Abstract We report inelastic neutron scattering investigations of hydrogen adsorbed on both purified boron substituted (≤1%) single walled carbon nanotube bundles and purified single walled carbon nanotube bundles. Samples of both types were generated by both arc and laser production methods. At H 2 coverages ≤3 H 2/B, a clear splitting is observed for the H 2 rotation transition peak at about 14.7 meV in all arc-produced samples. In contrast, the spectra from laser-produced materials exhibit one broad peak. Further increase in H 2 coverage results in adsorption at lower binding energy sites. No distinct signature of an enhanced boron–hydrogen interaction is observed. However, the overall line width of the rotation transition peak from a laser-produced sample is substantially smaller than that from arc-prepared samples. This difference might imply that some features of the H 2 rotation transition peak might not be due to the intrinsic features of single wall carbon nanotubes.