Metastable ion studies X - A Monte Carlo method for the computation of metastable peak shapes

Abstract

A Monte Carlo method is described for computing metastable peak shapes using either an assumed or an experimentally probability distribution, n( T) for the released kinetic energy, T. The present study also considers the effect of Z-axial discrimination on metastable peak shape. It is shown that for the probability distribution obtained from Gaussian metastable peaks, which is of the form: n( T) = T 1 2 e −σ T , the effect of Z-axial discrimination (AEI-GEC MS902S mass spectrometer) on the peak shape is only slight for distributions where T (average) ⩽ 1 eV. Using n( T) curves obtained from experimental observations, this Monte Carlo method accurately regenerates the original metastable peak, demonstrating the validity of our analytical method for deriving energy release distributions. It is concluded that, within the above range of T, physicochemical rather than instrumental effects are responsible for the marked deviations from pure Gaussian shape that are observed in many metastable peaks. Preliminary applications of the method to composite and flat-topped (or dished) metastable peaks are also described.