Observed visual magnitudes of the short‐period comets 2P/Encke, 81P/Wild 2, 6P/d'Arrest and 73P/Schwassmann–Wachmann 3 and the long‐period comet C/1984 V1 Levy–Rudenko are converted into water release rates. These H2O release rates are used to derive the nuclear surface areas, minimum nuclear radii and gas mass loss of these comets. Combined with estimated gas release rates, we make an uniform and systematic analysis of the observed continuum fluxes in the comae of these comets with the objective to find dust release rates, effective dust particle sizes and total mass release rates. The nuclei of Comets 2P/Encke, 6P/d'Arrest and 73P/Schwassmann–Wachmann 3, which has split into as many as four fragments, are potential targets for the flyby of the CONTOUR (COmet Nucleus TOUR) spacecraft, scheduled for launch in 2002 July, while Comet 81P/Wild 2 has been chosen as a target by the NASA spacecraft STARDUST, which was launched on 1999 February 7.

Glycine (C 2 H 5 NO 2) was the first amino acid to be detected in space by the stardust space probe in Comet Wild2, and is used by living organisms to make proteins. We discuss three different reaction paths for the formation of glycine in interstellar space from some simpler molecules detected in the interstellar medium. The possibility of the formation of glycine in interstellar space is considered by radicalradical and radical-molecule interaction schemes using quantum chemical calculations with density functional theory at the B3LYP/6-31G (d,p) level. In the chemical pathways we discuss, a few reactions are found to be totally exothermic and barrierless while others are endothermic with a very small reaction barrier, thus giving rise to a high probability of forming glycine in interstellar space.

No abstract

Recently a new molecule, cyanomethamine, has been detected towards Sagittarius B2(N) (Sgr B2(N)). Studying the formation mechanisms of complex interstellar molecules is difficult. Hence, a theoretical quantum chemical approach for analyzing the reaction mechanism describing the formation of interstellar cyanomethamine through detected interstellar molecules and radicals (NCCN+H) is discussed in the present work. Calculations are performed by using quantum chemical techniques, such as Density Functional Theory (DFT) and Møller-Plesset perturbation (MP2) theory with a 6-311G(d,p) basis set, both in the gas phase and in icy grains. The proposed reaction path (NCCN+H+H) has exothermicity with no barrier which indicates the possibility of cyanomethamine formation in the interstellar medium.

Radical-radical and radical-neutral interaction schemes are very important for the formation of comparatively complex molecules in low-temperature chemistry. The formation of amino acids, such as serine, in the interstellar medium is quite difficult. We explored the possibility of serine formation in the interstellar medium through detected interstellar molecules such as CH, CO, and OH by radicalradical and radical-neutral interactions in the gaseous phase using rigorous quantum-chemical calculations. The reaction energies, the low potential barrier and the structures of all the geometries involved in the reaction path show that serine formation is possible in interstellar space via the reaction paths.