Transition probabilities have been calculated as a function of vibrational and rotational level for the A2Σ+−X2πi system of the hydroxyl molecule. The wavefunctions are obtained from RKR calculations. The electronic transition moment is constructed by adding a small hyperbolic tail at large internuclear distance r (taken from an ab initio calculation) to a linear form at small r; this linear form was validated in earlier studies by laser-excited fluorescence measurements, calculations, and an examination of literature data. The results show, as anticipated, a variation in transition probability with rotatinaal quantum number J, the degree of which varies with vibrational band. The widely used results of Anketell and Learner, based on an inferior form of the transition moment, are accurate to within about 10% for the range J = 0−20 within a given vibrational band, although not from band to band.

Calculated rotational transition probabilities for the A−X system of OH

Theory of physisorption interactions

Publisher Summary This chapter gives an account of the physics of gaseous diffusion of atoms and molecules, and to survey the experimental methods and results obtained in the determination of gaseous diffusion coefficient. Diffusion is the most difficult of the three transport mechanisms to define satisfactorily, because it is most convenient to define a diffusion coefficient for a mixture in which the net flux is zero and in which there is also no pressure gradient. The computation of the viscous flux for gases is carried out exactly as in the case of liquids to obtain Poiseuille's law, but remembering that a gas is compressible. Although it is easy enough to write down the phenomenological equations for multi-component diffusion, it is very difficult to solve them. Multi-component diffusion is much more complicated than binary diffusion; even ternary diffusion shows qualitatively different features than binary diffusion.

The diffusion of atoms and molecules

A family of combination rules, from which van der Waals coefficients for interactions between unlike molecules may be estimated in terms of those for the corresponding like interactions and the static polariabilities, is tested empirically and related to an approximate parameterization of the frequency‐dependent polarizability function. The treatment includes two‐ and three‐body dipole force constants and the higher‐multipole terms of the second‐order two‐body dispersion energy. The rules give agreement within a few percent (about the same accuracy as the input data) when compared with accurate unlike coefficients for systems involving H, He, Ne, Ar, Kr, Xe, Li, Na, K, Rb, Cs, Hg, H2, N2, CH4, He(21S), He(23S), He+, Li+, Na+, K+, Rb+, Cs+. Knowledge of n like coefficients and polarizabilities permits calculation of n(n − 1) / 2 unlike two‐body and n(n − 1)(n + 4) / 6 unlike three‐body force constants.

Combination Rules for van der Waals Force Constants

This paper contains the background for a complete synthesis of all the properties-equilibrium as well as transport—of the five noble gases and of the 26 mixtures that can be formed with them. The synthesis is valid for the zero-density limit only, but covers the temperature range from absolute zero to the onset of ionization. The synthesis is based on a thorough revision of the two-parameter extended law of corresponding states of Kestin, Ro and Wakeham. The paper recalls the basis for the original corresponding-states principle, identifies the places at which experiment and the theory of statistical mechanics suggest deviations, and proceeds to remove them to a point where almost perfect agreement between calculation and a very large body of diverse experimental data is achieved, in the sense that deviations of experimental data from calculation are of the same order as the uncertainty in the best contemporary measurements. The basis of the revised corresponding-states principle is a set of five parameters which characterize each pair-interaction together with a fully consistent and asymptotically correct set of universal collision integrals and functionals that appear in the rigorous theory. These are reinforced with selected quantum-mechanical calculations applied in regions where they are significant.

Improved corresponding states principle for the noble gases

Intermolecular force determination methods, discussing model construction, experimental data analysis, quantal calculations, spectroscopic observations and beam scattering

Methods for the Determination of Intermolecular Forces

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Methods for the Determination of Intermolecular Forces