Desorption of large molecules from grains in dense interstellar clouds

Results are reported from laboratory studies tracing the nondestructive desorption of whole leucine (131 amu) molecules from surfaces induced by fast, heavy-ion bombardment. It is proposed that heavy ions in the cosmic-ray flux may induce desorption of large molecules from the surfaces of grains in molecular interstellar space. Cosmic-ray protons and UV light produced by cosmic rays can process grain mantles in interstellar 'molecular clouds'. This processing creates bonding among small molecules on grains which can produce larger molecules. The less frequent heavy nuclei bombardment can cause the evaporation of small molecules. It is shown that the heavy nuclei can also impulsively eject intact much larger molecular species. It is pointed out that since molecules with masses of about 100 amu are known to exist in molecular clouds and are either formed on or eventually condense onto the grain surfaces, heavy cosmic-ray nuclei may cause desorption of such molecules from the grain surfaces.