Sextic distortion constant

Occasionally it is found necessary to include a sextic distortion constant H) as well, and the term 1) ... 

The sextic distortion constants were fitted as global constants across all states. 

Infrared measurements yield the vibrational frequencies associated with the various normal vibrational modes, and these data, including isotopic frequency data, can be used to evaluate the force constant matrix F = Since these calculations are often iU conditioned and also since there are usually more force constants than vibrational frequency data, both infrared data and the microwave distortion constant data are often combined to help characterize the force constant matrix. Some examples are given in Table XIV. It may be noted that the F or sextic distortion constants depend on the cubic potential constants, and these data have been employed to obtain information on these anharmonic potential constants. 

Watson has shown that of the six quaitic distortion constants (7) only five combinations are generally determinable from the spectra (one exception is nearly spherical tops such as SO2F2). Furthermore, only seven combinations of the ten sextic constants ([Pg.7]

The excited-state sextic centrifugal distortion constants were constrained to their ground state values. Reference... 

Tables in the present chapter contain in their upper part data on the spin-rotation interaction constants e q (q = Inertial axes a, b, c) and In their lower part data on the rotational constants A, B, and C. Methods of measurement, references, and remarks are the same for either constant. The quartic (A, 8 and A, 5) and sextic (O, (p) centrifugal distortion constants listed In the first table (for the electronic ground state of PHg) are defined by the A-reduced form (asymmetric reduction) of the respective Hamiltonian for spin-rotation Interaction and rotation [1 to 3]. Abbreviations used in the tables are MW for microwave absorption, EL AB for electronic absorption, LMR for laser magnetic resonance, FIR for far IR, IMF for Intermodulated fluorescence.

Similar data were previously reported [3]. For the sextic centrifugal distortion constants Hj, Hjk. Hk, hj, hjK, and hK[4], see the original papers [2, 3]. 

Sextic centrifugal distortion constants constrained to the ground state values. 

Higher order terms for rotation (sextic centrifugal distortion constants Hk, Hkn. H k, Hn. k, hpjK. h vi plus the eigth-power term Lk) and spin-rotation coupling (quartic centrifugal... 

Rotational and Centrifugal Distortion Constants. The rotational constants of gaseous NH2 were obtained by fitting the rovibrational bands of the high-resolution IR spectrum to a Watson-type S-reduced Hamiltonian. The results in cm for the ground state of the ion are Ao = 23.0508 0.0019, Bo = 13.0684 0.0015, Cq = 8.11463 0.00048, Dj = 0.001082 0.000022, Djk=-0.00381 0.00012, Dk = 0.02065 0.00013, Di =-0.000492 0.000014, and 2= -0.0000461 0.0000054. The corresponding values for the v l and the Va = 1 states and the estimated equilibrium rotational constants of the ground state are also listed. The analysis was restricted to quartic distortion terms, because the inclusion of sextic terms did not result in a better fit of the bands. The Hamiltonian used does not include the effects of the rotational interactions which are noticeable in some bands [2]. Rotational constants... 

Figure 7 Plot of log Hj against the function of log B for various C3 symmetric tops B is the rotational constant, Hj is one sextic centrifugal distortion constant. Reproduced with permission from Demaison J, Bocquet R, Chen WD, Papousek D, Boucher D and Burger H (1994) The far-infrared spectrum of methylchloride determination and order of magnitude of the sextic centrifugal distortion constants in symmetric tops. Journal of Molecular Spectroscopy 166 147.

Bg = equilibrium rotational constant = rotational constant in the Vj vibrational mode = rotational constant D, d= quartic centrifugal distortion constants Go v) = vibrational term value when the energy levels are referred to the ground state as zero H, h = sextic distorsion constants = Boltzmann... 

Unreduced constants quartic and sextic centrifugal distortion constants according to Wilson [36Wil]... 

The sextic equilibrium centrifugal distortion constants of N2H and N2D, Hj = 50 and 35 mHz, were estimated in an ab initio (CEPA-1) study [2]. 

The Watson representation of the Hamiltonian for the near-symmetric asymmetric top was also used in order to obtain centrifugal distortion constants from FT-IR spectra [5 to 7], FT-MW spectra [8], and a continuous MW spectrum [2]. The resulting quartic constants are given in Table 9 see the cited papers for the values of the sextic and higher terms. 

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