Effective mass ofHe3impurities inHe4films

We calculate the effective mass of ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ impurity atoms in a film of liquid ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ atoms adsorbed to a substrate. The calculated effective mas of the ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ impurity shows a strong dependence on the structure of the underlying ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ film. When both the coupling of the ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ impurity to the background and to other ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ impurities are taken into account, our values agree well with recent experiments by Wang and Gasparini [Phys. Rev. B 38, 11 245 (1988)]. It is suggested that the Fermi-liquid contribution to the effective mass is experimentally obsrevable.