Ab initio study of the thermodynamic and kinetic stability of the ammonium radical

• Published in: Chemical physics 1983-06, Vol.77 (2), p.287-299
• Main Authors: Cardy, H., Liotard, D., Dargelos, A., Poquet, E.
• Format: Article
• Language: English
• ISSN: 0301-0104
• DOI: 10.1016/0301-0104(83)85086-1

An increasing interest in the possible existence of the NH 4 radical has emerged in recent years. In this paper we report an ab initio UHF CI study of the ammonium radical, an investigation of parts of the energy surface around NH 4 and a theoretical prediction of the kinetic parameters of the radical formation and dissociation reactions within the framework of the TST theory. The ground state of the ammonium radical appears to be of the Rydberg type. Its ionization potential is found to be 4.29 eV. The NH 4 formation reaction from NH 2 + H 2 is very slightly exothermic whereas the reaction from NH 3 + H is slightly endothermic. We find a transition state of C 3 v symmetry for the dissociation of NH 4 into NH 3 + H. The insertion of H 2 into NH 2 occurs according to a two-step mechanism whose determining step corresponds to the crossing of a saddle point with C s symmetry previously obtained in the study of the reaction NH 2 + H 2 → NH 3 + H. Finally, we predict for NH 4 and ND 4 lifetimes of 0.1 and 1.4 μs respectively.