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The CH4 + electroionisation efficiency curve and the CH3 +, CH2 +, CH+ and C+ appearance potential curves are presented. The data were obtained by an apparatus of very high sensitivity with an improved electron monochromator. The CH4 + ionisation potential is measured to be 12.63+or-0.02 eV. The results show that some previously reported appearance potential values should be corrected, in some cases by several electron volts. This is attributed to superior apparatus sensitivity. Ion-pair formation is clearly observed for the CH3 + and CH+ fragments. The CH+ and C+ appearance potentials have been detected down to adiabatic threshold. The stable fragment CH2 2+, is also observed.

A cylindrical electrostatic electron selector is described which provides a 10−7 ampere beam of electrons whose energy may be varied from 0 to 50 ev and whose energy spread is less than 100 mv. Space-charge problems involved in the construction of the device were overcome by the use of grids for focusing electrodes with exterior electron traps, and a non-reflecting surface for electrons made from a network of tiny tubes. The selector is provided with an energy analyzer. When used to determine the appearance potential curve of argon, the selector resolved the 2P3/2 and 2P1/2 states separated by 0.18 ev, and indicated the formation of [Formula: see text] at an energy of 0.8 ev below the threshold for A+.

The extremely simple mathematical technique called ''straightening through smoothing,'' which is a numerical frequency filter, is generalized in order to provide a transmission function having any shape. This frequency filter requires such a small memory that it can be performed using a minicomputer or even a programmable hand held calculator and the number of channels used is not limited to a power of 2, as in the case of the fast Fourier transform. For some filtering functions the number of operations required is smaller than with the fast Fourier transform.

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