An apparatus to determine the rovibrational distribution of molecular hydrogen formed by the heterogeneous recombination of H atoms on cosmic dust analogues

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.