Line-shape parameters and their temperature dependences predicted from molecular dynamics simulations for O2- and air-broadened CO2 lines

Abstract

Requantized classical molecular dynamics simulations (rCMDS) were performed for CO2 highly diluted in O2 at 200, 250, 296 and 350 K using a site-site intermolecular potential. The simulations were made for 0.5 atm of O2 pressure and for a large range of Doppler widths, covering near-Doppler regime to collisional-dominant regime. The Fourier-Laplace transform of the auto-correlation functions of the dipole moment, calculated by rCMDS, leads to the associated spectra of CO2 broadened by O2. Different effects of collisions between CO2 and O2 molecules are included in the simulated spectra. In order to determine the profile parameters of O2-broadened CO2 lines, the rCMDS-calculated spectra were fitted with the speed-dependent Nelkin–Ghatak profile associated with the first-order line mixing. The collisional line broadening coefficient, its speed dependence component, the Dicke narrowing and the first-order line-mixing parameters were retrieved for lines with J up to 50 and for all considered temperatures. The temperature dependences of these line-shape parameters were then deduced using the usual single power law. From results obtained in this work and those obtained for CO2 in N2 [Nguyen et al., J Chem Phys,149, 224301, 2018], the air-broadened line-shape parameters and their temperature dependences for CO2 lines were calculated and compared with literature data showing very good agreement.