We report inelastic neutron scattering results on hydrogen adsorbed onto sa
mples containing single-wall carbon nanotubes. These materials have attract
ed considerable interest recently due to reports of high density hydrogen s
torage at room temperature. Inelastic neutron scattering clearly shows the
ortho-para conversion of physisorbed hydrogen in a nanotube containing soot
loaded with hydrogen. From the rotational J = 0 --> 1 transition, no indic
ation of a significant barrier to quantum rotation is seen. (C) 2000 Elsevi
er Science B.V. All rights reserved.