High-level ab initio calculations in the framework of the G2 theory have been performed for the [H3, P, F]+ singlet- and triplet-state cations. The bonding characteristics of singlet- and triplet-state cations are rather different. The latter are weakly bound species involving electrostatic and/or polarization interactions, while the former present covalent bonds. As a consequence, while in the F+(3P) + PH3(1A1) reactions in the gas phase the charge-transfer process competes with the formation of HF(1Σ+) + PH2 +(3B1), the main products when the reaction involves the F+ cation in its 1D first excited state are HF(1Σ+) + PH2 +(1A1). In both cases, the reactions are extremely exothermic, and therefore, the products are anticipated to be vibrationally excited. The [H3, P, F]+ triplet-state cations are good examples of molecular planetary systems, in which a neutral fluorine atom or a neutral HF molecule orbits around a PH3 + or a PH2 + moiety, respectively. Although the singlet PES lies systematically below the triplet PES, there are regions where both surfaces approach each other significantly. The spin−orbit coupling between them, evaluated at the corresponding minimum energy crossing point, indicates that a fast transition between both PESs should take place, implying the possibility of having “spin-forbidden” reactions. From our calculations, the heat of formation for FPH2 was estimated to be −58.2 ± 2.5 kcal/mol.