The prediction of isomers for phosphorus clusters P8 and P9+

In the study of cationic phosphorus clusters produced in direct laser vaporization, it has been realized that P-8 and P-9(+) are entities to be considered in mass spectrum interpretation. We acquired 20 P-8 and 19 P-9(+) isomers with molecular graphics and then carried out optimizations with molecular mechanics, PM3 semi-empirical and ADF density functional calculations. In these isomers, the phosphorus atoms adopt twofold, threefold or fourfold coordination. According to the bonding energies, the cage-shape models are more stable than the planar ones, and the models with a large planar ring are the least stable. The most stable cuneane P-8 structure with 12 single bonds was adopted as the basic unit for polymerization. By adding a phosphorus atom to the bottom right side of cuneane and assuming a positive charge for optimization, we derived P-9(+) isomers and identified the one with the lowest bonding energy, We detected that the P-9(+) isomers with double bonds are less stable and the distortion of P-9(+) somers with high symmetry would result in lower bonding energies. (C) 2000 Elsevier Science B.V. All rights reserved.