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

Abstract

An experiment has been constructed to determine the rovibrational states populated in the formation of H2 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 H2 molecules desorbing from the cosmic dust targets to be determined providing information on the energy budget of the H2 formation process in the ISM. Preliminary results from the experiment, to prove its viability, show that H2 molecules formed on an highly oriented pyrolytic graphite surface have a measurable population of excited vibrational and rotational states.