Journal of Physical Chemistry, Vol.100, No.35, 14643-14650, 1996
Theoretical-Studies of Possible Processes for the Interstellar Production of Phosphorus-Compounds - The Reaction of P+ with C3H2
An ab initio study of the (PC3H)(+) and (PC3H2)(+) species was carried out. Geometries for the different isomers are reported at the MP2/6-31G* level, whereas relative energies were computed at the MP4/6-311G** level. Our calculations predict that the global minimum of the (PC3H)+ system is a linear isomer (?IT electronic state), followed in stability order by a rhomboidal structure (B-2(1) electronic state) which lies about 15.8 kcal/mol higher in energy. We predict very high proton affinities for linear C3P and rhomboidal C3P : 222.4 and 220 kcal/mol, respectively. The lowest-lying (PC3H2)(+) tripler state is a three-membered ring, (3)A(2) electronic state, which can be viewed as the ion-molecule complex formed by the interaction of P+ with the unique carbon atom of cyclopropenylidene (c-C3H2). The species formed by the interaction of P+ with vinylidene-carbene (1-C3H2) lies only 9 kcal/mol higher in energy, In the case of the reaction of P+ with c-C3H2 charge transfer is a competitive process. In fact, since the ionization potential of c-C3H2 is lower than that of phosphorus, the reaction in the interstellar medium is more likely to be initiated by P + c-C3H2+. In that case, only production of a four-membered ring PC3H+ species should be feasible, since it is an exothermic and barrier-free process. For the reaction of P+ with 1-C3H2 the production of linear PC3H+ is exothermic by 62 kcal/mol, whereas formation of a three-membered ring PC3H+ species with an exocyclic carbon is exothermic by about 11.5 kcal/mol. Both processes seem to proceed without activation barrier. Therefore, the reactions of P with c-C3H2+ and of P+ with 1-C3H2 are feasible in the interstellar medium and consequently possible sources of precursors of C3P in space.
Keywords:PLESSET PERTURBATION-THEORY;MOLECULAR-ORBITAL METHODS;CARBON-CHAIN MOLECULE;ASTRONOMICAL IDENTIFICATION;LABORATORY DETECTION;BASIS SET;CLOUDS;ENERGY;IONS;CYCLOPROPENYLIDENE