Theoretical study of possible ion-molecule reactions leading to precursors of glycine in the interstellar medium

摘要

Several ion-molecule reactions that could lead to precursors of interstellar glycine have been theoretically studied. Predictions for their reaction enthalpies have been carried out at the B3LYP (Becke's three-parameter exchange functional and the gradient-corrected functional of Lee, Yang, and Parr) QCISD(T) (quadratic configuration interaction method with singles and doubles substitutions followed by a perturbative treatment of triple substitutions), and MP4 (fourth-order Moller-Plesset perturbation theory including single, double, triple, and quadruple substitution) levels of theory. The reactions of protonated aminomethanol with formic acid and of HCO2+ with methylamine are clearly endothermic and therefore not likely to be feasible under interstellar conditions. On the other hand, different reactions of cationic derivatives of ammonia with acetic acid or the reaction of CH3NH2+ with formic acid are clearly exothermic. One of the most promising processes, based on its exothermicity (about 27 kcal/mol), is the reaction of NH2+ with CH,COOH. (C) 2004 Wiley Periodicals, Inc.