Molecular processes in interstellar clouds

Ronald McCarroll

Laboratoire de Chimie Physique (UMR 7614 du CNRS), Université Pierre et
Marie Curie, Paris, Francia

Interstellar space is filled with a very dilute gas in which new stars and planets can form. Despite the exceedingly low temperatures and densities of interstellar clouds, more than 150 different molecules have been observed indicating a rich and interesting chemistry. The relative abundance of these molecules is governed by the kinetics of the elementary atomic and molecular processes. Both gas phase processes (ion-molecule reactions, photodissociation, dissociative recombination, radiative association,…) and the formation of molecules on the surfaces of icy interstellar grains are of importance. But prior to 1990, the absence of experimental measurements at low temperatures, there was little incentive to develop theoretical models. Since then, the development of supersonic jets have made it possible to study reactive systems in the laboratory at temperatures as low as 10-20K. On the theoretical side, the development of large scale quantum mechanical methods on some simple systems has led to many quantitative results which clarify the main issues.
In this talk, I shall be concerned with some applications of the statistical theory of chemical reactions, which was originally developed by J.C. Light in 1967 and W.H Miller in 1970 but never hitherto applied at low temperatures. Some recent results on H+-H2, H+-D2, D+-HD, CH+-H, S-H2, N-OH will be presented for which it is possible to make detailed comparisons either with the best quantum calculations and/or with experiment. The validity of the statistical model is shown to be very satisfactory.

Este coloquio se llevará a cabo el Viernes 23/11 a las 15hs en del edificio del IAFE, Ciudad Universitaria.