Investigation of the vibrational relaxation of CO$_2$ molecules in a heterogeneous gas–cluster system

An investigation was made of the relaxation of monomers and clusters of carbon dioxide excited in a glow discharge maintained in a condensing supersonic free jet. Measurements were made of the intensity of the output radiation emitted from the 001 vibrational level of the CO$_2$ molecule in a band at 4.3 $\mu$, and also of the intensity and energy of the molecular beam. It was found that the relaxation of the excited monomers as a result of their collisions with clusters occurred at a rate much higher than the rate of $VT$ relaxation in the gaseous phase, and it increased on increase in the average size of the cluster. The clusters which have received the excitation energy directly from the discharge and indirectly from monomers were found to lose this energy with time: in $\lesssim$1 msec the excitation was converted into heat and this resulted in partial evaporation of the clusters.