Techniques for the study of reaction kinetics at low temperatures: application to the atmospheric chemistry of Titan

Data on the low-temperature (< 200 K) dependence of the kinetics of chemical reactions are of great importance for understanding the composition of planetary atmospheres (as well as interstellar clouds). To date such studies have been relatively rare but the situation is beginning to change. During the past 10 years a number of experimental instruments have been designed to address this problem. These instruments rely on either cryogenic or supersonic cooling, and both methods have been applied to the study of neutral-neutral or ion-neutral reactions. We briefly review these different techniques, with an emphasis on the CRESU method, and provide examples of the types of reactive systems that have been studied, with particular attention to those relevant to the atmosphere of Titan. The perspectives for future work are also evoked.