摘要:

The structure factorSm(Q) for liquid carbon suboxide has been determined for aQ-value range of 0·4 to 60 Å-1by neutron diffraction measurements using a steady-state (reactor) and a pulsed (linac) neutron source. The bond lengths of the molecule have been determined from the data and give good agreement with the results of electron diffraction measurements on the vapour phase after application of a molecular recoil correction term. The quasi-linear nature of the molecule is confirmed but the shape of the form factor indicates that large amplitude bending motion probably occurs in the liquid phase.

ISSN:0026-8976    

DOI:10.1080/00268977800102611

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

The isotropic linewidths of a series of overtones in the resonance Raman spectrum of a dilute solution of I2and CCl4were measured. The widths enabled the mechanism responsible for the vibrational dephasing to be identified as a vibrational frequency modulation. The transition between the fast and slow modulation regimes could be followed, by observing the dependence of overtone width on overtone order, and a characteristic time and mean square amplitude ascribed to the frequency modulation process.

ISSN:0026-8976    

DOI:10.1080/00268977800102621

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

The fundamental work of Balslev, Combes, and Simon has provided a mathematical foundation for the description of atomic and molecular resonances by the complex-rotation method. In the present paper we discuss some formal properties of the complex-rotated hamiltonian operators and the variational criteria for the approximation of their resonance eigenvalues. These criteria are employed in numerical studies of the complex-rotation method, which is illustrated and compared with various stabilization procedures in an application to a simple model potential. We propose a virial-scaling procedure for determining variationally optimal estimates of the resonance position and lifetime and apply the technique to the helium (2s)2auto-ionizing resonance. Our results lend support to the idea that resonance features in the continuous spectrum can be successfully described by techniques similar to those employed for bound states.

ISSN:0026-8976    

DOI:10.1080/00268977800102631

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

The theory presented in this paper investigates the isotropic Raman spectra of liquid binary mixtures. It is found that thecollectivevibrational modes of different molecular species can be significantly coupled. This is a consequence of the (nearly) resonant vibrational transfer processes, which give rise to distinct vibrational correlations (i.e. correlations between adjacent molecules). The coupling, however, occurs only with weakly-separated or overlapping bands. The more general results of the theory are applied to isotope mixtures. The spectral information available from relevant dilution experiments is interpreted. In particular it is shown that the spectral properties of the vibrationalself-correlation part can be concluded from the observed collective correlation function. The significance of thedistinctvibrational correlations with respect to the infrared and depolarized Raman spectra is discussed.

ISSN:0026-8976    

DOI:10.1080/00268977800102641

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

Anharmonic lattice vibration in solid γ-N2has been studied in terms of a Green's function perturbation method. The crystal hamiltonian is made up of a 12–6 atom-atom potential. Phonon band shapes of external lattice vibrations atq= 0 have been computed at several temperatures up to 40 K at a constant molar volume of 24·09 cm3. It is found that the calculated band maximum frequencies of Raman-active modes,EgandB1g, decrease with increasing temperature, which is consistent with experiment, while the frequencies of the other modes increase. The temperature dependence of the relative intensity,I(Eg)/I(B1g), is compared with experiment.

ISSN:0026-8976    

DOI:10.1080/00268977800102651

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

The optical and d.c. Kerr constants have been measured in the isotropic phase of 4-n-pentyl-4′-cyanobiphenyl (5CB) as a function of temperature and in 5CB/CCl4solutions as a function of concentration. By using the pulsed method dynamic properties have been determined. From the solution measurements the permanent dipole moment and optical polarizability have been determined and a critical concentration behaviour observed. The predictions of the Landau-de Gennes model for pretransitional behaviour have been examined in the isotropic phase and it has been shown from both the Kerr constants and relaxation analysis that Δnand τ are proportional to (T-T*)-1. From these results we have determined the phenomenological constanta, the viscosity coefficientv, the theoretical second order transition temperatureT* and (Tc-T*). From the differences in the relaxation data between the d.c. and optical field induced ordering we have inferred a size polydispersity for the cybotactic groups.

ISSN:0026-8976    

DOI:10.1080/00268977800102661

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

A quantum mechanical approach to type I unimolecular predissociation is developed in terms of Feshbach's optical potential. The resulting method is formally applicable to many cases of molecular breakup caused by the crossing of coupled bound and dissociative electronic surfaces. These include cases in which multiple bound and/or dissociative channels are accessible. There are two restrictions : (1) coupling among dissociative channels should be negligible, and (2) only two product fragments are allowed, of fixed atomic composition regardless of internal state. A harmonic oscillator coupled to a dissociative infinite-step or hard-sphere potential is used in comparing the usual perturbation theory results to the present approach.

ISSN:0026-8976    

DOI:10.1080/00268977800102671

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

Effects due to the time variation of the field intensity on molecular collision processes occurring in a laser field are studied. It is seen that averaging over the time profile of the intensity must be done carefully when analysing experimental results. This is particularly important if the collision takes place in a strong multimode laser field in which the intensity varies over a considerable range of values. As an illustration, a close coupling calculation is performed on a model system, and the collision cross section in a multimode laser field is compared with that in a single-mode laser field.

ISSN:0026-8976    

DOI:10.1080/00268977800102681

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

The static electric dipole polarizabilities of acetylene and ethylene are calculated using the coupled Hartree-Fock approach and the so-called electric-field-variant (EFV) GTO basis sets with explicit dependence on the external electric field strength. The results obtained for the Huzinaga-Salez-Veillard CGTO basis set comprising only s- and p-type EFV GTO's are presumably close to the corresponding Hartree-Fock limits. For the acetylene molecule (z-axis along the CC bond) the present near-HF results are αxx=18·05 a.u., and αzz=31·55 a.u. and for the ethylene molecule (y-axis along the CC bond,z-axis perpendicular to the molecular plane) they amount to αxx=24·02 a.u., αxx=36·06 a.u. and αzz=21·60 a.u. In both cases the present values are very close to the available experimental data. Also a discussion of some other recent theoretical approaches to the calculation of molecular polarizabilities is given.

ISSN:0026-8976    

DOI:10.1080/00268977800102691

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

The many-body diagrammatic Rayleigh-Schrödinger perturbation theory (RSPT) is used for the calculation of ionization potentials of open-shell systems with one unpaired electron. This theoretical approach is tested on the simple examples of NO2and NF2molecules described by the INDO semi-empirical hamiltonian. The first- and second-order results are presented.

ISSN:0026-8976    

DOI:10.1080/00268977800102701

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor