Energy mode effectiveness and tunnelling in triatomic reactions: the energy threshold for the Mg+FH→MgF+H reaction

An approximate three-dimensional quantum approach has been adopted to investigate threshold effects for the Mg+FH→MgF+H reaction and their dependence upon reactantsʹ vibrational energy. The main results are: (a) vibrational energy is the most effective mode (however, this switches from vibration at open angles to translation at bent angles); (b) although a fairly heavy atom is transferred, the threshold is determined by the tunneling region, being dominant orientation angles significantly differing from that of the saddle; (c) the threshold moves to lower energy values as the reactant vibrational level increases. A rationale is given in terms of fixed orientation-angle minimum potential-energy profiles.