Laboratory Astrophysics of Interstellar Ice Mantles

University Of Virginia Main Campus, Charlottesville VA

Investigators

Abstract

AWARD NO: AST - 0807832 INSTITUTION: University of Virginia Main Campus PI: Raul A Baragiola TITLE: Laboratory Astrophysics of Interstellar Ice Mantles This research will address the question of the balance between molecules in the gas and on dust grains in dark interstellar molecular clouds, one of the central unsolved problems in the evolution of interstellar matter. The problem consists of the following: due to the low temperature of molecular clouds and high condensation coefficients, all gaseous species, with the exception of H2 and He would be depleted by condensation on grains, in times of typically 100,000 years. Yet a typical molecular cloud lives much longer, millions of years, and contains a relatively high number of molecules in the gas phase. Therefore, an efficient desorption mechanisms must operate. However, none of the proposed mechanisms can convincingly maintain the gas population observed. For this reason, the laboratory studies to be undertaken here perform novel experiments to determine desorption rates due to: a) photodesorption by ultraviolet Lyman-alpha photons, b) thermal desorption by recombination of H atoms into H2 molecules adsorbed on ices, c) desorption from dissociative electron attachment caused by low energy electrons. In addition, since the main interstellar gas in molecular clouds is molecular hydrogen, which can be readily absorbed in microporous water ice, the experiments will simulate those conditions, studying H2 adsorption, replacement of H2 by adsorption of other gases such as CO, and the effect of adsorbed hydrogen on the photodesorption and molecular photosynthesis in water ice. The research will use highly sensitive techniques of microgravimetry and mass spectrometry to measure desorption of ices at cryogenic temperatures in ultrahigh vacuum. The research group has demonstrated expertise in the research area and promote innovation by applying knowledge and techniques from other areas of science into astronomical problems, such as the new concept that desorption by low energy electrons will occur in molecular clouds. In addition to the astronomical applications of the research, the understanding of radiation processing of materials developed here has applications in semiconductor, thin film and chemical industries. The Dr. Baragiola is collaborating with scientists on some of these applications. Students will be active participants in this research which will provide training for students that will prepare them for industrial, government and academic career paths. Some of the research will also be incorporated into undergraduate introductory astronomy courses in part to help students understand the role laboratory astrophysics plays in our ongoing quest to understand our universe.