ALBERT

Description: The spectral properties of CO in various ices are presented. Included are peak positions, FWHMs, band profiles, and integrated absorbances of the CO fundamental at 2137/cm in different ices under various conditions. The results reveal that good quality moderate-resolution spectra of the interstellar CO feature can be used to unravel the composition, temperature, and thermal history of interstellar and cometary ices containing CO.

Description: The photochemical and thermal evolution of H2O-, CH3OH-, NH3-, and CO-containing ices whose relative proportions in mixture are consistent with those of interstellar ice are presently studied experimentally. The UV photolysis of these ice analogs invariably generates H2CO, CO2, CO, CH4, and HCO, largely through the photofragmentation of CH3OH. CO and CH4 leave the samples as warmup proceeds to 100 K; most of the parent ice molecules are found to have sublimed upon the reaching of 200 K, with only a mixture of more refractory substances remaining. A residue of CH2 groups remains even after warmup to 300 K.

Description: During the past 15 years considerable progress in observational techniques has been achieved in the middle infrared (5000 to 500 cm(-1), 2 to 20 microns m), the spectral region most diagnostic of molecular vibrations. Spectra of many different astronomical infrared sources, some deeply embedded in dark molecular clouds, are now available. These spectra provide a powerful probe, not only for the identification of interstellar molecules in both the gas solid phases, but also of the physical and chemical conditions which prevail in these two very different domains. By comparing these astronomical spectra with the spectra of laboratory ices one can determine the composition and abundance of the icy materials frozen on the cold (10K) dust grains present in the interior of molecular clouds. These grains and their ice mantles may well be the building blocks from which comets are made. As an illustration of the processes which can take place as an ice is irradiated and subsequently warmed, researchers present the infrared spectra of the mixture H2O:CH3OH:CO:NH3:C6H14 (100:50:10:10:10). Apart from the last species, the ratio of these compounds is representative of the simplest ices found in interstellar clouds. The last component was incorporated into this particular experiment as a tracer of the behavior of a non-aromatic hydrocarbon. The change in the composition that results from ultraviolet photolysis of this ice mixture using a UV lamp to simulate the interstellar radiation field is shown. Photolysis produces CO, CO2, CH4, HCO, H2CO, as well as a family of moderately volatile hydrocarbons. Less volatile carbonaceous materials are also produced. The evolution of the infrared spectrum of the ice as the sample is warmed up to room temperature is illustrated. Researchers believe that the changes are similar to those which occur as ice is ejected from a comet and warmed up by solar radiation. The warm-up sequence shows that the nitrile or iso-nitrile bearing compound produced during photolysis evaporates between 200 and 250K, suggesting that it is carried by a small molecular species. These molecules could be similar to the source material in Comet Halley that is ejected in grains into the coma, freed by sublimation, and photolyzed by solar radiation to produce the observed jets.