  Reductive hydrogenation was applied to two types of single-walled carbon
nanotubes with different diameter range. Alkali metal intercalation, followed
by reaction with methanol, led to hydrogenated products. Both yield and
selectivity of this reaction showed strong dependence on diameter, contrary to
expectation based on simple curvature effects. The observed yield, as detected
by thermogravimetry-mass spectroscopy and 1H-NMR, is drastically reduced in
small-diameter tubes where the alkali dopant does not reach the inside of the
bundles. Wide range optical transmission measurements were employed to
determine the selectivity and indicate that besides higher yield, lower
diameter selectivity occurs above a critical diameter.
