摘要:

Colloidal silver and gold particles have been prepared by reduction of aqueous metal salt solutions in inverse microemulsions. The sols are characterized by absorption spectroscopy and electron microscopy. Ultrasound treatment during reduction results in a narrower size distribution of the colloidal particles, as evidenced by a narrower absorption band. Photochemical silver and gold sol formation, without the addition of a reducing agent, has been observed for inverse microemulsions of metal salt solutions in a medium consisting of dodecyl-heptaethyleneglycol-ether and hexane. The particle sizes determined from electron microscopy have been used as input parameters for the simulation of absorption spectra, based on the electromagnetic theory of localized surface plasmon excitation. For the gold sols a quantitative agreement between experimental and simulated spectra is obtained. With the silver colloids, the observed red-shift of the absorption maximum points to the presence of an ionic layer on the surface of the particles. When this layer is included in the theoretical model, good agreement with the experiment is achieved.

ISSN:0026-8976    

DOI:10.1080/00268979000100011

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The first magneto-optical study of the4A2g→2T2gabsorption,2Eg→4A2gand2T2g→2T1g,2Egluminescences of MoCl3-6in Cs2NaYCl6, as well as the absorption spectrum of the spin-allowed4T2gand4T1gligand field states, are reported. Magneto-optical methods have allowed difficulties in a previous assignment to be resolved. Coupling of almost all electronic origins to α1g,t2uand botht1uMoCl3-6internal modes, as well ast1ulattice modes, is established, uniquely, from the sign of the magnetic circular dichroism and magnetic circular polarization of luminescence spectra. In addition, coupling to at1uinternal mode of the host YCl3-6unit is observed. Moderate coupling to theegJahn-Teller mode occurs for the2T2g(U′),2T1g(U′) and2Eg(U′) origins, particularly the former, but is very weak or absent for the2T2g(E″) and2T1g(E′) origins. A comparison of the relative dipole strengths induced byt1uandt2uvibrations, as well as the sign of the MCPL for the2Eg→4A2gtransition, are consistent with the intensity for the4A2g→2Eg,2T1g,2T2gtransitions being borrowed primarily from the4T2gstate via spin-orbit coupling. The observed2T1gand2T2gspin-orbit splittings of 102 and 75cm-1, respectively, are reduced by approximately one third from those calculated, and this reduction is attributed to a Jahn-Teller effect.

ISSN:0026-8976    

DOI:10.1080/00268979000100021

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The ground state rotational spectrum of gauche-N2F4has been investigated between 8 and 200 GHz, including quantum states up toJ= 74 andKa= 39. Quadrupole coupling hyperfine structures were analysed to give χaa= 2·246(12) MHz and χcc= -1·792(5) MHz. The hypothetical (eQ= 0) centre frequencies were fitted using a rigid-rotor hamiltonian including centrifugal-distortion terms up to eighth degree in (J, K). The rotational constants areA= 5576·1995(1) MHz,B= 3189·432 77(8) MHz andC= 2813·169 55(8) MHz. The electric dipole moment along thecaxis was determined from field shifts of magic-doublet components to be μe= 0·256(4) D.

ISSN:0026-8976    

DOI:10.1080/00268979000100031

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The theory of nutation N.M.R. for a quadrupolar nucleus with spin quantumI= 5/2 is presented in an exact, analytical way. It is shown that the nutation spectrum is described by 9 different frequencies each dependent on the orientation of the quadrupole tensor relative to the external field. The frequencies are calculated from the eigenvalues of a 6th-degree secular equation that is reduced to 2 secular equations of order 3. This reduction is obtained by a transformation of bases. An extension of the nutation experiment,xx¯-nutation, is compared with the standard technique. The theoretical spectra are compared with experimental27Al spectra of NH4Al(SO4)2· 12H2O and zeolite NaA.

