INFRARED RESONANCE-ENHANCED MULTIPHOTON IONIZATION OF FULLERENES

Gas-phase fullerenes are resonantly heated by a train of high power su bpicosecond pulses from a free electron laser (FEL) to internal energi es at which they efficiently undergo delayed ionization. When the lase r is tuned from 6-20 mu m while the amount of laser produced parent io ns is recorded, resonant absorption of 200-600 IR photons, resulting i n almost fragmentation-free ion spectra, is observed. Infrared resonan ce enhanced multiphoton ionization with a FEL is shown to enable extre mely sensitive IR spectroscopy with mass selective detection of gas-ph ase fullerenes. [S0031-9007(97)04923-5].