摘要:

We have investigated the EPR spectral lines of the photo-excited triplet state of pyrene-d-10 both in a fluorene single crystal and an ethanol glass matrix. In the crystal we have measured the width, shape and saturation parameters, λ′,aandB1/2u, of the ΔM= 1 lines from both sites in the cleavage plane,Y-Z, at 193 K and along the principal directions,X, Y, Z, between 143 K and 300 K. In the glass the same parameters have been measured for the six resonances of the absorption derivative at 77 K. We have used a general deconvolution procedure to extract the unresolved inhomogeneous and homogeneous broadenings, ΔBGand ΔBL≡ 1/γT2, and the spin-lattice relaxation rate,T1-1, from λ′,aandB1/2ufor the different types of resonances. The use of Fourier-series expansions permits optimal utilization of the data and resolution of the terms of different symmetries for these quantities. The application of the method of moments, using assumed spin densities, permits the demonstration that the main contribution to the constant term of ΔBG, but only a small part of its anisotropy, originates from the intramolecular hyperfine interactions. AsT2andT1are of the same order of magnitude, we have assumed the same mechanism, i.e. modulation of the fine-structure tensorD, for both relaxation effects. A first-order semi-classical treatment leads to partial agreement between the main features of the calculated and observed orientation dependences if one assumes strongly anisotropic librations coupled to large modulations ofD. This is consistent with the maximal libration amplitudes estimated from the differences between theDtensors measured in the crystal and in the glass. Variations with temperature are attributed to a competition between the increase of modulation amplitudes and decrease of correlation time with heating.

ISSN:0026-8976    

DOI:10.1080/00268977800102341

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

The decomposition of non-adiabatic wavefunctions of diatomic molecules into electronic and vibrational functions is discussed and the properties of the resulting non-adiabatic pseudo-potentials are investigated. It is shown that the vibrational part of the wavefunction is nodeless and the corresponding pseudo-potential differs significantly from the adiabatic potential for all vibrationally excited (v≠ 0) states. The differences take the form of potential barriers positioned at the nodes of the adiabatic vibrational function. It is argued that this excludes the possibility of defining anab initionon-adiabatic potential that could have a practical significance.

ISSN:0026-8976    

DOI:10.1080/00268977800102351

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

The detailed group structure of the independent-particle hamiltonian is derived in terms of interior and exterior products of groups describing various types of symmetry operations which commute with the hamiltonian. Modifications of this group due to external fields are examined, as are the concepts of the equivalence of particles. Simplifications due to isomorphisms and homomorphisms are outlined. Applications involving representations within this construction are examined.

ISSN:0026-8976    

DOI:10.1080/00268977800102361

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

The effect of internal ligand modes on the radiationless relaxation in metal complexes is considered. The theoretical model of the process is formulated within the framework of a dynamic coupling mechanism. The non-radiative rate constant is given as a product of an electronic and a vibrational factor, and it is concluded that it is the electronic factor that is rate-determining.

ISSN:0026-8976    

DOI:10.1080/00268977800102371

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

We analyse a simple model for the correlation functions of the hard-sphere solid. The result is in agreement with the parametrization introduced by Weis and Kincaid and Weis. By transforming this result we show singularities in the structure factor which result from the long-range part ofg(r).

ISSN:0026-8976    

DOI:10.1080/00268977800102381

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

We introduce a model hard-sphere solid with correlation functions in excellent agreement with hard-sphere solid correlation functions calculated from simulations. The model solid is of independently distributed Gaussian particles centred at the points of a face-centred cubic lattice. We generalize the model to any lattice and use it to calculate contributions to the internal energy due to long-ranged potentials.

ISSN:0026-8976    

DOI:10.1080/00268977800102391

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

Our non-empirical pseudo-potential method is tested on the molecules ScH3, TiH3F, MnO4-, Zn(CH3)2and Pd(CO)4. The calculations are performed with the PSIBMOL algorithm, described in paper I (Molec. Phys., 1977,33,159) at the independent particle restricted Hartree-Fock level with minimal and double-zeta basis sets of Slater orbitals expanded in gaussian functions. The agreement between pseudo-potential and all-electron calculations for these molecules is as good as for non-transition element compounds as concerns valence molecular orbital energies and expectation values of various one-electron operators. The general conclusion of this series (papers I, II and III) is that our non-empirical pseudo-potential method can now be used as a routine tool to predict efficiently the ground-state valence electronic properties of molecules containing any atom of the Periodic Table as far as relativistic effects remain unimportant.

ISSN:0026-8976    

DOI:10.1080/00268977800102401

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

Ab initioquantum-mechanical calculations on the triatomic ions HNO+and NOH+in their lowest two electronic states are reported, which approximate complete configuration interaction results in a double-zeta plus polarization quality basis. Relative energies of key points on the potential energy surfaces are determined as a function of wavefunction accuracy and used to give best estimated values. Ground-state HNO+has an equilibrium geometry withrNH= 1·063 Å,rNO= 1·127 Å, < HNO = 125·9°, and an energy 54 kJ/mol lower than isomeric NOH+, whose ground-state equilibrium geometry isrOH= 1·006 Å,rNO= 1·180 Å and < NOH = 116·4°. The lowest barrier to isomerization on the ground-state surface is 247 kJ/mol. The HNO+dissociation energy to H + NO+is 147 kJ/mol. The NOH+dissociation energy to the same dissociation limit is 88 kJ/mol. Vertical excitation from the ground-state equilibrium HNO+molecule is at an energy of 1·78 eV, in good agreement with the 7200 Å (1·73 eV) absorption system reported by Herzberg. In NOH+the equivalent excitation is at 1·39 eV. Excited state HNO+has a linear equilibrium geometry withrNH= 1·040 Å,rNO= 1·130 Å, and is 71 kJ/mol below excited state NOH+whose equilibrium geometry is also linear, withrOH= 0·998 Å,rNO= 1·171 Å. In the excited state the lowest barrier to isomerization is 251 kJ/mol. Rotational constants are reported.

ISSN:0026-8976    

DOI:10.1080/00268977800102411

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

A simple analytical model of rotational effects in thermal decomposition is developed. The model describes the non-equilibrium population distribution of the reactant, as a function of the average vibrational energy lost per deactivating collision. The corresponding non-equilibrium rate constant is evaluated, and the results are compared to two previous models.

ISSN:0026-8976    

DOI:10.1080/00268977800102421

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

A report is given on ENDOR investigations of the structure of radicals in X-irradiated tri-glycine sulphate single crystals at 77 K and 300 K. Two non-equivalent radicals of the type NH3+-ĊH-COO-which originate at sites on the glycine molecules gly II and gly III were identified. Their hyperfine coupling parameeters differ by a maximum of 1 MHz at room temperature. The radicals have non-equivalent β-protons indicating strongly hindered rotation of the amino group. INDO calculations were also performed. The radicals were found to be non-planar. The proton deviates from the nodal plane of the π-orbital by about 10°. The positions of the hydrogen atoms of the amino groups were found to agree with the corresponding hydrogen bonds in the non-irradiated crystals.

ISSN:0026-8976    

DOI:10.1080/00268977800102431

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor