Laser catalyzed translational to vibrational energy conversion in CH3F–O2 mixtures

Abstract

Translational energy changes accompanying laser induced V–V equilibration processes in CH3F/O2 and CH3F/Ar mixtures have been studied using the time resolved thermal lensing technique. Enhanced translational cooling in CH3F/O2 mixtures over equivalent CH3F/Ar mixtures was observed. The cooling amplitude varied directly with O2 mole fraction while remaining independent of Ar mole fraction. The above observations suggest strongly the presence of a large endothermic V–V energy transfer pathway in pure CH3F. A knowledge of the CH3F equilibration pathway yields a complete description of the vibrational and translational energy distribution at V–V steady state, and suggests that the ν3 manifold is the predominant reservoir for vibrational energy. In mixtures with a large excess of O2, each absorbed laser photon leads to a vibrational excitation approximately one and one half times the initial photon energy. This vibrational energy increase is brought about by ’’stealing’’ energy from the translational/rotational degrees of freedom. The techniques used here to derive the relative heating and cooling amplitudes for CH3F/O2 mixtures undergoing a specified energy transfer path are general and can be applied to any molecular gas or gas mixture.