The effect of backflow on atom emission from the free surface of superfluid He-4 by rotons

We extend the theory of Sobnack and Inkson (Phys. Rev, Lett. 82 (1999) 3657 ) by including roton backflow semi-phenomenologically in the form of a back flow potential to examine the effect of backflow on the quantum evaporation of atoms from superfluid helium by rotons. We solve the resulting equation s numerically and calculate the probabilities P-ra of atom (a) emission by both R+ and the negative group velocity R- rotons (r). We compare the resul ts with the corresponding efficiencies when backflow is neglected and we co mment on the improved agreement with experiments. (C) 2000 Elsevier Science B.V. All rights reserved.