High-Resolution Infrared Absorption Spectroscopy of C60 Molecules and Clusters in Parahydrogen Solids

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Vol. 104; no. 16; pp. 3733 - 3742
• Main Authors: Sogoshi, Norihito, Kato, Yoshiyasu, Wakabayashi, Tomonari, Momose, Takamasa, Tam, Simon, DeRose, Michelle E, Fajardo, Mario E
• Format: Journal Article
• Language: English
• Published: American Chemical Society 27.04.2000
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/jp9938718

We report the isolation of C60 molecules in cryogenic parahydrogen (pH2) solids by the rapid vapor deposition method. New theoretical simulations of rovibrational spectra for low-temperature isolated 12C60 molecules, including boson-exchange symmetry restrictions on the rotational levels, predict a characteristic “null gap” and unequal rotational line spacings for low-J values. High-resolution IR absorption spectra of the C60/pH2 samples failed to show rotationally resolved features, and in fact suggest that the majority of the C60 molecules are not rotating. However, spectra of the F1u(1) vibrational mode near 530 cm-1 show line widths of ≈0.2 cm-1 fwhm, the sharpest IR absorption bands for C60 reported to date. Visible absorption spectra also show sharp features in the ≈600 nm region, supporting our contention of well-isolated C60 molecules. The C60 molecules appear to stabilize the pH2 solid, inhibiting the fcc to hcp conversion which usually occurs upon annealing of rapid vapor deposited pH2 solids to T ≈ 5 K. We also report surprisingly strong C60-induced IR activity in the pH2 solid, and propose this phenomenon as a diagnostic for H2 molecules adsorbed by carbon nanotubes. C60/pH2 samples grown in an enclosed cell by laser ablation of solid C60 appear to contain predominantly (C60) n clusters; these clusters are too small to exhibit “bulk” vibrational or electronic properties, as determined by IR and UV/visible absorption spectroscopies. Future experiments to disentangle the contributions of 13C isotopic substitution, pH2 matrix effects, and the putative hindered rotation of C60 molecules to the observed C60/pH2 IR line shapes are presently under consideration.