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

A novel method to determine velocity and angular distributions of photodesorbed particles is developed. It is based on the spectrally resolved detection of the desorbing particles. Its validity is exploited by analyzing Doppler-broadened, resonance-enhanced two-photon ionization spectra of alkali atoms, photodesorbed from large, surface-bound Na clusters. Comparison with a rigorous theoretical approach shows that one can easily distinguish between different kinds of velocity distributions of the desorbing particles, viz. Maxwellian versus non-Maxwellian or different powers n of the cosn θ angular distributions.