Distortions of Time-of-Flight Signals

Use of the time-of-flight (TOF) technique in molecular beam applications is reviewed. If the peak signal height and the hydrodynamic flow time are used as the normalization quantities, then a convenient dimensionless TOF signal is obtained in a double-convolutional integral form which involves three dimensionless functions: the molecular beam speed distribution function, the chopper gate function, and the dynamic function of the detector and its electronics. The latter two functions are characterized, respectively, by the dimensionless characteristic times T̃ and τ̃e. Numerical examples demonstrate distortions of TOF signals caused by these characteristic times and errors made in analyzing TOF signals when not taking into account the effects of T̃ and τ̃e. The orders of magnitudes of T̃ and τ̃e are not negligible; therefore, their effects should be treated in TOF signal data reductions.