Probing Molecular Collisions by Raman Spectroscopy

MOLEC 2016, Toledo (Spain), 11 - 16 September 2016Molecular collisions are involved in a number of phenomena in gases: inelastic collisions are responsible for the transport properties and the thermal relaxation in gases, and contribute to the broadening of spectral lines; in turn, cohesive collisions give rise to the formation of molecular clusters. These collisions play an important role in the out-of-equilibrium environment of supersonic gas jets [1], and can be successfully probed by quantitative high-performance Raman spectroscopy with high space (few microns) and time resolution [2]. The experimental setup and methodology developed in our laboratory will be described, and some recent results on inelastic collisions of H2O [3,4] and O2 with He, and of clustering of ortho-D2 [5] will be shown. Rotational populations and number densities, both of isolated molecules or clusters, can be measured along the jet axis with time resolution of nanoseconds. Rotation-translation energy transfer by inelastic collisions can be tracked by means of the time evolution of the rotational populations, and interpreted by using a Master Equation in terms of the state-to-state rate coefficients [3]. The formation of small clusters and their structure can also be tracked with high temporal resolution from the very beginning of condensation (the dimer) [5].This work has been supported by the Spanish Ministerio de Economía y Competitividad (MINECO), grants FIS2013-48275-C2 and CONSOLIDER-ASTROMOL CSD2009-0038.Peer Reviewe