The Experts below are selected from a list of 9831 Experts worldwide ranked by ideXlab platform

John M. Brown - One of the best experts on this subject based on the ideXlab platform.

Christian Hill - One of the best experts on this subject based on the ideXlab platform.

James K.g. Watson - One of the best experts on this subject based on the ideXlab platform.

  • calculated octic Centrifugal Distortion coefficients of non linear molecules
    Journal of Molecular Structure, 2006
    Co-Authors: James K.g. Watson
    Abstract:

    The equilibrium octic Centrifugal Distortion coefficients of a molecule are coefficients of terms of the type H˜08 in the expansion of the effective Hamiltonian. They depend on the quartic potential constants kklmn′ for the vibrational modes that have non-zero inertial derivatives, and therefore give information on these constants additional to that given by the other terms that depend on the quartic potential, H˜24 and H˜40. The present work describes the calculation of these H˜08 terms from a given potential by perturbation theory, using a computer program that calculates the coefficients in the successive contact transformations. Results are presented for the SO2, ClO2, O3, and H2O molecules.

  • The vibrational dependence of quartic Centrifugal Distortion
    Journal of Molecular Structure, 2005
    Co-Authors: James K.g. Watson
    Abstract:

    Abstract The dependence of the quartic Centrifugal Distortion coefficients of a molecule on the vibrational quantum number vk is of type H ˜ 24 in the expansion of the effective Hamiltonian. It gives information on the quartic potential constants of the type k ′ k k l m and is therefore additional to that provided by the anharmonicity constants xkl, which depend only on the quartic potential constants of the type k ′ k k l l . The present work describes the calculation of these H ˜ 24 terms from a given potential by perturbation theory, using a computer program which calculates the coefficients in the successive contact transformations. Results are presented, in terms of directional Centrifugal Distortion constants, for the SO2, ClO2, O3, and H2O molecules. Good agreement with observed coefficients is obtained for SO2 and ClO2. For O3, the strong rotational resonance between the (100) and (001) states complicates the comparison, and the transformation to the effective Hamiltonian used empirically requires further study. For H2O, poor agreement is obtained for the (010) level because of quasilinear behaviour. The effects of the resonance between (100) and (001) are less severe than for O3, and the agreement with the observed is somewhat better.

  • The vibrational dependence of quartic Centrifugal Distortion
    Journal of Molecular Structure, 2005
    Co-Authors: James K.g. Watson
    Abstract:

    The dependence of the quartic Centrifugal Distortion coefficients of a molecule on the vibrational quantum number vk is of type H24 in the expansion of the effective Hamiltonian. It gives information on the quartic potential constants of the type k'kklm and is therefore additional to that provided by the anharmonicity constants xkl, which depend only on the quartic potential constants of the type k'kkll. The present work describes the calculation of these H24 terms from a given potential by perturbation theory, using a computer program which calculates the coefficients in the successive contact transformations. Results are presented, in terms of directional Centrifugal Distortion constants, for the SO2, ClO2, O3, and H2O molecules. Good agreement with observed coefficients is obtained for SO2 and ClO2. For O3, the strong rotational resonance between the (100) and (001) states complicates the comparison, and the transformation to the effective Hamiltonian used empirically requires further study. For H2O, poor agreement is obtained for the (010) level because of quasilinear behaviour. The effects of the resonance between (100) and (001) are less severe than for O3, and the agreement with the observed is somewhat better.Peer reviewed: NoNRC publication: Ye

Jean Demaison - One of the best experts on this subject based on the ideXlab platform.

  • Centrifugal Distortion analysis of the rotational spectrum of aziridine: Comparison of different Hamiltonians
    Journal of Molecular Spectroscopy, 2010
    Co-Authors: Roman A. Motiyenko, Laurent Margulès, E. A. Alekseev, Jean-claude Guillemin, Jean Demaison
    Abstract:

    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 = ( 2 C - 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.

  • The Rotational Spectrum of Propene: Internal Rotation Analysis and ab Initio and Experimental Centrifugal Distortion Constants
    Journal of Molecular Spectroscopy, 1994
    Co-Authors: G. Wlodarczak, Jean Demaison, N. Heineking, Attila G. Császár
    Abstract:

    Abstract Following the measurement of the rotational spectrum of propene in the microwave and millimeterwave regions, internal rotation and Centrifugal Distortion analysis is performed. A scaled quantum mechanical force field is calculated, and the theoretical Centrifugal Distortion constants, calculated from this force field, are compared to the experimental ones.

  • Centrifugal Distortion Analysis of an Asymmetric Top: The Case of Imidazole
    Journal of Molecular Spectroscopy, 1993
    Co-Authors: Jean Demaison, M. Leguennec, Georges Wlodarczak, B.p. Vaneijck
    Abstract:

    Abstract Three aspects of the Centrifugal Distortion analysis are reviewed: (i) prediction of the quartic Centrifugal Distortion constants from an ab initio force field, (ii) empirical relations between the quartic constants T αα and the corresponding rotational constants B α , and (iii) order of magnitude of the planarity defect for planar molecules. As an illustration the rotational spectrum of the planar molecule imidazole is analyzed.

B.d. Green - One of the best experts on this subject based on the ideXlab platform.

  • The effects of Centrifugal Distortion on the infrared radiative transition probabilities of NO(X2II)
    Journal of Quantitative Spectroscopy and Radiative Transfer, 1996
    Co-Authors: K.w. Holtzclaw, W.t. Rawlins, B.d. Green
    Abstract:

    Abstract State-to-state and thermally averaged Einstein A -coefficients have been computed for the fundamental and first three overtone sequences of the NO(X2II-X2II) system with the aim of examining the effects of Centrifugal Distortion on the high-J transitions that occur as a result of upper atmospheric chemistry. The Einstein coefficients were calculated using an experimentally derived dipole moment function of Rawlins et al (manuscipt in preparation), and the ab initio dipole moment functions of Langhoff et al [Chem. Phys. Lett. 223, 416 (1994)] and de Vivie and Peyerimhoff [J. Chem. Phys. 89, 3027 (1988)], for J′ ranging up to 139.5. The state-specific Einstein coefficients show that, regardless of dipole moment function employed, Centrifugal Distortion has a relatively small effect on the Δv = 1 sequence which is manifest primarily as a reduction in the high-J R-branch intensities. However, the effect on the overtone rotational intensities is larger and results in enhanced R-branch intensities and reduced P-branch intensities relative to those calculated neglecting Centrifugal Distortion. For example, in the first overtone system for J′ ≈ 80.5, v′ = 2–14, the ratio of R- to P-branch Einstein coefficients is larger by about 1.7 than the R P ratio predicted in the absence of Centrifugal Distortion.