Franco Vecchiocattivi

The N2Ar potential energy surface

Abstract The potential energy surface for the N 2 Ar system has been obtained assuming a spherical average interaction previously reported from this laboratory. The angular dependence has been assessed by a combined analysis of the integral and differential scattering cross sections and sonic spectroscope data. The potential energy surface is given via a parametric model. A similar potential energy surface for O 2 Ar has been obtained with the same procedure. This surface is an improvement of an earlier one, because it reproduces the differential total cross sections recently measured.

Improved potential energy surface for He–CO2

The anisotropic potential energy surface of He–CO2 is determined by the simultaneous analysis of newly measured high resolution total differential cross sections, differential energy loss spectra, new low temperature second virial coefficients, new diffusion, and viscosity data. The calculations are carried out in the infinite‐order‐sudden approximation. The repulsive anisotropy of the potential is determined from the rotationally inelastic cross sections and the quenching of the diffraction oscillations, while the absolute scale is fixed by the position of these oscillations. The second virial coefficient data are essentially sensitive to the general features of the spherical effective potential well. The transport data are then correctly predicted by this potential surface which differs both in the anisotropy and the spherical part from the recently derived multiproperty fit potential for this system.

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.

Orientational and spin–orbital dependence of interatomic forces

The representation of weak interactions of open-shell atoms as effective anisotropic potentials is discussed. Examples, mainly from recent molecular-beam studies of collisions of magnetically orientated atoms in P states, prove that the spherically averaged component of the interactions follows systematics established for closed-shell van der Waals forces. Data are being collected to unravel similar systematic trends for the anisotropic component of the interactions.

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.

Velocity dependence of the cross section for Penning and associative ionization of argon atoms by metastable neon atoms

Relative cross sections for Penning and associative ionization in Ne*(3P2,0)–Ar collisions have been measured, in a crossed beam experiment, as a function of the collision velocity, in the thermal energy range. The total ionization cross sections have been analyzed, together with other experimental results, obtaining a best fit resonance width function. The analysis of the associative to Penning ionization cross section ratios shows that, in the high collision energy range, the ionization occurs predominantly through the 2Σ1/2 ground state of NeAr+ ion. Some considerations on the role played by the interaction anisotropy in these ionization processes are reported.

An intermolecular potential for nitrogen from a multi-property analysis

New measurements are reported for the velocity dependence of the integral cross-section for N2–N2 scattering showing the glory oscillations. These data are analysed along with recent high precision second-virial coefficient data and traditional transport property measurements to yield an improved N2–N2 potential energy surface by adjusting certain parameters in the fit to this surface by van der Avoird et al. The new potential gives improved agreement with the integral cross-section, virial and transport data. Transport and relaxation cross-sections sensitive to anisotropy are very close to those obtained previously using the van der Avoird et al. surface. New comparisons with rotational relaxation and NMR relaxation data are reported.

A fast and accurate semiclassical calculation of the total elastic cross section in the glory energy range

A method for the semiclassical calculation of the total cross section in atomic and molecular elastic collisions, for the glory energy range, is reported. The parameters needed for the calculation of the glory undulatory component of the cross section are obtained from a few JWKB phase shifts for impact parameters near the glory impact parameter. The smooth component of the cross section is obtained from JB phase shifts for the long range attraction. The procedure, suitable for every potential model, is accurate and much faster than a full JWKB calculation. A discussion of some typical results is reported and an analysis of the information obtainable from experimental absolute cross sections is also given.

The interaction potential energy surface of O2Ar

Abstract A potential energy surface for the O 2 Ar system has been obtained by a multiproperty analysis. The absolute integral cross sections at thermal energy, the high energy scattering cross sections, the second virial coefficients, and the P and R branches in the absorption infrared spectrum of the O 2 Ar van der Waals molecule, have been analyzed in order to obtain the isotropic component of the interaction. This average potential curve shows a minimum of 11.5 meV at 3.72 A. The quenching of glory structure and some features of the infrared spectrum have been used to extract information on the anisotropic component.

Absolute total elastic cross sections for O2-rare gases scattering

Absolute total elastic cross sections for collisions of O2 with He, Ne, Ar, Kr, Xe have been measured in the velocity range from 0·4 to 2·4 km s-1. Except in the O2-He system, all the cross sections show a glory structure, and the van der Waals constants, C 6, have been obtained from the average ∼ν-2/5 dependence. Total cross sections have been well reproduced by some usual spherically symmetric potential models. Detailed information on the spherical portion of the interaction potential, in the range of the limiting impact parameters, have been extracted.