Raman Spectroscopic Investigation of H2, HD, and D2 Physisorption on Ropes of Single-Walled, Carbon Nanotubes

We have observed the S- and Q-branch Raman spectra of H2, HD, and D2 adsorbed at 85K and pressures up to 8 atm on single-walled, carbon nanotubes (SWNT). Comparative data for H2 on graphite and C60 were also collected. For each adsorbate, we observed a small shift in the Q-branch frequencies relative to the gas-phase values. To aid in interpreting this result, we constructed an H2-surface potential, including van der Waals and electrostatic terms. Computed shifts based on this potential are in good agreement with our data.