摘要:

Single crystal E.S.R. studies of Cu(II) and Ag(II) dialkyldiselenocarbamates, diluted in the corresponding Ni(II) complexes, are reported. A method has been developed which removes the necessity to measure the spectra on the same single crystal and in three mutually orthogonal planes. Equations have been derived for the resonance fields and the transition probabilities, taking into account the full spin hamiltonian and without assuming coinciding tensor axes. Applying these equations thegtensor and the metal hyperfine and quadrupole coupling tensors are obtained in high precision. In contrast to the situation in the corresponding dithiocarbamates, it was found for all diselenocarbamates studied that the axes of thegand metal hyperfine tensor do not coincide and that the relative orientation depends on the central metal ion and on the molecular symmetry. The highestgvalue was always found in the molecular plane, whereas in the dithiocarbamates the highest value is found perpendicular to the molecular plane. The spectra reveal the presence of two sets of two equivalent Se atoms, so that the molecule has inversion symmetry. Especially from the measured77Se hyperfine splittings it could be concluded that the built in guest molecule accepts the structure of the host crystal. Also measurements are reported on powders, glasses and liquid solutions. Evidence has been obtained that in the latter two media thegand metal hyperfine principal axes coincide.

ISSN:0026-8976    

DOI:10.1080/00268977500100841

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

The spin hamiltonian parameters of Cu(II) dialkyldiselenocarbamates, diluted in the corresponding Ni(II) complexes, have been calculated from the results of extended Hückel Molecular Orbital calculations and compared with the experimentally obtained values (Part I). Without the 4d functions of selenium, all calculated hyperfine couplings (those of copper as well as those of selenium, hence nine principal values) and two of the principalgvalues are found in very good agreement with the experimental ones. The third principalgvalue can be brought into agreement with the experimental value if the 4d functions of selenium are taken into account. In doing this also the rotation of the principal axes ofgtensor relative to those of the copper hyperfine tensor can be understood. The results of the extended Hückel calculations show that the hyperfine couplings of the selenium atoms are determined almost completely by the molecular orbital of the unpaired electron. This enabled us to calculate the selenium part of this molecular orbital directly from the experimental splittings. From a comparison between the selenium hyperfine splittings in corresponding copper and silver compounds it could be concluded that the delocalization of the unpaired electron to the selenium atoms is much larger in the silver than in the copper compounds.

ISSN:0026-8976    

DOI:10.1080/00268977500100851

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

Measurements of the MCD spectra of Ni2+in KMgF3and KZnF3have confirmed and extended previous assignments of spin-orbit structure based on similarities of vibrational patterns. The measurements also reveal the presence of a1A1g(1G) state which interacts strongly with the3T1gb(3P) state. The MCD spectra of the tetragonal crystals K3Ni2F7and K2NiF4have been measured for the transitions3A2g→3T1ga,1Eg. The spectrum of K3Ni2F7is characterized by the appearance of electric dipole zero phonon lines, consistent with theC4vsite symmetry of the Ni2+in the paramagnetic phase. An analysis of the MCD spectrum allows a positive assignment of six of the seven states (from3T1gaand1Eg) to which transitions are allowed by symmetry in the axial spectrum. A complete tetragonal crystal-field analysis has been made which shows that the distortion is an axial compression of the fluoride octahedron. The absorption spectrum of K2NiF4shows much less vibrational structure, but the MCD spectrum allows a definitive assignment of six states (from3T1gaand1Eg) througha2uvibrations in the usual vibronic mechanism. False origins based oneuphonons have not been identified. The tetragonal field is larger than for K3Ni2F7and corresponds to an axial compression, in agreement with the known crystal structure.

ISSN:0026-8976    

DOI:10.1080/00268977500100861

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

Dilute gas viscosity data may be inverted directly to give the intermolecular potential energy function if the well depth is known. The consequences of using different values of the well depth are studied, and it is concluded that the correct value may be distinguished by using second virial coefficient data.

ISSN:0026-8976    

DOI:10.1080/00268977500100871

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

The problem of the exchange interaction between two2Pions is studied. As a first step, from the true electrostatic hamiltonian, the symmetry and the energy of each term arising from the interaction between two orbitally degenerate ions are determined. As a second step, a phenomenological model, invariant with respect to a unitary transformation between the atomic orbital basis functions leading to the same terms as the true electrostatic perturbation, is proposed.

