Centrifugal distortions constants

The centrifugal distortion constant depends on the stifthess of the bond and it is not surprising that it can be related to the vibration wavenumber co, in the harmonic approximation (see Section 1.3.6), by... 

The vibrational dependence of the centrifugal distortion constant is too small to concern us further. 

Evidence for a significant contribution from the ionic form [BX] + - -Y in a gas-phase complex B- XY was first deduced from the spectroscopic constants of H3N- -ClF, as obtained by analysis of its rotational spectrum [63]. In particular, the value ka = 34.3 N m 1 of the intermolecular stretching force constant (obtained from the centrifugal distortion constant Dj in the man-... 

Values were also reported for the rotational constants, centrifugal distortion constants, and the chlorine nuclear quadrupole coupling constants of the three isotopic species F C1 02, F CF 02, and i F CF 0 0. The molecular dipole moment was found to be 1.722 0.03 D. 

Over the last years we have explored several advanced techniques for high-resolution rotational coherence spectroscopy (RCS [1]) in order to study the structures of molecules and clusters in the gas phase [2]. We have provided spectroscopic examples demonstrating (i) mass-selectivity (Fig. 1, [3]), (ii) that the rotational constants of the ground and electronic excited states can be obtained independently with high precision (lO MO"5, [4]), (iii) that the transition dipole moment alignment, (iv) centrifugal distortion constants, and (v) information on the polarizability tensor can be obtained (Fig.l, [5]). Here we review results pertaining to points (i), (ii), (iv) and (v) [2,3,5],... 

The method of fs DFWM spectroscopy and our theoretical model for the spectral simulation is discussed in our second contribution in this volume. The experimental setup has been detailed in a former publication [5], Here, we would like to highlight some special features of this technique with emphasis on the possibility to obtain, besides the rotational constants, centrifugal distortion constants (CDs) and information on the polarizability tensor (PT). 

The conclusion is that if the spectrum can be analysed in terms of equations (3)—(7), then the force constants can be determined. The bond length re can be determined from the equilibrium rotational constant Bc then the quadratic force constant /3 can be determined either from the harmonic wavenumber cubic force constant /3 can be determined from aB and finally the quartic force constant /4 can be determined from x. It is necessary to determine the force constants in this order since in each case we depend upon already knowing the preceding constants of lower order. The values of re,f2,f3, and /4 calculated in this way for a number of diatomic molecules are shown in Table 2. 

Figure 1-9. Variation of the vibrational band origin Ai q, effective rotational constant B, and centrifugal distortion constant D with the size N of the cluster He -C02. Circles and dots indicate the experimental and theoretical results, respectively. The upper panel also includes for comparison the value of for clusters of He with OCS and N20. The inset in the middle panel shows the results calculated in an extended range of helium atoms in the cluster. The dashed lines indicate the nanodroplet results of Miller and collaborators 367...

It is now possible to determine precise rotational spectra for hydrogen bonded molecules of moderate size and with even very small stabilization energies. Rotational constants, centrifugal distortion constants, electric dipole moments and nuclear hyperfine interactions have been measured for a considerable number of dimers using various microwave and molecular beam techniques. 

The centrifugal distortion constant Drn, is the result of the second-order vibrational contributions ... 

Table 8.16. Molecular parameters for H35 Cl determined from the electric resonance spectra. All parameters are in kHz except for the electric dipole moment, n(v), which is in Debye units (D). The rotational and centrifugal distortion constants were obtained by Rank, Rao and Wiggins [102], S]2 is the spin-spin interaction constant, equal to [gig2ii2N(no/47t)/(2J + 3)(2J - 1)](R 3)vj...

In addition several centrifugal distortion constants were listed these become significant as J values increase and, as we shall see, are very important in the case of the OH radical. We will defer our discussion of centrifugal distortion until we deal with OH. 

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