Vibrational hyperfine structures

This type of background correction assumes that the background absorption has a continuum nature within the spectral bandwidth of the monochromator. This is not the case when the background absorption arises from molecular bands, which have a rotation-vibration hyperfine structure. These can arise from radicals produced by a dissociation of the solvent (OH, SO2, SO3, N2, CN, etc.) but also from molecular oxides (MO). As such contributions occur particularly with the complex... 

The results of research on the NMR spectra of elements with different isotopic composition have been reported. (95) The particular interest of these investigations lies in the possibility of applying perturbation theory to account for the contribution of vibrational states to the shielding of nuclei. (96, 97) In addition, the measurement of nuclear g factors of isotopic pairs, with great accuracy, is required for evaluating small hyperfine structure anomalies. (39,98)... 

Much of the beauty of high-resolution molecular spectroscopy arises from the patterns formed by the fine and hyperfine structure associated with a given transition. All of this structure involves angular momentum in some sense or other and its interpretation depends heavily on the proper description of such motion. Angular momentum theory is very powerful and general. It applies equally to rotations in spin or vibrational coordinate space as to rotations in ordinary three-dimensional space. 

In this book, which is concerned predominantly with rotational transitions and their fine and hyperfine structure, we will have only a peripheral interest in the details of vibrational structure. Similarly we will not usually be concerned directly with electronic transitions, except in double resonance studies. Nevertheless it is important to see the broader picture, in order to understand better the detailed structure. 

Figure 8.29. Electric resonance spectrum of CsF in strong fields, showing resonance from molecules in five different vibrational levels (v = 0 to 4). The hyperfine structure resulting from nuclear-molecular interactions is not resolved [50].

Figure 11.50. Energy level diagram (not to scale) showing the nuclear hyperfine structure of the HD+ 22,1 and 22,0 vibration-rotation levels (labelled with the G and G2 quantum numbers described in the text). The infrared transitions which give rise to the six lines shown in figure 11.49 (a) are shown on the left-hand side of the figure, and the four observed microwave transitions are shown on the right-hand side.

Molecules or radicals have different electronic energy levels ( S, 2S, 2n,...), which have a vibrational fine structure (v = 0,1,2,3,...) and the latter again have a rotational hyperfine structure (/ = 0,1,2,3,...). The total energy of a state is then given by ... 

In the present discussion we shall not consider the special problems introduced by large amplitude vibrations such as methyl torsions (see H. Dreizler, this volume) or ring puckering (see W. J. Lafferty, this volume). Also, it is assumed that perturbations, such as nuclear hyperfine structure, have been corrected. 

Thus, by measuring the intermolecular vibrations of a WBC, ultimately with resolution of the rotational, tunnelling and hyperfine structure, the most sensitive measure of the IPS is accessed directly. The difficulty of measuring these VRT spectra is the fact that they he nearly exclusively at THz frequencies. As expected, the stiffer the interaction, the higher in frequency these modes are found. In general, the total 0.3-30 THz interval must be accessed, although for the softest or heaviest species the modes rarely lie above 10-15 THz. 

The collision-assisted predissociation in iodine B O + state merits a detailed discussion. It is well known that B state is weakly coupled to the dissociative A 1m state by rotational and hyperfine-structure terms in the molecular Hamiltonian. The natural predissociation rate strongly depends on the vibrational quantum number (pronounced maxima for o=5 and u = 25, a minimum for u= 15), this dependence being due to a variation of the Franck-Condon factor. " The predissociation rate is enhanced by collisions. In absence of a detailed theoretical treatment of the colhsion-assisted 12 predissociation, one can suppose that the asymmetric perturbation (breakdown of the orbital symmetry) in the collisional complex affects electronic and rotational wavefimctions but does not change the nuclear geometry. 

There have been calculations on smaller systems (the ethynyl radical) by a hybrid DFT + Molecular Dynamics scheme. The vibrationally averaged motions modify the hyperfine structure of the radical and are shown to agree much better with the experimental data than do the optimized vacuum geometry results." It would be fascinating to extend these methods to some of the radicals discussed here where vibrations at the radical site seem to be present. In cases where the theoretical and experimental results are not too different, perhaps it is time to work together on alternative models which embody the best parts of the experimental results in concert with the very useful trends indicated by the theoretical results. Perhaps some compromise here might actually produce models which show even better agreement with the experimental results." ... 

A number of halogenomethanes have been subjected to other forms of molecular spectroscopy. High-resolution Stark spectra of several transitions of the V3 band of CH3F have been studied by means of a CO2 laser measurements of the hyperfine structure on certain rotational transitions in CH2F2 have been made using a molecular beam maser spectrometer the millimetre-wave spectrum of ground-state CDCla and the microwave spectrum of CD3I in excited vibrational states have also been observed. 

Theoretical analysis of the vibrational spectra of FgCO, CI2CO, and BraCO and the electronic spectra of (CN)2CO has been attempted the hyperfine structure on certain rotational transitions in F2CO has been observed using a molecular beam maser spectrometer, ... 

Leung et al. [06Leu] have measured electronic ground state rotational transitions and their nuclear electric quadrupole and magnetic hyperfine structures in the n = 0 and o = 1 vibrational states using MWFT spectroscopy. From the vibrational dependence of the fitted spectroscopic parameters their equilibrium values could be determined. 

Evans and Gerry [OOEva] have measured the hyperfine structure of the 7=1-0 transitions in the = 0 and u = 1 vibrational states using MWFT techniques, with the following results ... 

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