Atomic properties quadrupole moments

Recent work improved earlier results and considered the effects of electron correlation and vibrational averaging [278], Especially the effects of intra-atomic correlation, which were seen to be significant for rare-gas pairs, have been studied for H2-He pairs and compared with interatomic electron correlation the contributions due to intra- and interatomic correlation are of opposite sign. Localized SCF orbitals were used again to reduce the basis set superposition error. Special care was taken to assure that the supermolecular wavefunctions separate correctly for R —> oo into a product of correlated H2 wavefunctions, and a correlated as well as polarized He wavefunction. At the Cl level, all atomic and molecular properties (polarizability, quadrupole moment) were found to be in agreement with the accurate values to within 1%. Various extensions of the basis set have resulted in variations of the induced dipole moment of less than 1% [279], Table 4.5 shows the computed dipole components, px, pz, as functions of separation, R, orientation (0°, 90°, 45° relative to the internuclear axis), and three vibrational spacings r, in 10-6 a.u. of dipole strength [279]. 

Differences in CC bond lengths of the aromatic moiety, which are less than 0.025 A are indeed small if compared to distances of 1.48 A and 1.33 A characterising C(sp2)-C(sp2) single and C(sp2)=C(sp2) double bonds, respectively, as usually pointed out by X-ray researchers. However, they are quite significant for many properties which critically depend on interatomic distances like e.g. molecular quadrupole moments, electric field gradients, spin-spin coupling constants of directly bonded atoms etc. A... 

Empirical, semiempirical, and ab initio methods have been used extensively to calculate molecular descriptors. These molecular property descriptors help capture important characteristics of compounds such as bioavailability and receptor affinity. Descriptors such as octanol-water partition coefficient (log P), HOMO/LUMO energies, hammett a, total energy, heats of formation, ionization potential, atomic charges, electron densities, dipole/quadrupole moments, volume, and polar surface area are common examples. For an excellent review of physicochemical descriptors, the reader is directed to the following reference. ... 

Fig. 6.8. A comparison of the C-C bond and atomic properties of the carbon atoms in the pentadienyl cation with the corresponding fragment (as indicated by the numbering of the atoms) in the benzenium ion, protonated benzene. The bond properties compared are bond order n, bond ellipticity e, and the Laplacian at the bond critical point, The atomic properties compared are the net charges on the carbons g(C) and their quadrupole moments Q,.(C). Also given are the differences in energy of the carbon atoms, A (C) = FfClCCeH. ] - ElQCCjH ...

Table 2.1 List of molecules studied with four-component methods. The fourth column lists quantities, which have been investigated primary data P = (total electronic energies (E), orbital energies e,-, population analyses PA), ionization energies IE, election affinities EA, atomization energies A, spectroscopic data S = (equilibrium distance re, dissociation energy De, frequencies/wave numbers coe, bond angles 0), electric properties E = (dipole moment fx, quadrupole moment 0, dipole polarizability a, infrared intensities I, excited states ES, electric field gradients EFG, energetics of reaction R.

Chromium has the atomic number 24. Of the 13 known isotopes (mass numbers 45-57), four are stable, giving chromium the relative atomic mass 51.9961 = 12.0000). Table 1 lists the properties of some isotopes. Cr may be used for NMR spectroscopy however, its relative receptivity (8.62 x 10 , H = 1.00), quadrupole moment (4.1 x 10 ° m ), and low resonance frequency (16.956MHz, = 300MHz) pose experimental difficulties. Radioactive Cr is used in medical tracer studies. 

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