ISSN:0026-8976    

DOI:10.1080/00268979000100041

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Vector correlations, vibrational fragment pair correlations and population distributions in OH(D) photofragments generatedviatwo photon, vibrationally mediated photodissociation of HOOH(D) at selected wavelengths near 750 nm, have been determined using polarized, Doppler-resolved LIF spectroscopy. These measurements, together with a knowledge of the direct,singlephoton dissociation dynamics at comparable supplied energies,

ISSN:0026-8976    

DOI:10.1080/00268979000100051

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

A calculation of the van der Waals contribution to the physisorption energy is performed for molecules interacting with small metallic spheres. The induction contribution is introduced by using the first field gradient susceptibilities of the sphere at zero frequency. In order to illustrate the non local effects as well as the importance of the curvature of the metal particle on the magnitude of the physisorption energy, we present numerical results for typical systems (HF, HCl on Ag, Cu and Al).

ISSN:0026-8976    

DOI:10.1080/00268979000100061

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Point symmetry is essentially a discrete concept, whereas molecular structures and their conformational changes display continuous features, even within semi-classical models. Using the formalism of fuzzy-set theory, we propose a continuous extension of the point-symmetry concept for quasi-symmetric structures. For each pointkof the reduced nuclear configuration (metric) spaceMof the set of all molecular systems having a specified stoichiometry, and for an energy criterion ϵ suggested by the statics or the dynamics of the systems, we define membership functions μi(k, ϵ) which generate fuzzy subsetsSi(ϵ) of the metric spaceM. These fuzzy subsets are used to obtain a continuous extension of the symmetry point groups of formal, classical, nuclear configurations.

ISSN:0026-8976    

DOI:10.1080/00268979000100071

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Molecular dynamics simulation of molten Li2CO3and Na2CO3has been performed. The parameters of the pair potentials have been obtained from MO calculation by using a 3–21 G basis set. Comparison of structure of Li2CO3with Na2CO3reveals that the difference in predominant position of the cations with respect to the neighbouring anion may be explained in terms of the difference in the ionic radii of the cations. Some dynamic properties such as self-diffusion and rotational motion of the anion are also discussed in relation to the structures.

ISSN:0026-8976    

DOI:10.1080/00268979000100081

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Ab initiocalculations, which describe the topography of the potential energy surface of OH(A2Σ+) + CO(X1Σ+) and its interaction with the lowest lying surfaces, OH(X2Π) + CO(X1Σ+), have been used to produce analytical functions for studying the mechanism of electronic quenching with classical mechanics. We distinguish four separate regions on the potential energy surface where quenching occurs, according to the orientation of CO with respect to OH. With the assumption that trapped trajectories lead to quenching with probability equal to one, the contribution of each region to the total quenching cross sections is estimated. The calculated total cross sections are in good agreement with the experimental values. The anisotropy of the potential function justifies the decrease of the quenching cross sections with increase of the initial rotational level of OH. Because of the complex formation the cross sections are also decreased by increasing the collision temperature.

ISSN:0026-8976    

DOI:10.1080/00268979000100091

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Potential energy surfaces of twelve electronic states of ZrH2are constructed using a complete active space self-consistent field method (CASSCF) followed by mult-reference singles + doubles configuration interaction (MRSDCI) calculations. The Zr(3F) ground state of zirconium atom has to surmount a barrier of 11 kcal/mole for insertion into H2. The excited Zr(1D) state inserts into H2almost spontaneously. The excited Zr(5F) atom forms a weak complex with H2and subsequently has to surmount a large barrier for insertion into H2. Three possible nearly-degenerate bent electronic states are found for ZrH2(1A1,3B1and3A1). The1A1ground state of ZrH2was found to be 26 kcal/mole more stable compared to Zr(3F) + H2. Mulliken population analyses reveal considerable 4d5s5phybridization of the metal atom in the Zr-H bonds. The dipole moments of bent low-lying electronic states reveal that the ZrH bonds are ionic with Zr+H-polarity. The effects of ten-component 4f-type functions are also studied on the various electronic states of ZrH2.

ISSN:0026-8976    

DOI:10.1080/00268979000100101

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor