Abstract

The infrared free-electron laser (IRFEL) is a useful light source that can be employed as a probe of vibrational dynamics on surfaces. We explore in detail two possible applications of the IRFEL. One type of experiment utilizes the IRFEL to measure vibrational relaxation on surfaces directly, using infrared saturation and ground-state recovery techniques. The second application uses the IRFEL to desorb adsorbates from surfaces by resonantly exciting their vibrational modes. This application is illustrated by recent investigations of the resonant desorption of butane from Al₂O₃(11 $\overline{2}$0), using the Mark III IRFEL. These studies revealed a greater desorption yield for the asymmetric C—H stretches in comparison with the symmetric C—H stretches. This greater desorption efficiency for the asymmetric C—H stretches was attributed to the orientation of the butane molecules in an ordered adlayer on Al₂O₃(11 $\overline{2}$0). Future applications of the IRFEL as a probe of vibrational dynamics on surfaces are also discussed.

© 1989 Optical Society of America

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