An account is given of the first infrared vibrational photon echo experiments conducted in liquids and a glasses. The experiments were performed on the CO stretching mode of the solute tungsten hexacarbonyl (W(CO)6) at approximately 5.05 micrometers (approximately 1980 cm-1) in the solvents 2-methytetrahydrofuran, and 2-methylpentane (2-MP). In 2-MP, it was possible to observe the photon echo decay at room temperature and follow the temperature dependence from room temperature to 10 K. The photon echo experiments were conducted using the Stanford superconducting-linear-accelerator-pumped Free Electron Laser as the source of tunable ps infrared pulses.
Intense tunable vibrational infrared pulses from a free-electron laser and from a laser-pumped optical parametric amplifier can be used to study molecular energy transfer in condensed phase systems. Specific examples discussed here are energy transfer at the active site of a protein, myoglobin, studied by infrared-infrared pump-probe techniques, and energy transfer in a high explosive, nitromethane, probed by infrared-pump, anti-Stokes Raman probe techniques.