Infrared resonance enhanced multiphoton ionization of fullerenes

Gas-phase fullerenes are resonantly heated by a train of high power subpicosecond pulses from a free electron laser (FEL) to internal energies at which they efficiently undergo delayed ionization. When the laser is tuned from 6-20 mu m while the amount of laser produced parent ions is recorded, resonant absorption of 200-600 IR photons, resulting in almost fragmentation-free ion spectra, is observed. Infrared resonance enhanced multiphoton ionization with a FEL is shown to enable extremely sensitive IR spectroscopy with mass selective detection of gas-phase fullerenes. [S0031-9007(97)04923-5].