Stuttgart 2012 – scientific programme
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MO: Fachverband Molekülphysik
MO 5: Experimental Techniques
MO 5.9: Talk
Monday, March 12, 2012, 18:30–18:45, V38.02
Nitrogen inversion tunneling in the microwave spectrum of diethyl amine and methyl tert-butyl amine — •Ha Vinh Lam Nguyen and Woflgang Stahl — Institute of Physical Chemistry, RWTH Aachen University, Germany
Proton tunneling is an important class of large amplitude motions, which appears in some secondary amines like dimethyl amine (DMA) and ethyl methyl amine (EMA). This causes splittings of the rotational lines of 2646.0 MHz and 1981.0 MHz for DMA and EMA, respectively.
In the case of diethyl amine, CH3CH2NHCH2CH3, we found a barrier to inversion of 18.31 kJ/mol from the separation between the lowest symmetric and antisymmetric inversion energy level of E = 760.77062(20) MHz for all c type transitions. b type lines show only narrow splittings due to Coriolis coupling. Moreover, due to the nuclear spin of I = 1 of the 14N nucleus hyperfine splittings arise. The inversion splittings of diethyl amine were described with molecular parameters using the programs spfit and spcat by Pickett instead of reporting the splitting of each single rotational transition as in previous work.
Methyl tert-butyl amine, (CH3)3CNHCH3, is a further secondary amine we investigated. Quantum chemical studies showed that the most stable conformer has a CS symmetry and proton tunneling is possible. A preliminary assignment with Pickett’s spfit code including overall rotational and tunneling effects was carried out. The separation between the two inversion energy levels is 698.903(99) MHz for c type lines in this case. Centrifugal distortion and 14N hyperfine coupling effects have not yet been considered.