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A new multiproperty potential energy surface for the N2–Ar intermolecular interaction is reported. The present determination is based upon molecular beam total differential and integral scattering data, taken together with the temperature dependence of the interaction second virial coefficient, transport properties, transport property field effects, and relaxation phenomena, such as pressure broadening of the depolarized Rayleigh line and longitudinal nuclear spin relaxation. The primary fit has been made to the beam scattering and virial data, and refinements to the potential parameters thus determined have been made by employing the data available for the gas phase transport and relaxation phenomena. The potential energy surface employed is an empirical Morse–Morse–spline–van der Waals form, in which the potential parameters depend upon the angle between the N2 figure axis and the line joining the centers of mass of N2 and Ar. No N2 stretching dependence has been included in the present determination. Comparison is made between the present potential energy surface and two other previously published N2–Ar potential energy surfaces. The present potential energy surface provides the best overall agreement for all available gas phase data for N2–Ar mixtures, and can thus be recommended for calculations of all properties of such mixtures that depend upon the intermolecular interaction. [ABSTRACT FROM AUTHOR]

A detailed comparison of the predictive powers of two recently determined empirical and two recently proposed theoretical potential energy surfaces for the N2–He interaction has been carried out. In particular, the following properties have been tested: at the microscopic level, total and state-to-state differential cross sections and absolute total integral cross sections, while at the macroscopic level, interaction second virial, diffusion, viscosity, and thermal conductivity coefficients, as well as the rotational relaxation time, depolarized Rayleigh spectral collision broadening, and shear viscosity and thermal conductivity field-effect data in N2–He mixtures. Exact calculations have been employed, from the close-coupling method for treating scattering data at low energies to the classical trajectory method with second-order corrections to compute the effective cross sections that determine the bulk transport and relaxation phenomena.The empirical exponential-spline–Morse-spline–van der Waals surface [J. Chem. Phys. 85, 7011 (1986)], closely followed by the model Bowers–Tang–Toennies surface [J. Chem. Phys. 88, 5465 (1988)], gives better simultaneous agreement with the scattering data, the second virial coefficient data, the bulk transport data, and the depolarized Rayleigh collision-broadening data, which are properties sensitive to the spherical component of the interaction and to the anisotropy of the low repulsive wall. None of the potential surfaces examined here includes a dependence upon the vibrational stretching coordinate of the N2 molecule, since none of the data employed in the fitting is sensitive to this coordinate. The two theoretical model potentials, especially that based upon an earlier Hartree–Fock plus damped dispersion model surface [J. Phys. Chem. 88, 2036 (1984)], gives better agreement with the rotational relaxation and field-effect data, which are properties sensitive to the... [ABSTRACT FROM AUTHOR]

A singular value decomposition is used to determine how much and what kind of information about a potential surface is obtainable from a given set of measurements. From the functional sensitivities which relate a set of observable cross sections to the potential, an orthogonal set of potential variations is produced which provides a basis set for describing errors in the potential model. Corresponding to each basis function is an image vector representing a linear combination of cross sections which is the observable response to that particular correlated potential variation. The inclusion of realistic models of measurement uncertainties and potential model uncertainties in the analysis makes possible the division of the potential variation space spanned by the potential variation basis into (i) a subspace of measurable model errors and (ii) a complementary subspace of model errors which the proposed measurements will be unable to estimate. The analysis procedure may be used to assess the value of proposed measurements for inversion, and the technique is compatible with an allied inversion method under development. The method is illustrated for the He–H2 rigid rotor system using as observables a candidate set of generalized cross sections which could be obtained from measurements of viscosity and thermal conductivity in the presence and absence of a magnetic field. The set of observables considered here is found to be capable of providing five distinguishable pieces of information, primarily about the repulsive potential wall and its anisotropy. Field effect measurements of the quality now available are thus shown to offer a means for refining existing models of the anisotropy of the rare-gas-diatom interaction. [ABSTRACT FROM AUTHOR]

A high-level ab initio -based ground-state Ar-O 2 potential energy surface has been obtained and employed to predict the microwave (MW) spectrum of the Ar-O 2 van der Waals complex. Transferability of the atom-atom components of the total interaction has been explored by extrapolating the original ab initio potential energy surface via accurate ArO and ArN potentials deduced from the rotational parameters of the Ar-NO and Ar-N 2 Van der Waals complexes. The extrapolated Ar-O 2 potential energy surface has then been tested by comparison with experimental Ar-O 2 scattering data. In addition, the extrapolated potential energy surfaces have been compared with other ab initio -derived and empirical atom-atom and atom-molecule potential energy surfaces in the literature. [ABSTRACT FROM AUTHOR]

The ground state Ar-Br2 potential energy surface is predicted from ab initio calculations and from an atom-atom model using empirical ArBr potentials and the (evaluated ab initio ) perturbation of the interaction between Ar and Br within Br2. At all levels of modelling, the surface has a double-minimum topology, with wells for both the linear (L-) and T-shaped geometries. This differs from the single-minimum topology predicted by the commonly used pairwise additive Lennard-Jones potential. For both ab initio and atom-atom model surfaces, the L well is found to be significantly deeper than the T well; this relative behaviour is unchanged by zero-point vibrations. Spectroscopic parameters are predicted for the present surfaces. The final surfaces result from a scaling to reproduce the estimated bond energy of the system. Possible reflections of the surface topology in experimental observables are discussed. [ABSTRACT FROM AUTHOR]