High-resolution infrared absorption spectroscopy of C-60 molecules and clusters in parahydrogen solids

We report the isolation of C-60 molecules in cryogenic parahydrogen (pH(2)) solids by the rapid vapor deposition method. New theoretical simulations o f rovibrational spectra for low-temperature isolated C-12(60) molecules, in cluding boson-exchange symmetry restrictions on the rotational levels, pred ict a characteristic "null gap" and unequal rotational line spacings for lo w-J values. High-resolution IR absorption spectra of the C-60/pH(2) samples failed to show rotationally resolved features, and in fact suggest that th e majority of the C-60 molecules are not rotating. However, spectra of the F-1u(1) vibrational mode near 530 cm(-1) show line widths of approximate to 0.2 cm(-1) fwhm, the sharpest IR absorption bands for C-60 reported to dat e. Visible absorption spectra also show sharp features in the approximate t o 600 nm region, supporting our contention of well-isolated C-60 molecules. The C-60 molecules appear to stabilize the pH(2) solid, inhibiting the fee to hcp conversion which usually occurs upon annealing of rapid vapor depos ited pH(2) solids to T approximate to 5 K. We also report surprisingly stro ng C-60-induced IR activity in the pH(2) solid, and propose this phenomenon as a diagnostic for H-2 molecules adsorbed by carbon nanotubes, C-60/pH(2) samples grown in an enclosed cell by laser ablation of solid C-60 appear t o contain predominantly (C-60)(n) clusters; these clusters are too small to exhibit "bulk" vibrational or electronic properties, as determined by IR a nd UV/visible absorption spectroscopies. Future experiments to disentangle the contributions of C-13 isotopic substitution, pH(2) matrix effects, and the putative hindered rotation of C-60 molecules to the observed C-60/pH(2) IR line shapes are presently under consideration.