G. Liuti

Range, strength and anisotropy of intermolecular forces in atom–molecule systems: an atom–bond pairwise additivity approach

Abstract A new method is proposed to calculate bond energies and equilibrium distances in atom–molecule van der Waals complexes which arises from a balancing between long-range attraction and asymptotic tail of the repulsion. The method, based on correlation formulas between the polarizability of the interacting partners and the main interaction parameters, is an extension of an approach originally developed for atom–atom cases. The basic idea exploits the concept of bond polarizability additivity to represent both the molecular repulsion, in terms of a size which is mainly ascribed to the molecular bonds nearest to the probe atom, and the molecular attraction as due to multi-dispersion centers delocalized on the molecular frame. The method, mainly tested on hydrocarbon–rare gas complexes, can be considered as the starting point for the study of systems of higher complexity.

Generalization to ion—neutral systems of the polarizability correlations for interaction potential parameters

Abstract Correlations in terms of particle polarizabilities are developed for both positive and negative ion—neutral interactions extending a general scheme previously proposed. For a proper assessment of the parameters, the ratio of the dispersion to the induction energy is evaluated in terms of the polarizability of the interacting partners. The correlations are successfully tested for a variety of ion—neutral systems. Their use to predict the potential parameters of unknown systems is suggested.

Regularities in van der Waals forces: correlation between the potential parameters and polarizability

Abstract An analysis of regularities in the van der Waals forces has been performed for over fifty systems. Correlations are found between features of the interaction, namely the well depth and its location, and atomic properties such as the polarizability. These correlations can be extended to the spherical part of the interaction of anisotrophic systems, and can be used to estimate potential parameters for species that are difficult to study experimentally.

Study of the interactions of atomic and molecular oxygen with O2 and N2 by scattering data

Absolute total scattering cross sections for the O2–O2, O2–N2, O–N2, and O–O2 systems are measured in the thermal energy range. A glory structure is present for O2–O2, O2–N2, and O–N2. For O–N2 this structure appears to be partially quenched due to the anisotropy of the 3P oxygen atom. For O–O2 the structure is almost completely quenched because of the presence of a manifold of interactions. From the analysis of the cross section data, information about the interaction potential of all these systems of atmospheric interest is obtained. For O2–O2 a potential able to reproduce also the spectroscopic and thermophysical data is proposed.

Absolute total elastic cross sections for collisions of oxygen atoms with the rare gases at thermal energies

Absolute total elastic cross sections for collisions of ground state O atoms with He, Ne, Ar, Kr, and Xe have been measured as a function of velocity in the range 0.6–2.0 km sec−1. The data are deconvoluted in the center‐of‐mass system and treated in terms of model potentials for the involved interactions. For the heavier rare gases a glory structure has been observed and the possible role played by multiple potentials on such structure is discussed.

The interaction of atomic and molecular nitrogen with argon by scattering measurements

Absolute integral cross sections for collisions of N2 molecules and N atoms with Ar are measured as a function of velocity at thermal energies. For the N2–Ar case the glory structure observed in the cross section vs velocity plot does not appear to be affected by the anisotropy of the interaction. An analysis in terms of a spherically averaged potential model can be performed thus obtaining a reliable potential function. The N–Ar cross sections presented here are the first collisional study of N atoms leading to significant information on the interaction potential. Although, as shown by the magnetic behavior, the N atom beam is essentially a mixture of atoms in the two metastable 2DJ and 2PJ states, the results obtained, together with other properties of the excited atoms, indicate the presence of a low anisotropy in the N–Ar interaction. An analysis in terms of a simple and yet realistic potential model has been performed obtaining meaningful potential parameters for the N–Ar system. The results for N–Ar...

Scattering experiments on the methane-rare-gas interaction

Abstract Absolute integral cross sections for collisions of CH 4 with Ne, Ar, Kr and Xe are measured as a function of velocity at thermal energies in a molecular beam apparatus. The presence of fully developed glory oscillations indicates that the anisotropy of methane plays only a minor role in these experiments. The data can therefore be treated in terms of a central force-field assumption. The validity of this assumption is confirmed by comparison with the behaviour of other systems through a correlation between the potential parameters and the polarizabilities.

Absolute total cross sections for scattering of hydrogen atoms by argon, krypton and xenon

Abstract Absolute total cross sections for scattering of hydrogen atoms by argon, krypton and xenon were measured as a function of velocity in the range from 1.8 to 6.2 km/sec. An analysis in terms of Lennard-Jones (12.6) and (8.6) model potentials leads to estimates of the interatomic forces.

Scattering experiments on the interaction of atomic and molecular nitrogen with krypton

Absolute integral cross sections for collisions of N2 molecules and N atoms with Kr are measured as a function of velocity at thermal energies. For the N2Kr case the glory structure observed in the plot of cross section versus velocity is only slightly affected by the anisotropy of the interaction. An analysis in terms of a spherically averaged potential model can be performed, thus obtaining a reliable potential function. For the NKr system the occurrence of a well developed glory oscillation indicates low anisotropy in the interaction. An analysis in terms of a simple, realistic potential model has been performed to give potential parameters for the NKr system.