The use of femtosecond laser pulses to induce the dynamics of molecules on metal surfaces has a wide range of applications, including materials processing and time-resolved spectroscopy. Intense femtosecond laser pulses can also be applied in surface photochemistry and photocatalysis, where increased reaction cross-sections, different reaction pathways, nonthermal product energy distributions, and even different products compared to those observed under thermal conditions, are observed. Light pulses in the ultraviolet, visible, and near-infrared ranges are absorbed by the metal, leading to electronic excitations that are then transferred to the lattice atoms through electron-phonon coupling. The interplay of direct electronic and indirect phononic energy transfer to the adsorbates triggers a range of photo-induced phenomena. One of the paradigmatic experimentally well-studied systems is femtosecond laser-induced recombinative desorption of H 2 , D 2 , and HD from Ru(0001) surfaces covered with atomic hydrogen or deuterium, see the detailed review in ref 3. Some of the conclusions of experimental studies are that the desorption process exhibits a significant isotope effect, with a higher probability of desorption for hydrogen (H 2 ) than deuterium (D 2 ). The desorption yield increases according to a power law with increasing fluence. The desorbing molecules have a velocity distribution that follows a Maxwell-Boltzmann distribution, but with a temperature that is much higher than expected from a purely thermal desorption mechanism.