Related papers: Water, O2 and Ice in Molecular Clouds
The depth-dependent abundance of both gas-phase and solid-state water within dense, quiescent, molecular clouds is important to both the cloud chemistry and gas cooling. Where water is in the gas phase, it's free to participate in the…
Recent observations with the Submillimeter Wave Astronomy Satellite indicate abundances of gaseous H2O and O2 in dense molecular clouds which are significantly lower than found in standard homogeneous chemistry models. We present here…
We report the results of a large-area study of water vapor along the Orion Molecular Cloud ridge, the purpose of which was to determine the depth-dependent distribution of gas-phase water in dense molecular clouds. We find that the water…
Water (H2O) ice is an important solid constituent of many astrophysical environments. To comprehend the role of such ices in the chemistry and evolution of dense molecular clouds and comets, it is necessary to understand the freeze-out,…
Context: Dark cloud chemical models usually predict large amounts of O2, often above observational limits. Aims: We investigate the reason for this discrepancy from a theoretical point of view, inspired by the studies of Jenkins and Whittet…
Methods: The microscopic equations of H2-formation and protonation are integrated numerically over time in such a manner that the overall structures evolve self-consistently under benign conditions. Results: The equilibrium H2 formation…
We investigate the chemical evolution of a forming molecular cloud behind an interstellar shock wave. We conduct three-dimensional magnetohydrodynamics simulations of the converging flow of atomic gas, including a simple chemical network…
Ultraviolet irradiation of ice is of great interest for understanding the chemistry in both atmospheric and astrophysical environments. In interstellar space, photodissociation of H2O molecules can be a driving force behind the chemistry on…
Molecular oxygen has been the subject of many observational searches as chemical models predicted it to be a reservoir of oxygen. Although it has been detected in two regions of the interstellar medium, its rarity is a challenge for…
We use UV measurements of interstellar CO towards nearby stars to calculate the density in the diffuse molecular clouds containing the molecules responsible for the observed absorption. Chemical models and recent calculations of the…
Absorption of ultraviolet radiation by water ice coating interstellar grains can lead to dissociation and desorption of the ice molecules. These processes are thought to be important in the gas-grain chemistry in molecular clouds and…
The most usual tracer of molecular gas is line emission from CO. However, the reliability of that tracer has long been questioned in environments different from the Milky Way. We study the relationship between H2 and CO abundances using a…
We have constructed three-dimensional models for the equilibrium abundance of molecular hydrogen within diffuse interstellar clouds of arbitrary geometry that are illuminated by ultraviolet radiation. The position-dependent photo-…
The mass of molecular gas in an interstellar cloud is often measured using line emission from low rotational levels of CO, which are sensitive to the CO mass, and then scaling to the assumed molecular hydrogen H_2 mass. However, a…
Context. The chemistry of the diffuse interstellar medium rests upon three pillars: exothermic ion-neutral reactions (" cold chemistry "), endothermic neutral-neutral reactions with significant activation barriers (" warm chemistry "), and…
We model the production of OH+, H2O+, and H3O+ in interstellar clouds, using a steady state photodissociation region code that treats the freeze-out of gas species, grain surface chemistry, and desorption of ices from grains. The code…
We present a detailed model for the thermal balance, chemistry, and radiative transfer within quiescent dense molecular cloud cores that contain a central protostar. Large variations in the gas temperature are expected to affect the…
We present results of classical dynamics calculations, performed to study the photodissociation of water in crystalline and amorphous ice surfaces at a surface temperature of 10 K. Dissociation in the top six monolayers is considered.…
During the evolution of diffuse clouds to molecular clouds, gas-phase molecules freeze out on surfaces of small dust particles to form ices. On dust surfaces, water is the main constituent of the icy mantle in which a complex chemistry is…
The general lack of molecular oxygen in molecular clouds is an outstanding problem in astrochemistry. Extensive searches with SWAS, Odin and Herschel have only produced two detections; upper limits to the O_2 abundance in the remaining…