The design and operation of an automated, high-efficiency photoionization mass spectrometer

A computer-controlled photoionization mass spectrometer is described, as are operating procedures designed to achieve maximum possible efficiency during data acquisition, and very high efficiency overall. The software necessary to implement these procedures, as well as a set of guidelines which have been developed for facilitating user-computer interaction, are also described. An extensive safety interlock system, which monitors and controls the complex vacuum system and other utilities, is described in detail, as are the computer-interface electronics. The latter includes a unique pulse amplifier circuit designed for fast photon or ion-counting applications. The new instrument has been used to study the mixed chlorofluoromethanes CFCl3, CF2Cl2, and CF3Cl. There is some evidence that the observed parent ion appearance potentials may be significantly above the adiabatic ionization potentials for all three molecules, and further work is recommended to resolve several apparent paradoxes in presently available data for both parent and fragment ions.