Molecular velocities in laser-induced vibrational predesorption

Desorption by resonant excitation of the ν7 normal mode of the adsorbate with infrared laser radiation was observed in the system (CH2 = CH2) NaCl. The fluence dependence of time-of-flight distributions was investigated, providing the intensity dependence of the molecular velocities in laser-induced vibrational predesorption for the first time to our knowledge. Maxwell–Boltzmann distribution functions could be fitted precisely to the experimental distributions. The temperatures associated with the time-of-flight distributions in the limit of small fluence turned out to be equal to the adsorbent temperatures set between 35 and 100 K. For highly dispersed adsorbent films, a strong linear dependence of the translational energies on laser intensity was found. For single-crystal and annealed-film surfaces, intensity independence or weak intensity dependence of the molecular velocities was observed.