Centrifugal distortion analysis of the rotational spectrum of aziridine: Comparison of different Hamiltonians |
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Authors: | RA Motiyenko EA Alekseev J-C Guillemin |
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Institution: | a Laboratoire de Physique des Lasers, Atomes et Molécules, UMR CNRS 8523, Université de Lille I, 59655 Villeneuve d’Ascq Cedex, France b Sciences Chimiques de Rennes, Ecole Nationale Supérieure de Chimie de Rennes-CNRS, 35700 Rennes, France |
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Abstract: | Previous measurements of rotational spectrum of aziridine up to 1.85 THz have been supplemented by new data in 225-660 GHz frequency range. A total of 1465 transitions (915 of them are newly assigned ones) with maximum values of J = 59 and Kc = 50 were fit to a standard Watson Hamiltonian using the S- and A-reductions and the representations Ir and IIIr. Although aziridine is an asymmetric oblate top, the combination (A, IIIr) gives the worst results. From the point of view of the convergence of the Hamiltonian, the best results are obtained with the combination (S, IIIr). It is explained that the failure of the combination (A, IIIr) is due to the large value of the parameter σ=(2C-A-B)/(A-B) which makes some sextic centrifugal distortion constants much too large impeding the convergence of the Hamiltonian. It is also shown that the calculation of the centrifugal distortion constants from a force field is sometimes an ill-conditioned operation. Finally, the use of a non-reduced Hamiltonian (with six quartic centrifugal distortion constants) was successful in the particular case thanks to the method of predicate observations. |
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Keywords: | Aziridine Centrifugal distortion Reduction Representation Ab initio Rotational Hamiltonian |
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