Cosmic-ray-induced dissociation and reactions in warm interstellar ices

Abstract

Context. Cosmic ray particles that hit interstellar grains in dark molecular cores may induce whole-grain heating. The high temperature of a CR-heated grain allows energy barriers for bulk diffusion and reactions to be overcome. Additionally, ice molecules are destroyed by direct cosmic-ray induced dissociation. Aims. We provide a justified estimate of the significance of cosmic-ray induced surface-mantle diffusion, chemical reactions in ice, and dissociation of ice species in a star-forming interstellar cloud core. Methods. We considered a gas clump in a collapsing low-mass prestellar core and during the initial stages of protostellar envelope heating with a three-phase chemical kinetics model. The model includes a proper treatment of the stochastic aspect of whole-grain heating and new experimental data for dissociation. Results. We found that the cosmic-ray-induced effects are mostly limited to an increase in abundance for carbon-chain species. The effect on major species abundances is a few percentage points at most. The HNC to HCN ice abundance ratio in ice is increased. Conclusions. Among the processes considered in the model, dissociation is probably the most significant, while diffusion and reactions on warm grains are less important. All three processes facilitate the synthesis of complex molecules, including organic species.

References in corpus (10)

• Complex Chemistry in Star-Forming Regions: An Expanded Gas-Grain Warm-up Chemical Model
• Formation of methyl formate and other organic species in the warm-up phase of hot molecular cores
• Non-thermal desorption from interstellar dust grains via exothermic surface reactions
• Photodesorption of water ice: a molecular dynamics study
• Molecular oxygen in the rho Ophiuchi cloud
• Desorption From Interstellar Ices
• The HNC/HCN Ratio in Star-Forming Regions
• Grain Surface Reactions in Molecular Clouds: The Effect of Cosmic Rays and Quantum Tunneling
• Herschel HIFI observations of O${}_2$ toward Orion: special conditions for shock enhanced emission
• Subsurface chemistry of mantles of interstellar dust grains in dark molecular cores

Cited by in corpus (5)

• Formation of complex organic molecules in hot molecular cores through nondiffusive grain-surface and ice-mantle chemistry
• Chemical Evolution in a Protoplanetary Disk within Planet Carved Gaps and Dust Rings
• Chemical significance of different temperature regimes for cosmic-ray-induced heating of whole interstellar grains
• Evaporative cooling of icy interstellar grains. I. Basic characterization
• The Cosmic-Ray Induced Sputtering Process On Icy Grains