Inefficient Vibrational Cooling of C60 in a Supersonic Expansion

High-resolution gas-phase infrared spectroscopy of buckminsterfullerene (C 60 ) was attempted near 8.5 μmusing cavity ring-down spectroscopy. Solid C 60 was heated in a high-temperature (∼950K) oven and cooled using an argon supersonic expansion generated from a 12.7mm × 150 μm slit.The expected S/N 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 2 O at 875K are presented as a test of instrument alignment at high temperature and show that efficient rotational cooling of D 2 O occurs in the hot oven (Trot = 20K 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.