Energy exchange rate coefficients from vibrational inelastic O2(Σg−3) + O2(Σg−3) collisions on a new spin-averaged potential energy surface

Abstract

A new spin-averaged potential energy surface (PES) for non-reactive O2(Σg−3) + O2(Σg−3) collisions is presented. The potential is formulated analytically according to the nature of the principal interaction components, with the main van der Waals contribution described through the improved Lennard-Jones model. All the parameters involved in the formulation, having a physical meaning, have been modulated in restricted variation ranges, exploiting a combined analysis of experimental and ab initio reference data. The new PES is shown to be able to reproduce a wealth of different physical properties, ranging from the second virial coefficients to transport properties (shear viscosity and thermal conductivity) and rate coefficients for inelastic scattering collisions. Rate coefficients for the vibrational inelastic processes of O2, including both vibration-to-vibration (V–V) and vibration-to-translation/rotation (V–T/R) energy exchanges, were then calculated on this PES using a mixed quantum–classical method. The effective formulation of the potential and its combination with an efficient, yet accurate, nuclear dynamics treatment allowed for the determination of a large database of V–V and V–T/R energy transfer rate coefficients in a wide temperature range.

Vibrational Energy Transfer in CO+N2 Collisions: A Database for V–V and V–T/R Quantum-Classical Rate Coefficients

“…The formulation of the full PES is essentially the same one of [ 18 ], which will be briefly described in the following. The approach, which has been successfully applied to O -O [ 21 ], N -N [ 13 , 31 ], N -H [ 32 ], and CO -CO [ 33 ], expresses the potential function parameters in terms of the binding energy and internal molecular structure (intramolecular part) and of properties like charge distributions and polarizabilities (intermolecular part).…”

“…For this reason, the quantum-classical (QC) approach, sometimes also referred to as semiclassical, has been used over the years for the description of inelastic scattering in a variety of diatom–diatom systems: N +N [ 10 , 11 , 12 , 13 ], CO+CO [ 14 , 15 ], N +CO [ 11 , 16 , 17 , 18 ], O +O [ 19 , 20 , 21 ], etc. leading, in some cases, to the creation of large databases for V–V rate coefficients.…”

“…V–T/R rates are believed to play a less important role than V–V ones, particularly when the latter involve nearly resonant energy exchange, but this is usually true in the low-temperature regime only. High-temperature conditions and high vibrational quantum numbers greatly favor V–T/R processes and, as we highlighted in recent investigations on N -N [ 13 ] and O +O [ 21 ], they can even become the most favorable events, heavily contributing to the overall molecular vibrational distribution. Such temperature regimes are those characterizing, for instance, hypersonic flows around re-entry vehicles.…”

“…The present study aims to provide a large database of V–V and V–T/R rate coefficients for collisions between molecular nitrogen N and carbon monoxide CO, calculated through the mixed quantum-classical method [ 7 , 8 , 9 , 13 , 14 , 21 ]. A detailed database for V–V processes, including some multiquantum transitions, calculated through the QC method, is available up to T = 2900 K [ 11 ].…”

“…In order to produce an accurate database, in the present study we start by improving the above PES, according to a procedure we successfully applied in the case of N -N [ 13 ], O -O [ 21 ], and N -O [ 30 ] systems. Indeed, one of the main advantages of this analytical formulation, which is far from being a simple fit to ab initio or experimental data, is the possibility of modulating its behavior by modifying the physically meaningful parameters in a limited range.…”