6, rotational constant characteristic

When optical rotation data are expressed in this standard way, the specific rotation, (o-Jq, is a physical constant characteristic of a given optically active... 

Due to the characteristics of the technique, comparisons of -parameters in microwave spectroscopy are not meaningful within 0.01 A6, particularly if one or several atoms are close to a principal axis of rotation. When restructures are determined from three rotational constants for a species with more than three degrees of freedom, no estimate is possible of the significance of the results. 

For a particular compound the observed rotation depends on the concentration of the compound, the path length of the sample tube, and the wavelength of the light that is used. Often the yellow light produced by a sodium lamp, called the sodium D line (wavelength = 589 run), is used. The specific rotation, a constant characteristic of each... 

The rate of deposition is calculated for a spherical, cylindrical, or rotating disc collector the dimensionless rate of deposition was found to be a function of a single dimensionless group B, involving the rate constant, characteristic velocity, diffusion coefficient, and (except in the case of a disc) the collector size. 

The SAPT potential for the He-C02 complex was also used in the calculations of the rovibrational spectra of the He -CC clusters 366. High resolution experimental data were also reported in this paper. Comparison of the theoretical and experimental effective rotational constants B and other spectroscopic characteristics as functions of the cluster size N is shown on Figure 1-9. Again, the agreement between the theory and experiment is impressive showing that theory can describe with trust spectroscopic characteristics of small clusters He -CO This especially true for the effective rotational constant and the frequency shift of the C02 vibration due to the solvation by the helium atoms. One may note in passing that the clusters HeA,-C02 with the number of helium atoms N around 20 do not exhibit all the properties of the C02 molecule in the first solvation shell of the (quantum) liquid helium at very low temperatures. 

The values of p and T can now be used for the statistical mechanical calculations. In order to calculate the rotational characteristic temperature t with Eq. (20), use the literature value for the rotational constant Bo = 0.037315 cm [or calculate Bo from the internuclear distance in the molecule, rg = 0.2667 nm, with Eqs. (17) to (19)]. From the literature value of the molecular vibrational frequency in the gas phase, Tg = 213.3 cm , calculate the vibrational characteristic temperature vu, with Eq. (22). From the phonon dispersion data in Table 1, calculate the 12 vibrational characteristic temperatures , -. 

When optical rotation data arc expressed in this standard way, the specific rotation, lain, is a physical constant characteristic oTa given opticall> active compound- For example, the (e > lactic acid Uiat we saw in Section 9.1 has al > +3.82 , and (—> Iactic acid has loin -S-Blf - Some additional examples are listed in Table 9 l. 

In a real molecule of course, the PES cannot be changed at will. Nevertheless, mixings are well known in spectroscopy and can be observed in quantities like rotational constants, intensities or any other characteristic feature of an absorption or emission spectrum. The external parameter is usually one of the rotational quantum numbers, J or K. The energy of a rovibrational state is approximately given by an expression for the symmetric top molecule, i.e.. 

Systematic and extensive attention has been paid to the high resolution electronic (vacuum ultraviolet) absorption spectra of X. .. x " and X. .. molecules, where X, Y are noble gas atoms. Measurements were performed in the 58-126 nm region with a 6.65 m vacuum spectrograph. The individual band systems were identified and very accurate characteristics were obtained for the ground states (the potential depths, number of stable vibrational levels, rotational constants and interatomic separations). 

Iy(t) can be calculated. Since we are interested in comparing simulated decays with observed ones, all the simulated decays presented were convoluted with a temporal response function characteristic of that of our experimental apparatus.42 In addition, all simulations pertain to the anthracene molecule. Thus, all rotational constants used, (B + C) and A - + C), were near 0.415... 

The results obtained from the measurement of the observed angle of rotation, ttobs/ are generally expressed in terms of specific rotation [a].The sign and magnitude of [a] are dependent on the specific molecule and are determined by complex features of molecular structure and conformation they cannot be easily explained or predicted. The specific rotation is a physical constant characteristic of a substance. The relationship of [a] to aobs is as follows ... 

According to the values of the predicted electric dipole moment components and rotational constants listed in Table 1, the rotational spectra of most of the threonine conformers are dominated by pa-type, R-branch transitions forming groups of lines with characteristic patterns which appear at frequency intervals equivalent to B -f C. Wide frequency scans with low power polarization conditions were conducted to search for such rotational transitions of conformers with relatively large pa- Several sets of R-branch lines corresponding to five different rotamers are labeled L, M, N, O, and P. Spectral searches, conducted to detect other sets of pa-type R-branch transitions, using high microwave power for polarization, were unsuccessful. Therefore, wide frequency scans were carried out to identify pu- and pc-type transitions. Finally, two more rotamers labeled Q and R were identified. 

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