摘要:

The Lorentz half-widths of collision-broadened lines in the rotation-vibration bands of diatomic molecules vary with line number |m| in thePandRbranches. The observed variation of half-width for lines in the 0 → 1 and 0 → 2 bands of CO and HCl are interpreted in terms of a simple fitting procedure. One dominant source of line broadening is assumed to consist of diabatic hard collisions involving transitions from each rotational level to all higher rotational levels; the effectiveness of this process, which varies from line to line, is described in terms of an empirically adjusted collision cross section, a maximum collision parameter related to independently measured molecular properties, and upon the availability of the required energy and angular momentum in molecular collisions. The second source of line broadening, assumed to be the same for all lines, includes all other types of collisions and is represented by a single empirically adjusted cross section. The simple fitting procedure is applied successfully to self-broadening of CO lines and to foreign-gas broadening of CO and HCl; for HCl self-broadening an additional cross section for resonant-dipole processes must be included. Possible applications of the fitting procedure to HBr, HF, and CO2are discussed. The simple procedure presented represents an approximation that may prove useful pending the development of readily applicable complete theories based on first principles.

ISSN:0026-8976    

DOI:10.1080/00268977100100761

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

The absorption and circular dichroism spectra of (-)d-1,12-dimethyl-benzo[c]phenanthrene-5-acetic acid are reported, together with the polarized excitation and fluorescence spectra of the parent hydrocarbon, [4]-helicene. The transition energies of 1,12-dimethyl-[4]-helicene calculated in the π-SCF approximation, and the corresponding dipole and rotational strengths obtained by the dipole-velocity method, show that the optical isomer studied has the M-configuration with the stereochemical form of a segment of a left-handed helix. Analogous calculations in the INDO approximation using both the dipole-velocity and the dipole-length procedure with separate consideration of the one-centre and the two-centre transition moment integrals, indicate that the more satisfactory dipole and rotational strengths are obtained in the two-centre dipole-velocity formulation. The appearance of σ → π* transitions at higher energies limits the application of the π-SCF procedure, but the INDO method is found to place these transitions at too low an energy.

ISSN:0026-8976    

DOI:10.1080/00268977100100771

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

The intensity and spectra of light scattered from nitrobenzene-benzene mixtures have been studied at 24±1°C. The anisotropic Rayleigh ratio shows a non-linear variation with concentration, attributed to strong orientational correlations between nitrobenzene molecules.

ISSN:0026-8976    

DOI:10.1080/00268977100100781

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

The Zeeman effect of theRabsorption lines for the pure compound 2[Cr(en)3Cl3]KCl.6H2O has been measured photographically, using a strong pulsed magnet with fields of up to 200 000 gauss at 77 K. The results indicateg∥(4A2) = 1·82 ,g⊥(4A2) = 1·90 withg∥(Ē) = -1·82 andg∥(2Ā) = 1·82. The uncertainties are of the order of ± 0·05.

ISSN:0026-8976    

DOI:10.1080/00268977100100791

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

Expressions are derived for the rotational energy levels of a symmetric top molecule in a2Estate which take into account a spin-orbit interaction and vibronic Jahn-Teller interactions. Some group theoretical aspects of the Jahn-Teller problem for a general symmetric top molecule are discussed. In addition, the overall selection rules and formulae for the relative intensities of rotational lines in a2A-2Etransition are derived and the possibility of applying them to two recently published experimental examples is considered.

ISSN:0026-8976    

DOI:10.1080/00268977100100801

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

An account of a method of performinga prioritight-binding calculations on a crystal lattice of the diamond type is given. The method is a generalization of that of Cohanet al.[8]. Certain possible extensions of the method are discussed. New results for the electronic energy bands in diamond are presented in which the variation of the bands with the hybridization parameter of the initial bonding orbitals and the orbital exponent of the basic atomic orbitals is investigated.

ISSN:0026-8976    

DOI:10.1080/00268977100100811

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

The self-consistent field molecular orbital theory has been used to calculate the electronic structure and properties of the first ten members of the polyene series. From these results the properties of the infinite polyene are predicted.

ISSN:0026-8976    

DOI:10.1080/00268977100100821

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

An analysis ofO(4) andU(3) symmetry classified states and their contribution to configuration mixing between 3s2-3pn-2and 3pnfunctions is made through a global group-theoretical study of second-row atoms (Na, Mg, Al, Si, P, S, Cl, Ar) and their ions. This permits us to estimate the amount of symmetry breaking due to electronic repulsions in these systems. TheO(4) eigenstates give consistently better overlaps with the exact intrashell (3s-3p) functions thanU(3), which is striking if one remembers that the results for first-row atoms are exactly the opposite. This ‘partial recovery ofO(4) symmetry’ is consistent with the tendency ofO(4) to improve with the number of electrons and may prove to be useful. However, if we introduce innershell effects theO(4) scheme is spoiled and in fact it isU(3) which gives a better approximation to unrestricted Hartree-Fock functions for 3s-3pcomplexes. These results are discussed and analysed with regard to their future possibilities.

ISSN:0026-8976    

DOI:10.1080/00268977100100831

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

The H(1s)-H+, He-He, H(1s)-H(1s) and H(1s)-H(2s) interactions are considered as model systems for investigating the use of the Padé approximation method in summing theR-1intermolecular force series. Various Padé approximants and partial sums of theR-1expansions of the second-order Coulomb interaction energies are compared with the corresponding non-expanded results for each interaction. The computations are based on Unsöld's average energy approximation and on exact results for the H(1s)-H interaction. The results indicate that the Padé approximation method is a simple, useful way to remove some of the difficulties associated with the slow rate of convergence of theR-1force series but that it does not alleviate the problems associated with the asymptotic divergent nature of the series. The results for the H(1s)-H+interaction illustrate a possible difficulty in using Unsöld's method in the calculation of interaction energies.

ISSN:0026-8976    

DOI:10.1080/00268977100100841

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

Neutron diffraction structure factors for liquid carbon tetrachloride and germanium tetrabromide have been measured and are analysed to determine the molecular centre positional correlation function allowing for molecular angular correlation. The analysis shows quite unequivocally that appreciable molecular orientational correlations must exist in these liquids but that it may only extend to nearest neighbours. This is thought to cause the pair distribution function for the molecular liquids to be markedly different from that for atomic liquids such as argon and the difference is discussed.

ISSN:0026-8976    

DOI:10.1080/00268977100100851

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor