Rotational hyperfine structure

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 ... 

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 ... 

Molecules are beginning to play a key role in another area of fundamental interest, namely in testing the temporal and spatial variation of the fundamental constants. Molecular vibration, rotation, hyperfine structure, and other features offer combinations of the fundamental constants that are not available with atoms. 

Puzzarini, C., Cazzoli, G., Harding, M. E., Vazquez, J., and Gauss, J. (2009). A new experimental absolute nuclear magnetic shielding scale for oxygen based on the rotational hyperfine structure of H2 0. J. Chem. Phys., 131, 234304. 

Figure Bl.4.9. Top rotation-tunnelling hyperfine structure in one of the flipping inodes of (020)3 near 3 THz. The small splittings seen in the Q-branch transitions are induced by the bound-free hydrogen atom tiiimelling by the water monomers. Bottom the low-frequency torsional mode structure of the water duner spectrum, includmg a detailed comparison of theoretical calculations of the dynamics with those observed experimentally [ ]. The symbols next to the arrows depict the parallel (A k= 0) versus perpendicular (A = 1) nature of the selection rules in the pseudorotation manifold.

Quadrupole coupling constants for molecules are usually determined from the hyperfine structure of pure rotational spectra or from electric-beam and magnetic-beam resonance spectroscopies. Nuclear magnetic resonance, electron spin resonance and Mossbauer spectroscopies are also routes to the property. There is a large amount of experimental data for and halogen-substituted molecules. Less data is available for deuterium because the nuclear quadrupole is small. 

The hyperfine structure of the R(127) rotational line in the 11-5 band of molecular iodine at X = 6328 A could be resolved by Lamb dip spectroscopy with a halfwidth of 4.5 MHz, and the influ-enie of isotopic substition and has been studied 38, 338a)k)... 

EPR studies showed that RsSi radicals (R = Me, Et, i-Pr and t-Bu), obtained by hydrogen abstraction from the parent silanes by photogenerated t-BuO radicals, add to Ceo to form the corresponding adducts [29], The spectra of MesSi- and t-Bus Si-adducts have hyperfine structure due to 9 and 27 equivalent protons, respectively, at 27 °C suggesting free rotation of Si—C bonds on the EPR time scale. On the other hand, the middle members of the series, EtsSi-and z-Pr3 Si-adduct radicals, showed a unexpected hyperfine manifold which has been accommodated with free rotation about the Si—Ceo and frozen rotation about the Si—R bonds on the EPR time scale. 

The microwave spectra of 1//-benzotriazole and its N-D isotopomer have been studied in a heated cell. The molecule is planar. Due to the quadrupole coupling effects of the N nuclei, no hyperfine structures are observed. The dipole moment of benzotriazole obtained by microwave is 4.3 D, which is in agreement with the value determined in solution. The rotational spectrum is also assigned <93JSP(161)136>. 

Abstract. Investigation of P,T-parity nonconservation (PNC) phenomena is of fundamental importance for physics. Experiments to search for PNC effects have been performed on TIE and YbF molecules and are in progress for PbO and PbF molecules. For interpretation of molecular PNC experiments it is necessary to calculate those needed molecular properties which cannot be measured. In particular, electronic densities in heavy-atom cores are required for interpretation of the measured data in terms of the P,T-odd properties of elementary particles or P,T-odd interactions between them. Reliable calculations of the core properties (PNC effect, hyperfine structure etc., which are described by the operators heavily concentrated in atomic cores or on nuclei) usually require accurate accounting for both relativistic and correlation effects in heavy-atom systems. In this paper, some basic aspects of the experimental search for PNC effects in heavy-atom molecules and the computational methods used in their electronic structure calculations are discussed. The latter include the generalized relativistic effective core potential (GRECP) approach and the methods of nonvariational and variational one-center restoration of correct shapes of four-component spinors in atomic cores after a two-component GRECP calculation of a molecule. Their efficiency is illustrated with calculations of parameters of the effective P,T-odd spin-rotational Hamiltonians in the molecules PbF, HgF, YbF, BaF, TIF, and PbO. 

The phenomenon of NQR is the origin of hyperfine structure in microwave rotational spectra (see Section 2.04.2.1), as well as in electron and nuclear paramagnetic resonance. 

Through the interaction described above, the nuclear spin momentum is coupled to the rotation of the molecule with the result that the rotational levels of the molecule are split into a number of components, giving an associated hyperfine structure to the spectra. 

Fine structure and hyperfine structure of rotational levels... 

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