Measurement of the Kinetic Energy of Hydrogen Molecules Desorbing from Amorphous Water Ice

Abstract

A hydrogen molecule that is formed on an interstellar grain might retain some of the 4.48 eV of energy that is released in the recombination reaction of two hydrogen atoms. We set up an experiment to measure the translational (kinetic) energy of hydrogen molecules after they are formed on and are ejected from the surface of an interstellar dust grain analog. Here we report the first measurements of the kinetic energy of molecular deuterium as it leaves the surface of an amorphous water sample. The astrophysical implications of such measurements are discussed.