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An experiment has been constructed to determine the rovibrational states populated in the formation of H 2 on the surface of cosmic dust under conditions approaching those of the interstellar medium (ISM). During the experiment, a beam of atomic hydrogen of controlled temperature is incident upon a target which is an analogue of cosmic dust. Molecular hydrogen desorbing from the target's surface is ionized using (2 + 1) resonance enhanced multiphoton ionization and detected using time-of-flight mass spectrometry. The experiment allows the rovibrational populations of the H 2 molecules desorbing from the cosmic dust targets to be determined providing information on the energy budget of the H 2 formation process in the ISM. Preliminary results from the experiment, to prove its viability, show that H 2 molecules formed on an highly oriented pyrolytic graphite surface have a measurable population of excited vibrational and rotational states.

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The ionic products formed in collisions between and have been detected and identiÐed as a CF 2 2`NH 3 function of the centre-of-mass collision energy (0.5È4 eV). Electron-transfer reactivity is found to be responsible for the major proportion of these product ions CF`, and C`) and their relative (CF 2 `, N H 3 `, NH 2 ìntensities can be rationalised by the use of LandauÈZener theory. This analysis indicates, in common with previous studies, that beams contain ions in more than one long-lived electronic state. In addition to CF 2 2è lectron-transfer reactivity, a bond-forming reaction producing HNCF`is also detected and isotopic labelling conÐrms that this weak product ion signal is indeed a result of collisions between and The CF 2 2`NH 3 . variation in the HNCF`ion yield as a function of collision energy suggests that this bond-forming reaction proceeds via a di †erent mechanism to the previously investigated " chemical Ï reaction between and CF 2 2`D 2 .

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