Molecular synthesis in interstellar clouds - Some relevant laboratory measurements

Data are presented which have resulted from a systematic program of measurements of the reaction rate coefficients and product distributions of positive ion/molecule reactions which are probably important reaction channels for the synthesis of molecular species observed in interstellar gas clouds. In particular, the reactions of the CHn(+) and C2Hn(+) ions (n = 0 to 4) with several molecules have received special attention, and several likely channels for the synthesis of observed interstellar species have been identified. Special consideration is given to the few reactions which proceed via rapid three-body association in the laboratory experiments, since it is suggested that these association reactions may proceed at significant two-body rates which involve radiative stabilization in low-pressure interstellar clouds. This mechanism can thus result in the formation of a relatively large molecule in a single interaction. These ideas are utilized to explain tentatively the relative abundances of some hydrogen-carbon-nitrogen molecules in Ori A and Sgr B2.