Inefficient Vibrational Cooling of C60 in a Supersonic Expansion

High-resolution gas-phase infrared spectroscopy of buckminsterfullerene (C 60) was attempted near 8.5 μm using cavity ring-down spectroscopy. Solid C 60 was heated in a high-temperature ( ~950 K) oven and cooled using an argon supersonic expansion generated from a 12.7 mm × 150 μm slit. The expected ratio is ~140 for vibrationally cold C 60, but no absorption signal has been observed, presumably due to a lack of vibrational cooling of C 60 in the expansion. Measurements of D 2O at 875 K are presented as a test of instrument alignment at high temperature and show that efficient rotational cooling of D 2O occurs in the hot oven (  = 20 K in the expansion), though vibrational cooling does not occur. The attempted C 60 spectroscopy is compared to previous work which showed efficient vibrational cooling of polycyclic aromatic hydrocarbons (PAHs). Possible alternative experiments for observing a cold, gas-phase spectrum of C 60 are also considered.