First results for ethylphosphine, CH3CH2PH2, from an effective rotational Hamiltonian for two-rotor systems with symmetric and asymmetric internal rotors (like ethanol)

Groner, Peter

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https://hdl.handle.net/2142/100608 Copy

Description

Title

First results for ethylphosphine, CH3CH2PH2, from an effective rotational Hamiltonian for two-rotor systems with symmetric and asymmetric internal rotors (like ethanol)

Author(s)

Groner, Peter

Issue Date

2018-06-19

Keyword(s)

Large amplitude motions, internal rotation

Abstract

Spectra of molecules with a 3-fold internal rotor become much more interesting in the presence of another largeamplitude motion (LAM) that leads to tunneling between equivalent asymmetric forms which may also tunnel to a different conformer. An effective rotational Hamiltonian has been derived for such a system of which ethanol, CH3CH2OH, is a typical example a . For isolated vibrational states of molecules with two symmetric rotors with sufficiently ”high” barriers, the ERHAM codeb works well. Modifications were explored to find out whether ERHAM can be coaxed to treat ethanoltype systems, using ”ancient” unpublished microwave data from vibrational ground and excited states of ethylphospine, CH3CH2PH2, as test data. For gauche ethylphosphine, the splitting between the a-type Coriolis-coupled ground states is 5.215(6) MHz whereas it is 229.9(2) MHz in the ν24 state (PH2 torsion). The tunneling energy coefficients 01 for the methyl internal rotation are -0.63(2) MHz and 2.93(5) MHz (sign undeterminable), respectively. These results look promising; however, up to now, sets of assigned frequencies had to be omitted from fits to experimental uncertainty of 25 kHz: (a) for the ground state, all c-type transitions J4,J−3 - J3,J−3 (41 < J < 48) for systematic large deviations (reason unknown); (b) for the ν24 state, half of the quartets of the J3,J−2 - J2,J−2 series (28 < J < 32) because of interactions with a state of the trans conformer) and some of the Ka = 1, 2 low-J transitions (incorrect assignments or unknown reasons). Analyses of data for the ν23 (CH3 torsion) and ν22 (CCP deformation) states are in progress.

Publisher

International Symposium on Molecular Spectroscopy

Type of Resource

text

Language

eng

Permalink

http://hdl.handle.net/2142/100608

DOI

10.15278/isms.2018.TK09

Copyright and License Information

Copyright 2018 Peter Groner

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