J. Phys. Chem. 1994,98, 3985-3988
3985
Theoretical Study of the C2P Radical and (C,P)+Species A. Largo’ and C. Barrientos Departamento de Quimica Fisica y Analitica, Facultad de Quimica, Universidad de Ooiedo, 33006 Oviedo, Spain
X. L6pez and J. M. Ugalde’ Kimika Fakultatea, Euskal Herriko Unibertsitatea, P.K. 1072, 20080 Donostia. Euskadi, Spain Received: November 18, 1993”
An ab initio molecular orbital study has been carried out for the C2P radical, a molecule which could be of astrophysical interest, on the doublet and quartet surfaces. Geometries have been obtained at the MP2/6-3 l G * level, whereas M P 4 theory has been employed to compute electronic energies. We have found that the C P C isomer lies quite high in energy, but there are two states quite close in energy: linear C C P (211state) and cyclic C2P (2B2 state). We predict linear C C P to be the ground state, but with cyclic C2P lying just about 6 kcal/mol above. These two states are predicted to have high dipole moments, 3.293 and 2.535 D, respectively. Harmonic vibrational frequencies and infrared intensities have also been estimated. In the case of the cation, we have found that linear CCP+ is also the ground state whereas the energy difference with the cyclic Cb symmetric state is now higher than in the case of the neutral system, about 15 kcal/mol. Introduction In recent years there has been a growing interest in the interstellar chemistry of second-row elements. The synthesis of phosphorus-containing compounds is especially interesting after the detection of PN1p2and PC3 in space. A number of papers have addressed the phosphorus chemistry in the interstellar medium,” and several experimental works have focused on ionmolecule reactions of PH,+ ions.8~~ Other works have dealt with theoretical studies of possible processes for interstellar production of phosphorus compounds.10-14 One of the most important results of the study of Millar? using the laboratory data of Smith et al.9 is that phosphorus-carbon molecules such as C2P and HC2P might be detectable in warm dense clouds, provided they are unreactive with oxygen atoms. Since the molecular structure of C2P is so far unknown, we have decided to carry out a theoretical study on this species. In addition to its possible astrophysical significance, the C2P radical is of interest in its own right. CzP is isovalent with C2N, a molecule with two different isomers, corresponding to the connectivities CNC and CCN, which have been studied both experimentallyl”19 and theoreti~ally.~O-~~ In the case of the nitrogen-containing molecule, the CNC isomer is found to be the ground state. For the phosphorus compound one should not expect linear CPC to be more stable than PCC since a setup with a carbon-carbon multiple bond and a P-C bond should be more stable than two P-C bonds (although with a somewhat multiple character). However, one could think that with a second-row element a possible cyclic structure could be competitive, as in the case of silicon dicarbide where a C2, cyclic isomer was found to be the ground ~ t a t e . * ~In
