Vibrational Energy Flow from Excited Adsorbates on Ionic Crystal Surfaces Measured by IR Polarization Interferometry and Laser Pulse Spectroscopy

Abstract

Abstract Vibrational energy flow in adsorbates on ionic crystal surfaces has been studied in situ by means of IR polarization interferometry, laser‐induced resonant desorption and fluorescence as well as time of flight measurements. Vibrational adsorbate spectra, isotherms and isosteric heats of adsorption were measured. The vibrationally induced desorption of CH 3 F and CD 3 F from NaCl(film) and NaCl(100) after resonant excitation of the v 3 ‐CF stretching vibration with a line‐tunable infrared laser is reported in detail. Translational temperatures T MB of the desorbing molecules were derived by fitting Maxwell‐Boltzmann distributions to the time‐of‐flight spectra. T MB of the molecules desorbing from NaCl(film) is much lower ( T MB = 30 K at substrate temperatures between 10 K and 78 K) than T MB of molecules desorbing from NaCl(100) ( T MB = 125 K), which is ascribed to the different adsorption energies on NaCl(film) and NaCl(100). No preferred desorption of CH 3 F or CD 3 F in a 45%:55% mixture at 0.75 of saturation coverage on NaCl(film) after resonant excitation was observed.