摘要:

This paper opens a series of articles devoted to the theoretical calculation and physical interpretation of the band shapes in the infra-red and Raman spectra of H-bonded liquids on the basis of the fluctuation model of hydrogen bonding. In the present introductory article general features of the fluctuation model are discussed and the fluctuations of H-bond configurations are classified as dynamical and statistical ones. It is shown that in liquids such as water or alcohols the statistical fluctuations play a dominant role, i.e. the band broadening originates from disorder in equilibrium positions and orientations of the molecules in liquid. This idea does not yet permit us, however, to make the direct calculations of the spectral band shape on the basis of structural data. A semi-empirical approach is proposed instead which allows us to calculate in the frames of the fluctuation model the band shapes in the infra-red and Raman spectra of numerous water complexes with organic bases and of pure H2O and D2O starting from spectra of HOD in similar complexes. The comparison of calculated and experimental spectra will be used in the following papers to justify the physical model.

ISSN:0026-8976    

DOI:10.1080/00268977500103161

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

To describe the distortion perturbations of the water molecules in solutions the quantum-mechanical method of partial oscillators has been developed. This method allows one to separate in a simple manner two types of influences on vibrations of OH oscillators, viz. the intermolecular perturbations resulting in the different strengths of hydrogen bonds and intramolecular coupling between stretching vibrations. Here the coupling is treated quite strictly, whereas the intermolecular perturbations are introduced phenomenologically. The calculation of the distribution of distortions among molecules in liquid H2O and D2O induced by non-equivalency of the two hydrogen bonds of the water molecule has been made on the basis of the method developed, and the parameters of the mean statistical molecule have been found from the experimental spectrum of HOD. The depolarization ratios of vibrations in Raman spectra of the mean statistical molecules H2O and D2O have been computed as an illustration of the possibilities of the proposed calculation method. All the estimates show that the stretching oscillators of H2O and D2O molecules are significantly coupled in spite of the great distortion of the symmetry of water molecules in the liquid state.

ISSN:0026-8976    

DOI:10.1080/00268977500103171

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

On the basis of the fluctuation hypothesis of hydrogen bonding analytical formulae are obtained for the band shape in the infra-red and Raman spectra of stretching vibrations of H2O molecules with only one OH group involved in H-bonding (so-called complexes of the type 1-1 [1]). The statistical distribution of stretching frequencies ωOHaffected by H-bonds of different strengths is derived from the spectrum of HOD molecules in a similar complex using empirical correlation between the half-width of the band and the shift of its maximum relative to monomeric frequency. The coupling of intramolecular vibrations has been taken into account by means of the method of partial oscillators developed in [3], and the frequencies and intensities have been calculated in vibrational spectra of a continuum of water molecules differently perturbed by H-bonding. The series of computations are performed with varying values of basic parameters of the model in order to establish their influence on the spectra. The results of calculations demonstrate the broadening of the line of ‘free’ OH oscillators, the additional divergence of maxima positions, and redistribution of intensities between ‘free’ and H-bonded oscillators produced by their coupling. A specific behaviour of the depolarization ratio across the Raman bands follows also from calculations. Some of the predictions are in good agreement with experimental data while others are still waiting for experimental verification.

ISSN:0026-8976    

DOI:10.1080/00268977500103181

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

Thermodynamic properties of liquid mixtures in which strong anisotropic intermolecular forces exist are studied using the Padé approximant method used by Stellet al.for pure fluids. Equations for the third-order perturbation term are derived for a general intermolecular potential of multipolar type. Using a mixture of Lennard-Jones molecules as the reference system, the effects of adding point dipole, quadrupole and anisotropic overlap potentials are calculated. Numerical results are presented (at low pressures) for the effect of these forces on the excess functions, and on the vapor-liquid equilibrium curves. These anisotropic forces lead to positive deviations from Raoult's law. Strong polar and quadrupolar forces may cause liquid-liquid immiscibility to occur. Numerical calculations are presented to illustrate such behaviour; these systems have upper critical solution points.

ISSN:0026-8976    

DOI:10.1080/00268977500103191

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

The magnetic circular dichroism (MCD) spectra of the1B2u←1A1gtransition of benzene in nitrogen and argon matrices at 20 K have been measured in order to obtain a spectrum devoid of hot bands and complicating rotational structure. The spectrum is dominated by three progressions ofBterms, two of positive sign and one of negative. One positive progression and the negative one can be definitely assigned to thee2gmodesv6andv9respectively, whilst the other positive progression may be thee2gmodev8. This is in marked contrast with the absorption spectra of the same matrices which reveal only a single progression built uponv6. The MCD spectra are nicely accounted for in terms of a magnetic mixing between the1B1uand1B2ustates, the electric dipole intensity arising from the mixing in of a1E1ustate viae2gvibrational modes.

