The purpose of the present work is to provide a method for calculating the negative hydrogen ion yield due to fast and thermal ions and atoms versus the surface
work function. The value of the decay factor in Rasser’s equation is re-examined, to make possible the use of this equation to this aim. The analysis of the data from two experiments lead to two different values for the decay factor. The lower value, 2.13×10−5 eV s/m, allows to determine the yield of backscattered negative ions. The higher value, 6.4×10−5 eV s/m, leads to the total yield. The fractions of the negative ions produced by backscattering and desorption are determined.