Rotation-vibration hyperfine structure

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 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. 

The characterization of the X and a state levels of homonuelear and heteronuclear alkali dimer molecules formed by decay of the upper levels formed by photoassociation is discussed next. Resonance-enhanced multiphoton ionization is shown to be a powerful technique for establishing the population of vibrational levels formed in the X and a states near the dissociation limit. A new ion depletion technique for observing rotational and hyperfine structure as well for these levels near dissoeiation is also discussed. To reach lower levels, especially in the ground X state, it is useful to select specific photoassociation approaches such as double minimum excited-state potentials, resonant coupling of two (or more) excited state potentials, and stimulated Raman transfer from levels near dissociation to low levels (e.g., the collisionally stable V = 0,J = 0 level). 

The rotational, vibrational, fine-structure, and hyperfine-structure constants for the NH ion, derived from the high-resolution IR autodetachment spectra, are given above the electron affinity of the NH molecule is given on p. 38. 

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 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 ... 

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. 

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. 

Cooke et al. [04Coo] have recorded the electric nuclear quadrupole and magnetic spin-rotation hyperfine structures of the 1-0, 2-1, and 3-2 pure rotational transitions in the X electronic and o = 0 vibrational ground states using laser ablation MWFT techniques in the frequency region between 7 and 22 GHz. The uncertainty of the line positions is about lkHz. The following parameters have been determined ... 

The sub-Doppler nature of double resonance with single mode c.w. lasers has been used to resolve hyperfine structure in an infrared-optical study of NH2 (Amano et. al. 1982). A fluorescence cell was placed inside the cavity of a CO2/N2O laser and between the poles of a 15" electromagnet capable of fields up to 22 kG. A dye laser beam was introduced into the cell through a ZnSe mirror, and excited NH2 fluorescence through transitions to levels of the V2 = 9 or 10 states. At magnetic fields which Zeeman tuned into resonance vibration-rotation transitions within the excited state the population transfer changed... 

Fig. 2.21 Hyperfine and super-hyperfine structures of a rotational-vibrational transition in SP6, showing the molecular transitions and cross-over signals (a) experimental spectrum (b) calculated spectrum [223]...

S.D. Rosner, R.A. Holt, T.D. GaUy, Measurement of the zero-field hyperfine structure of a single vibration-rotation level of Na2 by a laser-fluorescence molecular-beam resonance. Phys. Rev. Lett. 35, 785 (1975)... 

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