Results of measurements of the total yield of H−ions due to surface conversion of H+and H2+ions at low work function surfaces are presented. A low energy (3–50 eV) ion beam strikes the target at normal incidence. All secondary charged particles are collected. Calculations of the theoretical negative ion yield as a function of incident perpendicular energy have been modified to include energy and particle losses due to scattering. The scattering is modeled using TRIM calculations of particle and energy reflection coefficients. A cosine distribution in scattering angle has been assumed. The surface investigated was polycrystalline molybdenum, cesiated by vapor deposition. The work functions were determined by measurements of photoemission threshold of these surfaces. H−and electron yields were determined by taking the ratio of the secondary charged particle currents to the proton current to the target. Secondary electrons were suppressed by a magnetic field. H−and electron yields of order 20% per incident nucleon were obtained.