High Fidelity Modeling of Thermal Relaxation and Dissociation of Oxygen

Abstract

The rovibrational relaxation of oxygen in a heat bath of parent atoms is studied by means of master equations. It is found that vibrational and rotational relaxation times exhibit a pattern inherent in a chemically reactive collisional pair. An intrinsic feature of the O3 molecular system with a large attractive potential is a weak temperature dependence of the rovibrational transition rates. For this reason, the quasi-steady vibrational and rotational temperatures experience a maximum at increasing translational temperature. The average loss of internal energy due to dissociation quickly diminishes at high temperatures, compared to other molecular systems. The present quasi-steady dissociation rate coefficients are utilized to validate the accuracy of the multi-temperature model.

Simulation of O2-N Collisions on ab-initio Potential Energy Surfaces

“…However, at temperatures above 5000 K the relaxation via the 4A PES becomes more efficient than via the 2A PES. A similar effect was observed when relaxation in oxygen occurs via O 2 -O and O 2 -O 2 channels simultaneously [21]. In that case, the repulsive interaction in pure O 2 is more efficient for vibrational thermalization at temperatures above 10,000 K, compared to the relaxation via the O 3 complex.…”

“…At higher temperatures, however, there are some apparent differences. While the QSS vibrational temperature increases monotonically for collisions that proceed on the 4A PES, the quasi-stationary T vib for the 2A PES experiences a maximum at T=16,000 K. A similar effect was observed for O 2 state-resolved relaxation in collisions with parent atom [21]. In the O 2 -O interaction, the atom-molecular collisions proceed on a barrierless PES that has a minimum of O 3 metastable formation.…”

“…Among the considered projectiles, the O 2 -O interaction has the smallest coupling coefficient C vib and the most rapid decrease of C vib with temperature. As discussed previously [21], this is the effect of the barrierless potential energy surface. Dissociation rate coefficient in O 2 -O collisions rapidly increases with translational temperature, while the vibrational relaxation time has a weak temperature dependence.…”

“…The O 2 -N, O 2 -Ar and O 2 -O systems are shown with solid, dashed and dashed-dotted lines, respectively. The O 2 -O data [21] represents the energy loss coefficients in the presence of a strongly attractive, barrierless potential [27]. On the contrary, the O 2 -Ar data [22] is obtained assuming a purely repulsive Buckingham potential [28].…”

High fidelity modeling of thermal relaxation and dissociation of oxygen

“…The global recombination rate coefficient, R , is estimated from D via the principle of detailed balance. Vibrational energy coupling coefficient corresponds to the loss of internal energy in O 2 -O collisions in the presence of rotational equilibrium [59].…”