Closer versus Long Range Interaction Effects on the Non-Arrhenius Behavior of Quasi-Resonant O₂ + N₂ Collisions

Abstract

We report in this paper an investigation on energy transfer processes from vibration to vibration and/or translation in thermal and subthermal regimes for the O + N system performed using quantum-classical calculations on different empirical, semiempirical, and ab initio potential energy surfaces. In particular, the paper focuses on the rationalization of the non-Arrhenius behavior (inversion of the temperature dependence) of the quasi-resonant vibration-to-vibration energy transfer transition rate coefficients at threshold. To better understand the microscopic nature of the involved processes, we pushed the calculations to the detail of the related cross sections and analyzed the impact of the medium and long-range components of the interaction on them. Furthermore, the variation with temperature of the dependence of the quasi-resonant rate coefficient on the vibrational energy gap between initial and final vibrational states and the effectiveness of quantum-classical calculations to overcome the limitations of the purely classical treatments were also investigated. These treatments, handled in an open molecular science fashion by chaining data and competencies of the various laboratories using a grid empowered molecular simulator, have allowed a rationalization of the dependence of the computed rate coefficients in terms of the distortion of the O-N configuration during the diatom-diatom collisions. A way of relating such distortions to a smooth and continuous progress variable, allowing a proper evolution from both long to closer range formulation of the interaction and from its entrance to exit channel (through the strong interaction region) relaxed graphical representations, is also discussed in the paper.

Collisional O2+ N2State-Selected Cross Sections for Open Science Cloud Reuse

“…This is instead what the open science nature of MOSEX needs: process variables and PES representations biased toward a full-range description of the system involved. After all, the already mentioned functional representation of the MN PES designed to properly describe at the same time high-energy processes (such as the dissociative ones) and the long-range nature of the O 2 and N 2 interactions (as previously done in N 2 –N 2 studies ,− using bond–bond models , for thermal and subthermal collisions − ) motivated us, as we shall describe later when analyzing rotationally state-specific and thermalized rate coefficients, to exploit the versatility of the already mentioned BO variables.…”

Electrically Excited, Supersonic Flow Carbon-Monoxide Laser with Air Species in Laser Mixture

“…The rates have been modified taking into account measurements and semiclassical trajectory calculations of V-V rates for CO-CO [19,20] [30,31], and N 2 -O 2 [32]. Although more recent calculations of N 2 -O 2 V-V rates [33], using a more accurate potential energy surface [34], are available, at the present conditions the effect of V-Vexchange between N 2 and O 2 on predicted CO vibrational level populations and laser power is very weak because high vibrational level populations of nitrogen and oxygen are extremely low (see Sec. IV).…”

The role of the long-range tail of the potential in O2 + N2 collisional inelastic vibrational energy transfers

“…32 Attempts to unify the formulation of V intra and V inter in terms of bond order variables are also being carried out. 31 On the contrary, the MN PES is based on the massive calcu lation of a dense grid of 55,000 high level ab initio points and on their fitting using polynomials in mixed exponentialgaussian variables. 23 As already mentioned, while this allows the simul taneous description of all the possible rearrangements and frag mentations of the O 2 + N 2 system, does not provide sufficient information to accurately describe the longrange interaction and enable a proper evaluation of nonreactive rate coefficients at thermal and subthermal conditions.…”

“…A more quantitative analysis of the impact of such inaccuracy of the computed value of the O 2 + N 2 rate coefficients for in elastic vibrational energy transfer in conditions in which neither atom exchange nor fragmentation occurs is the central goal of the present paper and is instrumental to ground our ongoing QCT and Quantum Classical studies of thermal and subthermal pro cesses. 31 Accordingly, the paper is articulated as follows: In sec tion 2 the key differences of the nonreactive outcomes of QCT calculations performed on both the MF2 and the MN O 2 + N 2 PESs are discussed. In section 3 a detailed analysis of the features of the PESs used for the calculations with respect to some exper imental and theoretical information discriminant for the class of processes of our interest is performed.…”