Threshold Photoelectron Detector for Use in the Vacuum Ultraviolet

Abstract

The device described responds selectively to those photoelectrons that are formed practically at rest in a gaseous target. The energy discrimination is achieved by accelerating the charged particles to reject those formed with appreciable transverse velocity. When this is used in connection with a light source of continuously variable wavelength over the range 10–20 eV, the resulting threshold photoelectron spectra allow the direct spectroscopic determination of ionization energies within a few millielectron volts. The potential of the method for detection of direct ionization and suppression of autoionization is illustrated by measurements of argon, krypton, and xenon. Simultaneously, ions can also be detected by use of a mass spectrometer. Thus the threshold photoelectron spectrum can be correlated with the photoion spectrum; and it is suggested that the method is applicable to coincidence measurements between electrons and ions.