Determination of the appearance potentials of [C₃H₇]⁺ ions by a computerized electron distribution difference procedure

A simple computerized electron distribution difference method has been developed using a conventional mass spectrometer and an on‐line computer. Using the system, ionization potentials for various propyl halides were measured and found to agree well with photoionization data. The appearance potentials for [C₃H₇]⁺ agreed well with literature values, except for 1‐propyl bromide and 1‐ propyliodide which gave values approximately 0.7 eV lower than previous reports. The results are interpreted to indicate threshold formation of the sec‐propyl ion from all propul halides.