ON A POSSIBLE MECHANISM FOR AR-4(+) FRAGMENTATION

The full potential energy surface (PES) for the collinear Ar-4(+) clus ter as a function of the three internuclear distances is computed at t he post-Hartree-Fock level using Density Functional Theory (DFT) metho ds to treat dynamic correlation effects. The behaviour of the overall configuration energy minima as the central Ar-2(+) bond stretches is a nalysed as a function of the fragmentation coordinates of the wing ato ms. The coupling between the stretching coordinate and the fragmentati on coordinates is also analysed over the whole PES. The calculations s uggest that large vibrational energy content in the core dimer ion cau ses localization of the coupling with either wing atoms which could in turn favour energetically the sequential fragmentation, while Ar-4(+) with a vibrationally cold core markedly lowers any energy barrier to fragment in a concerted fashion. Such suggestions provide further usef ul information for what has been found in some of the experimental stu dies on this ionic system (and on larger ionized argon clusters) and u nderline the possible role which the internal vibrational energy conte nt of the ionic cluster can play in the fragmentation.