ISSN:0026-8976    

DOI:10.1080/00268977500103201

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

Die gestaltungsmässige Abhängigkeit der hyperfeinen Kupplungavon einem an der Position β eines freien Radikals anliegenden Kerns kann immer in der Form einer Serie von Fourier im Bezug auf den Torsionswinkel ϑ ausgedrückt werden. Die bekannte Formela=B0+B2cos2ϑ drückt nur die minimale charakteristische Ausdehnung (m.k.A.) für die Radikale vom Typ π aus, bei denen die geminalen Substituenten von dem schon erwähnten Kern identisch sind. Wenn diese letzte Bedingung nicht erfüllt ist, ist die Symmetrie durch die Umkehrung von ϑ zerstört und ein gerader Sinusterm erscheint in der m.k.A., was zu einer Verschiebung ϑ in der schon erwähnten Formel führt. Wenn die Lappen der ungepaarten Orbitale unsymmetrisch sind, wie es in den Radikalen vom Typ σ der Fall ist, kehrt die Periode der Funktionavon π zu 2π und ungerade Schwingungen in der m.k.A. erscheinen, welche dann bis zu fünf Termen gehen kann. Die Methode der kleinsten Quadrate, auf Serien von theoretischen Kupplungen angewandt, kann die Unterscheidung der wichtigsten Terme ermöglichen, deren physisiche Interpretation dann gesucht werden kann. Es wird auch gezeigt, dass die Koeffizienten der verschiedenen m.k.A. im allgemeinen keine linearischen Funktionen der Hauptspindichte TANO sind, deren durchschmittlicher Wert an den Gestaltungen gerechnet ist.

ISSN:0026-8976    

DOI:10.1080/00268977500103211

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

Compton profiles are derived fromab initioSCF-MO wavefunctions calculated for cyclopropane, propene, aziridine, ethanimine, ethenamine, oxirane, acetaldehyde and formamide using Dunning's gaussian orbital basis. Good agreement with the experimental profile is found for formamide. The differences between the profiles for the cyclic and acyclic isomers are only slightly larger than the experimental accuracy that can presently be achieved. The cyclic compounds have slightly broader profiles and there are no significant differences arising from strain. Comparison with profiles derived from localized orbital contributions indicate that the localized orbital approach is essentially valid for these systems.

ISSN:0026-8976    

DOI:10.1080/00268977500103221

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

Transient signals in the fluorescence intensity induced by microwaves can be used to acquire quantitative information on the molecular rates of populating and depopulating of the lowest triplet state of organic molecules. This method seems especially promising when the molecule emits no detectable phosphorescence.

ISSN:0026-8976    

DOI:10.1080/00268977500103231

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

The Hubbard relations for linear molecules in the cases of the extended diffusion model (EDM) and Ivanov's theory are derived. TheM-diffusion variant of the EDM leads to an unphysical result as the dielectric and Raman correlation times approach infinity and it is suggested thatM-diffusion is not a realistic model. TheJ-diffusion is almost the same as for spherical molecules. When the reduced angular momentum correlation time, τJ*, is very much less than unity both EDM and Ivanov theory give a relation similar to the friction model [2], i.e. the original Hubbard relations [14] with the coefficient 6-1, instead of 2-1as obtained by O'Reilly [3]. For τJ* > 1 the various versions of Hubbard's relations are different enough to be distinguished experimentally.

ISSN:0026-8976    

DOI:10.1080/00268977500103241

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

Die π-Elektronen-Beiträge zu den H,H-Kopplungskonstanten von Vinylverbindungen wurden mittels der Finiten Störungstheorie in INDO- und INDO/σ-Näherung berechnet. Die Einzentrum-Core-Matrixelemente der INDO/σ-Methode werden angegeben. Die berechneten π-Beiträge zu Kopplungskonstanten über zwei bis über fünf Bindungen stimmen gut mit den Ergebnissen von π-Elektronen-MO-Theorien überein.

ISSN:0026-8976    

DOI:10.1080/00268977500103251

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor