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Line Assignments and Global Analysis of the Tunneling-Rotational Microwave Absorption Spectrum of Dimethyl Methylphosphonate



N Ohashi, J Pyka, G Y. Golubiatnikow, Jon T. Hougen, R D. Suenram, Francis J. Lovas, A Lesarri, Y Kawashima


Line assignments were carried out for about 600 Fourier transform microwave transitions for dimethyl methylphosphonate involving levels of all six symmetry species in the G18 molecular symmetry group appropriate for three large-amplitude motions and covering J and K values of 2 less then or equal to} J less then or equal to 6 and 0 less then or equal to}K less then or equal to) 3. The assignments are based on combination-difference loops, variations in line shape for different symmetry species caused by the small internal-rotor splitting patterns of the third, high-barrier methyl top, and agreement with theoretically expected positions. A global fit of 609 lines to a phenomenological tunneling-rotational Hamiltonian with 65 constants was performed, yielding a standard deviation of 0.0072 MHz, which is close to the experimental measurement uncertainty. Tunneling splittings for the two lowest barrier methyl-group internal rotation motions were determined indirectly to be about 4900 and 34000 MHz, respectively. The much smaller tunneling splitting for the methyoxy interchange motion was determined (with some assumptions) to be 3.3 MHz.
Journal of Molecular Spectroscopy
No. 1


global fit, group theory, internal rotation, large amplitude motion, multi-dimensional tunneling, tunneling splittings


Ohashi, N. , Pyka, J. , Golubiatnikow, G. , Hougen, J. , Suenram, R. , Lovas, F. , Lesarri, A. and Kawashima, Y. (2003), Line Assignments and Global Analysis of the Tunneling-Rotational Microwave Absorption Spectrum of Dimethyl Methylphosphonate, Journal of Molecular Spectroscopy (Accessed May 28, 2024)


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Created February 28, 2003, Updated October 12, 2021