On the determination of the velocity distribution of photodesorbed atoms from their excitation spectra

A novel method to determine velocity and angular distributions of photodeso rbed particles is developed. It is based on the spectrally resolved detecti on of the desorbing particles. Its validity is exploited by analyzing Doppl er-broadened, resonance-enhanced two-photon ionization spectra of alkali at oms, photodesorbed from large, surface-bound Na clusters. Comparison with a rigorous theoretical approach shows that one can easily distinguish betwee n different kinds of velocity distributions of the desorbing particles, viz . Maxwellian versus non-Maxwellian or different powers n of the cos(n) thet a angular distributions. (C) 1999 Elsevier Science B.V. All rights reserved .