Journal of Molecular Structure (Theochem), 166 (1988) 409-414 409 Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands A THEORETICAL STUDYOF THE REACTIONOF Fe + (6D) WITH H 2 M. Sodupe, A. Prenafeta, J.M. Lluch, A. Oliva and J. BertrAn Departament de Quimica. Universitat AutSnoma de Barcelona 08193 Bellaterra (Barcelona,, Spain SUMMARY An ab~ initio t h~.oretical study of the reaction Fe + (6D) + H~(l~--~) - ~FeH*(°~) + H(S) has been carried out with the UHF method u~ing the Huzinaga's MINI-2 basis set. The obtained results show that the Fe ground state reacts v~ry inefficiently, since the reaction is highly_~ndothermic (64.5 kcal mol" ) and presents an energy barrier of ll.5 kcal mol - in excess of its endothermicity. INTRODUCTION The activation of molecular hydrogen by transition metals is important to understand a variety of homogeneous and heterogeneous catalytic processes. Because of this much experimental effort has been devoted to the study of the gas-phase reaction M + + H2-~MH+ + H and its isotopic analogues (I-7). Until the last years, specific information regarding the individual reactivi- ties of the different electronic states of the reactant metal ion was lacking since it is a very difficult experimental problem to identify and control the population of these states. Recently, this information has been obtained by Elkind and Armentrout (6,7) for the first-row transition metals. They have shown that the reactivity is very sensitive to the electronic configuration and spin state of the metal. An interesting case is the reaction of Fe + with H2, the reactivity of Fe + having been generally attributed to its 6D(4s3d6) ground state. Elkind and Armentrout have shown that the 4F(3d7) first excited state, which is only 0.25 eV above the ground state, is much more reactive than the 6D state and that it react via a FeH2 + intermediate. On the contrary the less reactive may ground state is shown to prefer a collinear approach, the threshold energy being 2.35 eV. (6). From this value, the bond dissociation energy of FeH + has been determined with the assumption that there exists no barrier to reaction in excess of the endothermicity. 0166-1280/88/$03.50 © 1988Elsevier Science Pub~shers B.V.