Energy transfer upon collision of selectively excited CO2 molecules: State-to-state cross sections and probabilities for modeling of atmospheres and gaseous flows

Abstract

Carbon dioxide molecules can store and release tens of kcal/mol upon collisions, and such an energy transfer strongly influences the energy disposal and the chemical processes in gases under the extreme conditions typical of plasmas and hypersonic flows. Moreover, the energy transfer involving CO2 characterizes the global dynamics of the Earth-atmosphere system and the energy balance of other planetary atmospheres. Contemporary developments in kinetic modeling of gaseous mixtures are connected to progress in the description of the energy transfer, and, in particular, the attempts to include non-equilibrium effects require to consider state-specific energy exchanges. A systematic study of the state-to-state vibrational energy transfer in CO2 + CO2 collisions is the focus of the present work, aided by a theoretical and computational tool based on quasiclassical trajectory simulations and an accurate full-dimension model of the intermolecular interactions. In this model, the accuracy of the description of the intermolecular forces (that determine the probability of energy transfer in molecular collisions) is enhanced by explicit account of the specific effects of the distortion of the CO2 structure due to vibrations. Results show that these effects are important for the energy transfer probabilities. Moreover, the role of rotational and vibrational degrees of freedom is found to be dominant in the energy exchange, while the average contribution of translations, under the temperature and energy conditions considered, is negligible. Remarkable is the fact that the intramolecular energy transfer only involves stretching and bending, unless one of the colliding molecules has an initial symmetric stretching quantum number greater than a threshold value estimated to be equal to 7.

Coupling of Plasma Chemistry, Vibrational Kinetics, Collisional‐Radiative Models and Electron Energy Distribution Function Under Non‐Equilibrium Conditions

“…Another problem arises with the new PVM dissociation constants from Equation in particular due to the dependence of heavy particle dissociation rate on the vibrational energy of CO 2 . The phenomenological approach, that considers the vibrational energy entering the Arrhenius law (see Equation ) multiplied by a factor 0.8, should be clarified especially if the non‐equilibrium vibrational distributions reported in this paper, as well as in ref., will resist to future improvements of V‐V and V‐T rates …”

Advances in non-equilibrium $$\hbox {CO}_2$$ plasma kinetics: a theoretical and experimental review

“…Finally, the molecules are randomly oriented, with the initial intermolecular distance set large enough to make the interaction between them negligible. The vibrational state of the linear CO 2 molecule requires four quantum numbers; however, the one corresponding to the vibrational angular momentum can be disregarded, since bending states with significant rotational energy are unlikely (i. e. the rotational energy with respect the molecular axis is in general very low [54]). The above scheme is suited for VV and VT exchange processes, since cross sections and probabilities obtained from the trajectories are specific for vibrational states, but thermally averaged over rotations (at the given rotational temperature).…”

“…Actually, more refined rate coefficient calculations can be provided by using the forced harmonic oscillator (FHO) theory [49][50][51][52][53] or by using an appropriate potential energy surface (PES) and a quasi-classical trajectory (QCT) dynamic method. The latter approach has been already used for the derivation of some VV and VT transition rates but could be extended also to other transitions [54][55][56], while the FHO theory was used to calculate an extensive matrix of VV and VT transitions for CO 2 very recently [52].…”

Energy transfer dynamics and kinetics of elementary processes (promoted) by gas‐phase CO2‐N2 collisions: Selectivity control by the anisotropy of the interaction

“…The vibrational state of the linear CO 2 molecule is defined by three quantum numbers (see below), since one of them, corresponding to the vibrational angular momentum, is disregarded. This assumption has been discussed and motivated in a series of previous works on CO 2 , [25][26][27] where it was observed that the bending states with high rotational energy are unlikely and the energy associated with the vibrational angular momentum is negligible (see, e.g., Ref. [26], where the time evolution of the radial and angular energy associated with the bending has been considered in typical cases).…”