MECHANISMS FOR THE REACTION OF TRIPLEX P- FORMATION OF THE P-X BOND( WITH XH (X=CL, F) )

Ab initio molecular orbital calculations on the ion-molecule reactions of the tripler P+ with ClH and FH have been performed at the G1, G2* (G1 and G2 methodologies with MP2/6-31G(d,p) base geometries), MCSCF, and QCISD(T) levels of theory. Two reaction mechanisms leading to PX( +) + H (X = Cl, F) products have been investigated. Both of them proce ed through the formation of an ion-molecule complex, in the first step of the reaction, without energy barrier. Reaction pathway I involves the abstraction of hydrogen from the X atom. A significant configurati on mixing is found to take place for this abstaction, and we have foun d that it is energetically unfavored with respect to the reactants. Re action pathway II consists of the transposition of the hydrogen from t he X atom to P, to form the HPX(+) intermediate, and then abstraction of the hydrogen from P. Reaction pathway II, which is energetically mo re favorable than pathway I, could be a likely source of P-Cl (X = F, Cl) bond containing compounds in the interstellar medial however, it i s predicted to be an unlikely source for P-F compounds.