The [H-2, C, N, O](+) potential energy surface (PES) in its triplet state multiplicity has been explored by means of high-level ab initio calculations, carried out in the framework of the G2 theory. From the PES survey we conclude that some of the products of the N+(P-3) + H2CO reaction are the result of a competitive dissociation of the H2CON+ cation into NO+ + H2C or N + H2CO+. Although the first process is moro exothermic than the second one, it involves a conical intersection, and as a consequence N + H2CO+ are the dominant products. NH + HCO+, which are also experimentally observed products, can be formed either by the dissociation of the HCONH+ cation, through another conical intersection, or by the fragmentation of a quite stable HN . . . HCO+ complex. Other possible products, such as CNH + OH+, HCN + OH+, and CO + NH2+, although exothermic, should not be observed since the corresponding reaction pathways involve high activation barriers. These conclusions are in good agreement with the experimental evidence. The topology of the [H-2, C, N, O](+) PES also explains why no reaction is observed when NH2+ and CO or CH2 and NO+ interact in the gas phase, while in CH2+ + NO reactions, only the charge exchange channel is open. We also predict that the dominant products in OH+ + HCN reactions should be NH + HCO+. However, when this reaction involves the CNH isomer the observed products should be not only NH + HCO+ but also NH2+ + CO.