THE WAVE-VECTOR DEPENDENCE OF QUANTUM EVAPORATION FROM SUPERFLUID HE-4

Absolute measurements of the probability of quantum evaporation of ato ms by rotons from the surface of superfluid He-4 are still problematic . However, it is possible to obtain information about the wave-vector dependence of the evaporation process by using a refined simulation(14 ) to interpret the experiments of Brown and Wyatt(12). Two theories (G uilleumas et al.(9) and Sobnack et al. (10)) are compared with these e xperiments by incorporating their predictions for the quantum evaporat ion probability into a numerical simulation. Both theories over-estima te the probability of phonon-atom evaporation. For roton (R+-atom) eva poration, compared with a simulation that assumes all kinetically allo wed events are equally probable, the theory of Guilleumas et al. does not significantly improve the agreement with experiment, and the theor y of Sobnack et al. increases the discrepancy. PACS numbers: 67.40.Db, 68.45.Da, 67.40.-w.