolis coupling, 14N quadrupole coupling, and methyl internal rotation were fully resolved. The experimentally deduced rotational constants are A = 25 934.717(21) MHz, B = 3919.8212(23) MHz, and C = 3669.530(21) MHz. The proton tunneling causes (+) ↔ (−) splittings of about 1980.9 MHz for all c-type transitions between the lowest symmetric and the higher anti-symmetric energy levels. The splittings of the (+) ← (+) and (−) ← (−) levels, mainly influenced by Coriolis coupling, were also observed and assigned for b-type transitions, yielding the coupling constants Fbc = 0.3409(71) MHz and Fac = 163.9(14) MHz. The 14N quadrupole coupling constants were determined to be χaa = 2.788 65(55) MHz and χbb − χcc = 4.630 45(91) MHz. Fine splittings arising from two inequivalent methyl rotors are in the order of 150 kHz, and the torsional barriers are determined to be 1084.62(41) cm−1 for the CH3NH methyl group and 1163.43(80) cm−1 for the CH2CH3 methyl group. The experimental results are in good agreement with those of quantum chemical calculations.

Authors 3

1. Kenneth J. Koziol Aachen Institute of Physical Chemistry

   RWTH Aachen University · Institut Universitaire de France

   Affiliation as printed

   Institute of Physical Chemistry, RWTH Aachen University 1 , Landoltweg 2, 52074 Aachen, Germany

   3Institut Universitaire de France (IUF), 1 Rue Descartes, 75231 Paris Cedex 05, France

2. Wolfgang Stahl Aachen Institute of Physical Chemistry

   RWTH Aachen University · Institut Universitaire de France

   Affiliation as printed

   Institute of Physical Chemistry, RWTH Aachen University 1 , Landoltweg 2, 52074 Aachen, Germany

   3Institut Universitaire de France (IUF), 1 Rue Descartes, 75231 Paris Cedex 05, France

3. Ha Vinh Lam Nguyen corresponding Aachen 1Institute of Physical Chemistry

   RWTH Aachen University · Centre National de la Recherche Scientifique · Institut Universitaire de France · Université Paris-Est Créteil · Laboratoire Interuniversitaire des Systèmes Atmosphériques · Institut Pierre-Simon Laplace

   Affiliation as printed

   Institut Universitaire de France (IUF) 3 , 1 Rue Descartes, 75231 Paris Cedex 05, France

   Laboratoire Interuniversitaire des Systèmes Atmosphériques (LISA), CNRS UMR 7583, Université Paris-Est Créteil, Université de Paris, Institut Pierre Simon Laplace 2 , 61 Avenue du Général de Gaulle, 94010 Créteil, France

   1Institute of Physical Chemistry, RWTH Aachen University, Landoltweg 2, 52074 Aachen, Germany