Measurement of the mean transverse kinetic energy of recoil ions produced in energetic electron–atom collisions

A realistic approach for determining the mean transverse kinetic energy (MTKE) of recoil ions produced in energetic electron–atom collisions from the knowledge of full width at half maximum of the ion peaks has been described and discussed. The method is independent of any critical assumption and requires only the input values of 'optimized parameters' of the time-of-flight mass spectrometer employed for detecting the recoil ions. The method has been used to calculate the MTKE of argon recoil ions produced in 24 keV e⁻ – Ar collisions. The results obtained are compared with those determined from a relation given by Olson (Olson R E 1979 J. Phys. B: At. Mol. Phys. 12 1843); the agreement between the two results is found to be reasonably good within the experimental uncertainty of the measurements. Further, from dependences of MTKE on charge state fractions F_r of recoil ions and on their charge states q, it is found that F_r varies with q as 1/q⁴ for multiple ionization of atoms by impact of energetic electrons, unlike as 1/q² for multiple ionization of atoms by impact of energetic highly charged heavy ions.