Quantum-chemical model evaluations of thermodynamics and kinetics of oxygen atom additions to narrow nanotubes.

This paper reports a computational study of oxygen additions to narrow nanotubes, a problem frequently studied with fullerenes. In fact, fullerene oxides were the first observed fullerene derivatives, and they have naturally attracted the attention of both experiment and theory. C60O had represented a long-standing case of experiment-theory disagreement, and there has been a similar problem with C60O2. The disagreement has been explained by kinetic rather than thermodynamic control. In this paper a similar computational approach is applied to narrow nanotubes. Recently, very narrow nanotubes have been observed with a diameter of 5 A and even with a diameter of 4 A. It has been supposed that the narrow nanotubes are closed by fragments of small fullerenes like C36 or C20. In this report we perform calculations for oxygen additions to such model nanotubes capped by fragments of D2d C36, D4d C32, and Ih C20 fullerenic cages (though the computational models have to be rather short). The three models have the following carbon contents: C84, C80, and C80. Both thermodynamic enthalpy changes and kinetic activation barriers for oxygen addition to six selected bonds are computed and analyzed. The lowest isomer (thermodynamically the most stable) is never of the 6/6 type, that is, the enthalpically favored structures are produced by oxygen additions to the nanotube tips. Interestingly enough, the lowest energy isomer has, for the D2d C36 and D4d C32 cases, the lowest kinetic activation barrier as well.