Kinetic energy distributions from the shapes of metastable peaks

Abstract A general procedure is presented for determining the distribution of translational energies released in unimolecular ionic reactions occurring in the analyser of a mass spectrometer. It is shown that the method is applicable to reactions in which the average kinetic energy release covers a wide range (< 1 meV to ca. 3 eV). The treatment avoids making approximations either in the calculation of metastable peak shapes or in the subsequent determination of the translational energy distribution. Excellent agreement is achieved between experimental and calculated metastable peak shapes and the kinetic energy distributions represent the first accurate values obtained by a generally applicable technique. The relation between the average kinetic energy released and the width at half height of the corresponding metastable peak has been explored for peaks of various shapes. For gaussian-type peaks the kinetic energy release calculated from the half height is smaller by a factor of two to three than the average value, while for dish topped peaks it approximately equals the average value.