Note on Signal-to-Noise Ratios for Ion and Metastable Detection of Neutral Molecular Beams

S/N ratios for ion and metastable detection of neutral molecular beams which utilize time integrated measurements of an electron multiplier output are discussed. It is shown that the excitation probability is considerably less than the ionization probability for most molecules causing S/N improvements with metastable detection to be less than previously expected. An additional decrease results from the low electron yield of the metastable molecule compared to the ion at the electron multiplier surface.