Atomic quadrupole moment complexes

All carbene complexes were characterized by their h, C NMR, and IR spectra. In the C NMR spectra the resonances of the earbene C-atoms are found at very low field between 334.0 ppm (2f) and 348.3 ppm (2g). Most of the signals are broadened or occur twice. This phenomenon is due to the quadrupole moment of manganese and hindered rotation around the 0-C(earbene) bond and O-Si bond as often described [6]. The IR spectra show the eharaeteristic absorption bands of the diazo group (v = 2100 cm ) and the carbonyl ligands (v = 1850-2000 cm ). 

If a more complex adsorbate is being studied, (N2, CO2, water, etc.) the orientation dependence should be added to the model. For the linear Nj molecule, e.g., a three-site L-J pair potential is typically used [17]. The three sites correspond to the N atoms and the center of mass. The interaction between the atomic sites is taken to be a L-J 12-6 potential function, and partial charges are placed on the three sites in the molecule to reproduce the known quadrupole moment. 

If the nucleus of the acceptor atom M has a nuclear spin quantum number greater than -j, the nucleus has an electric quadrupole moment as well as a magnetic dipole moment. The quadrupole interacts with any electric field gradient at the nucleus and, in combination with the molecular motion of the complex, this can provide an important mechanism of relaxation of the M nucleus. At relaxation rates that are slow compared with Jp M, spin multiplets are observable in the spectra of M and P. As the relaxation rate increases, the multiplets broaden, but the line separations may still be used to derive 7p Mwith good accuracy. At faster relaxation rates the multiplet components of M and P coalesce into a single broadened line, and at high relaxation rates, the phosphorus resonance becomes sharp and the M resonance may become so broad as to be unobservable. 

Thus, observations of spin multiplets due to a quadrupolar nucleus are most often successful when the atom M is attached to several identical ligands, because the electric field gradient at the nucleus is thereby made small. As the magnitude of the quadrupole moment becomes large (e.g., for Co), a symmetrical complex becomes virtually a necessary condition for the observation of coupling. 

Anisotropy in the Rg-HX system (Rg = rare gas, X = F, Cl) is largely determined by the R induction term, involving the dipole polarizability of the rare gas atom and the dipole and quadrupole moments of the hydride molecule [80]. The corresponding dispersion term, involving frequency-dependent polarizabilities, gives further stabilization to the H-bonding in these complexes. 

X2-Y complex. The r dependence can be easily obtained for X2-Y complexes (where Y is an atom of noble gas in the ground state) in (3.1.9) if only the leading quadrupole-induced dipole interaction is taken into account. In this case, the equilibrium distances (/fg) of the complexes are comparable with the size of X2 molecules. As a result, the modelling of a molecule in the form of a point, for which the interacting molecules are considered as not having the size, can not be applied and should be modified to take the size of a molecule into account. For this purpose, each molecule of a complex is considered as two effective point atoms without any interactions between them. The position of these atoms coincides with those of the nuclei of the molecule. The tensor of the total quadrupole moment of the effective atoms is the same as that of the molecule. For the diatomic homonuclear molecule the quadmpole moments of the effective atoms are equal to each other. Thus, the dipole moment of the complex is a function of intra- and intermolecular separations and relative orientation of the complex components. As a result, in the framework... 

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