Vibrational relaxation and triggering of the non-equilibrium vibrational decomposition of CO2in gas discharges

Non-equilibrium vibrational dissociation CO2 → CO + O at translational-rotational temperatures T ≤ 1200 K is investigated with semi-empiric and computational models. The governing parameter Q/n02 has been introduced, where Q is the specific volumetric power coupled into vibrational states and n 0 is the initial number density of CO2. It has been shown that the non-equilibrium vibrational process can only be triggered when Q/n02 exceeds some critical value determined by the speed of vibrational relaxation. Simple semi-empiric calculations are backed by the state-to-state simulations of the CO2 vibrational kinetics in two-modes approximation performed for conditions of microwave sustained gas discharges. The vibrational kinetics model is benchmarked against the experimental vibrational relaxation times as well as the shock tube data on the rate of the process CO2 + M → CO + O + M for M = Ar and literature data for M = CO2. At T = 300 K the estimated Q/n02crit ≃ 6×10-40 W m3 or Q/p2crit ≃ 35 W (m-3 Pa-2) (p is the gas pressure). Q/p2crit is found to always increase with increased T. © 2022 The Author(s). Published by IOP Publishing Ltd.