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 Title: COMPETITION BETWEEN TWO LARGE-AMPLITUDE MOTION MODELS: NEW HYBRID HAMILTONIAN VERSUS OLD PURE-TUNNELING HAMILTONIAN Author(s): Kleiner, Isabelle Contributor(s): Hougen, Jon T. Subject(s): Large amplitude motions, internal rotation Abstract: In this talk we report on our progress in trying to make the hybrid Hamiltonian competitive with the pure-tunneling_x000d_ Hamiltonian for treating large-amplitude motions in methylamine. A treatment using the pure-tunneling model has _x000d_ the advantages of: (i) requiring relatively little computer time, (ii) working with relatively uncorrelated fitting_x000d_ parameters, and (iii) yielding in the vast majority of cases fits to experimental measurement accuracy. These _x000d_ advantages are all illustrated in the work published this past year on a gigantic $v_{t}$ = 1 data set for the torsional_x000d_ fundamental band in methyl aminefootnote{I. Gulaczyk, M. Kreglewski, V.-M. Horneman, J. Mol. Spectrosc., in Press_x000d_ (2017).}. A treatment using the hybrid model has the advantages of: (i) being able to carry out a global fit _x000d_ involving both $v_{t}$ = 0 and $v_{t}$ = 1 energy levels and (ii) working with fitting parameters that have a clearer _x000d_ physical interpretation. Unfortunately, a treatment using the hybrid model has the great disadvantage _x000d_ of requiring a highly correlated set of fitting parameters to achieve reasonable fitting accuracy, which _x000d_ complicates the search for a good set of molecular fitting parameters and a fit to experimental accuracy. _x000d_ At the time of writing this abstract, we have been able to carry out a fit with J up to 15 that includes all _x000d_ available infrared data in the $v_{t}$ = 1-0 torsional fundamental band, all ground-state microwave data with _x000d_ K up to 10 and J up to 15, and about a hundred microwave lines within the $v_{t}$ = 1 torsional state, _x000d_ achieving weighted root-mean-square (rms) deviations of about 1.4, 2.8, and 4.2 for these three categories of data._x000d_ We will give an update of this situation at the meeting._x000d_ Issue Date: 6/20/2017 Publisher: International Symposium on Molecular Spectroscopy Citation Info: APS Genre: CONFERENCE PAPER/PRESENTATION Type: Text Language: English URI: http://hdl.handle.net/2142/96829 DOI: 10.15278/isms.2017.TI08 Date Available in IDEALS: 2017-07-27
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