Detection of large interstellar molecules with radio interferometers

摘要

More than 112 interstellar molecular species have been reported to date. Small interstellar molecules and large interstellar molecules with a low degree of saturation (low hydrogen count) can be formed in quiescent gas clouds or in shock fronts by gas-phase chemical reactions, such as ion- molecule reactions and neutral-neutral reactions. Because these gas-phase species are found in spatially extended clouds, they have dominated most of the past single-element telescope studies of extended interstellar molecular clouds. Now, with the advent of radio interferometric arrays that operate at millimeter wavelengths with high spatial resolution, the study of a rich dust-phase chemistry around small hot molecular cloud cores has become possible. These small cloud cores, less than 0.1 parsec in diameter, form the type of dusty environment that contains presolar nebulae contracting under gravity before the onset of fusion; they contain large, complex, interstellar molecules with a high degree of saturation that are also of some biological interest: acetone, ethyl cyanide, ethanol, acetic acid, and probably the smallest amino acid, glycine. These molecules cannot be formed easily by gas-phase reactions alone; consequently, theories of solid state chemical reactions on grain surface ice mantles are often invoked to form these large molecules and evaporation is proposed as the mechanism that drives them into the gas phase. Hence, high resolution millimeter-wavelength arrays can spectroscopically sample the composition of evaporated presolar material--the material that eventually may form the basis for a type of prebiotic organic chemistry similar to that found on the early Earth.