Bonding in Ion Clusters. I. O4+

Abstract

The O2–O2+ bond energy has been determined to be 0.42 eV from the temperature variation of the equilibrium constant for the reaction: O2+O2+=O4+. The rotational entropy of the O4+ by the ``loose'' cluster model, in which 6 rotational degrees of freedom are assumed, appears to be too large for the observed entropy change, ΔS293°= —20.6 e.u. Approximately half of the bond energy can be ascribed to a simple ion-induced dipole interaction if account is taken of the variation in field strength over the O2 molecule by use of a very simple model. The explanation for the residual bond energy discrepancy might be that the polarizability of O2 is larger than the low-field experimental value at high field strengths such as those ∼3 Å from an ion. The experimental method described is of wide applicability in determining bond energies in ion clusters.