ISSN:0026-8976    

DOI:10.1080/00268977500100881

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

The thermodynamic perturbation theory of Stell, Rasaiah and Narang is generalized to the case of multi-component Stockmayer fluids. The effects of polarization by the permanent dipoles is included to first order and the perturbation series is summed approximately to all orders in the dipole moments by means of two Padé approximants. The two-body and triplet terms in the expansion have been evaluated by Monte Carlo integration for a specific choice of the reference Lennard-Jones mixture and the results are used to study systematically the effect of dipolar interactions on excess thermodynamic properties. The utility of a one-fluid theory based on the van der Waals model is investigated and it is shown that the approach is useful for obtaining semi-quantitative information on mixtures of weakly polar fluids. The special case of mixtures of hydrogen chloride and xenon is considered and it is shown that the potential model used is inadequate to account for the large deviations from ideality which are observed for this system.

ISSN:0026-8976    

DOI:10.1080/00268977500100891

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

Intensity perturbations in forbidden radiative transitions due to cubic anharmonic mixing involving the inducing mode and a totally symmetric progression-forming mode are discussed. It is shown that such mixing will lead to deviations from mirror symmetry of the absorption and fluorescence structure because the destructive-constructive interference pattern which prevails in absorption is different to that in emission. This analysis is applied to intensities in the 2600 Å system of benzene. Moderate cubic coupling energies (ca.10 cm-1) have marked effects on intensity distributionseven when the interacting levels are 200 cm-1apart. The splitting of the progressions 10n612and 1n0621into two sub-progressions (l=0, 2) is linearly dependent on the extent of vibronic excitation in thea1gmodev1. These effects are amenable to experimental detection.

ISSN:0026-8976    

DOI:10.1080/00268977500100901

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

A sum rule treatment using Hall's equivalent orbitals has been applied to the valence orbital ionization energies of mono-, di- and trimethylamine up to about 40 eV assuming Koopman's theorem. Excellent agreement is obtained between theory and experiment in partial and total energy sums. A similar treatment usingp-type localized orbitals previously proposed by the authors is also applied to ionization energies below about 18 eV for the methyl amines. In these sum rule treatments we use both the vertical ionization energies obtained from He (I) photoelectron spectra measured here and the higher ionization energies deduced from the He (II) photoelectron spectra published by Pottset al.The complete sets of valence orbital ionization energies of the methyl amines have thus been identified by sum rule considerations in photoelectron spectroscopy. We show that the character of the corresponding MO's may be inferred from the sum rule. The orbital orderings and characters of the methyl amines have also been studied by CNDO/2 and MINDO/2 methods.

ISSN:0026-8976    

DOI:10.1080/00268977500100911

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

63Cu N.M.R. transitions of divalent copper ions have been detected for the first time in Zeeman perturbed quadrupole levels in the exchange coupled pair of copper acetate monohydrate at the temperatures 20 to 60 K. The electric quadrupole coupling tensor at the Cu nuclear site at 20 K was determined to bee2Qq= 117 ± 2 MHz and η = 2·8 ± 0·1 per cent from the anisotropy of resonance frequency by means of third-order approximation in Zeeman interaction. The temperature dependence of the spin-lattice relaxation rate along thex-axis is proportional to the triplet spin population, which is compatible with the model that the relaxation is brought about by the fluctuation of hyperfine coupling via triplet spins. The second-order perturbation of the static part of the hyperfine coupling results in indirect nuclear spin coupling in the exchange coupled pair. Splitting into quartet with equal spacing of 9·6 gauss due to theI-Icoupling was observed along thez-axis.

ISSN:0026-8976    

DOI:10.1080/00268977500100921

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

We compute the radiative phosphorescence lifetime of caffeine using CNDO/S wavefunctions. The importance ofnπ*, πσ* and σπ* singlet and triplet states is considered. The calculated values are in good agreement with experimental determinations. The role played by two-electron terms is briefly discussed.

ISSN:0026-8976    

DOI:10.1080/00268977500100931

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor