Modeling the Evolution of Cold Cloud Interstellar Dust-Grain Ices

Astronomy and Astrophysics – Astronomy

Scientific paper

Rate now

  [ 0.00 ] – not rated yet Voters 0   Comments 0

Details

Scientific paper

We investigate the formation and evolution of interstellar dust-grain ices under cold cloud conditions, with a particular emphasis on CO2. We use a three-phase model (gas/surface/mantle) to simulate the coupled gas--grain chemistry, allowing the distinction of the chemically-active surface from the ice layers preserved in the mantle beneath. We undertake to treat more accurately the quantum-tunneling rates of barrier-mediated surface reactions, and we explicitly consider competition between such reaction rates and thermal hopping processes. These models show excellent agreement with the observed behavior of CO and CO2 ice in the interstellar medium. The observed threshold between regimes in which CO2 or CO is the dominant ice constituent after H2O is found to be caused ultimately by the near-complete gas-phase conversion of atomic carbon to CO, which is itself determined by CO and H2 self-shielding. The change in the availability of gas-phase carbon alters the balance of the grain-surface chemistry, leading to a sharp change-over in the dominance of CO2/CO. The most probable grain-surface production mechanism for CO2 is the formation of a loosely-bound O...CO complex, whose oxygen atom is easily hydrogenated, leaving a highly excited complex which quickly overcomes an activation energy barrier to form CO2 + H.

No associations

LandOfFree

Say what you really think

Search LandOfFree.com for scientists and scientific papers. Rate them and share your experience with other people.

Rating

Modeling the Evolution of Cold Cloud Interstellar Dust-Grain Ices does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.

If you have personal experience with Modeling the Evolution of Cold Cloud Interstellar Dust-Grain Ices, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Modeling the Evolution of Cold Cloud Interstellar Dust-Grain Ices will most certainly appreciate the feedback.

Rate now

     

Profile ID: LFWR-SCP-O-1399472

  Search
All data on this website is collected from public sources. Our data reflects the most accurate information available at the time of publication.