Jan HRUSAK (J. Heyrovsky Inst. Phys. Chem. and IMS), Detlef SCHRODER (Tech. Univ. Berlin), Helmut SCHWARZ (Tech. Univ. Berlin) and Suehiro IWATA
[Bull. Chem. Soc. Jpn. 70, 777 (1997)]
The neutral and the lowest cationic (singlet and triplet) potential-energy surfaces (PES) of [Si,P,H2] have been explored by means of ab initio MO calculations at the G2 level of theory as well as the hybrid DFT (B3LYP/6-311G**) method. Contrary to the neutral and triplet surfaces, where the H2SiP+/0 isomers represent the global minima, for the singlet cation a doubly bridged P(H)2Si+ structure has been identified as the most stable isomer with the non-bridged H2SiP+ species being significantly less stable ((DELTA)E = 31.7 kcal/mol at G2). As far as the comparison of the two quantum-chemical methods (i.e. G2 and B3LYP) is concerned, the calculated relative energies DE are quite close to each other with deviations smaller than 4 kcal/mol. However, while the non-bridged SiPH2+ (1A') represents a minimum at the G2 level, it could not be located using the hybrid DFT method. The computationally predicted singlet and triplet [Si,P,H2]+ potential-energy surfaces provide insight into the course of the ion/molecule reactions of Si+¥ with phosphine and P+ with silane, respectively, which were examined experimentally. Thus, the reaction of the doublet species Si+¥ with phosphine allows access to the non-classical, bridged P(H)2Si+ structure, while in the reaction of the P+ triplet cation with silane, no evidence for Si-P bond formation is obtained.