摘要:

A computer simulation has been obtained of the atom recombination reaction in which the recombination energy is removed by a third-body. The equations of classical dynamics have been solved for two iodine atoms and six inert gas atoms (He, Ar or Xe) confined to a spherical vessel by a wall potential which is a spatial average of a spherical shell of inert gas atoms. Reactions at a given temperature and concentration are simulated by varying the initial momenta of the atoms and the volume of the sphere. A computer run of 100 trajectories for each physical situation gives the average time for recombination, and from this a macroscopic rate constant has been calculated that agrees well with the experimental result. The model reproduces all the characteristic kinetic mechanisms that have traditionally been used to interpret atom recombination. However, at high inert gas concentrations the steady-state approximation is shown to fail as many of the important intermediate reactions do not reach equilibrium. In this high concentration region the fall-off of the recombination rate constant is discussed in terms of a diffusion controlled mechanism.

ISSN:0026-8976    

DOI:10.1080/00268977700103001

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

The differential scattering cross section for neutron scattering from liquid heavy water (D2O) has been measured at incident neutron wavelengths of 0·694 and 0·347 Å. The oscillatory pattern observed at high momentum-transfer values characterizes the structure of an individual molecule. The data are found to be in good agreement after application of a correction for molecular recoil and give a value of 0·98 ± 0·01 Å for the oxygen-deuterium bond length.

ISSN:0026-8976    

DOI:10.1080/00268977700103011

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

The phosphorescent state of pyrazine has been studied with theT → Semission andT ← Sexcitation methods in combination with microwave techniques in the systems of pyrazine-h4in pyrazine-d4, pyrazine-h4and -d4inp-dioxane,p-xylene, and benzene, and pyrazine-h4x-trap. The three out-of-plane hydrogen bending vibrations ofv10a,v5andv17aare found to be active in theTxsublevel emission of the isotopic mixed crystal. By modifying the force constants used by Scully, the frequencies of the out-of-plane vibrations were reexamined and the result was compared with the observed frequencies.

ISSN:0026-8976    

DOI:10.1080/00268977700103031

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

The problem of calculating singlet states with two non-degenerate singly occupied orthogonality-constrained orbitals is investigated. The generalized Brillouin condition of Levy and Berthier leads to problems of accuracy and convergence and may even yield energies far below a variational upper bound. An alternative condition is formulated requiring the cancellation of energy contributions from the interaction with single excitations between the open shells. In calculations using this condition accuracy and convergence is considerably improved although strict upper bounds to the energy are not obtained. Test calculations for some simple molecules show the utility of the new method.

ISSN:0026-8976    

DOI:10.1080/00268977700103041

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

ISSN:0026-8976    

DOI:10.1080/00268977700103051

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

The density profiles for a hard-sphere fluid in front of an ideal wall obtained either with the Percus-Yevick or the superposition approximation are compared. In an expansion of the profile in powers of the bulk density, the coefficient of the third power is better in the superposition approximation. The density at the wall is given exactly by the superposition approximation, whereas the Percus-Yevick result is too low. For the superposition approximation a calculated density profile and the excess surface density as function of the bulk density are also given.

ISSN:0026-8976    

DOI:10.1080/00268977700103061

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

The analysis of the Fourier transform spectrum, with a resolution of 0·008 cm-1, of the combination bands ν2+ ν3(A1species) and ν3+ ν5(Especies) of CH3F has allowed the study ofx-yCoriolis resonance between the states υ2= 1 and υ5= 1. The vibrational levels υ2= υ3= 1 and υ3= υ5= 1 are 15 cm-1apart and the interaction is very strong. The combination of the Coriolis resonance and the essential interaction ofl-type (2, 2) in ν3+ ν5gives rise to a ‘giant’l-type doubling : forJ=25 the shift between the levels is about 17 cm-1.

ISSN:0026-8976    

DOI:10.1080/00268977700103071

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

Previous work on fluids of polar polarizable molecules is extended. Simplification is obtained by eliminating the direct correlation functionc(12) in favour of a translationally invariant functionw(12) defined previously, and by consolidating equations in matrix form. Two closely related problems are the asymptotic form of the pair correlation functionh(12), and the calculation of microscopic expressions for the dielectric constant in a form which manifestly exhibits the required independence of the shape of the system. The solution is obtained by a procedure which formally exactly parallels the case of rigid polar molecules, with matrices replacing numbers. The connection between the chemical potential and the renormalization of the dipole moment and the polarizability is pointed out and utilized to obtain an expression for the excess Helmholtz free energy ΔAdue to dipolar forces. The SSC approximation is examined; it is found that ΔAcan be calculated directly from the solution of the SSC equation at a single density and temperature without explicit integration over a coupling parameter. Similar results for the pressure and internal energy are given.

ISSN:0026-8976    

DOI:10.1080/00268977700103081

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

Reorientations of the CH3groups and of the cation are studied in the two phases (phase transition at 308 K) of (CH3)3NH+Cl-by quasielastic neutron scattering using a time of flight and a backscattering instrument. In the high temperature phase the experimental results can be described by rotational diffusion of the cation around its threefold axis withDr= 0·49 × 1012s-1(τc= 1/Dr= 2·05 ¢ 10-12s) at 333 K. The reorientation of the methyl groups is too slow to produce in this phase a quasielastic broadening detectable by the time of flight experiment. In the low temperature phase the observed spectra can be explained by simultaneous 120° jumps of the cation and of the methyl groups. The correlation times for the two reorientations are about the same: τc≈ 4 × 10-10s at 273 K.

ISSN:0026-8976    

DOI:10.1080/00268977700103091

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

A jump model is developed which describes simultaneous, dynamically uncorrelated reorientational motions of a proton about two different threefold axes. For the spectrum of quasielastic neutron scattering a superposition of three lorentzians with linewidths of 1/τ1, 1/τ2, and 1/τ*=1/τ1+ 1/τ2is obtained as quasielastic broadening. The model is applied to describe the reorientations of the cation (CH3)3NH+and of the CH3groups in (CH3)3NH+Cl-.

ISSN:0026-8976    

DOI:10.1080/00268977700103101

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor