Toward a Frequency Scanning Marginal Oscillator

Abstract

The advantages of a frequency scannable detector in ICR spectrometry have long been obvious. The ability to operate at constant magnetic field allows uniform trapping efficiency in trapped ion experiments and, in drift cell work, eliminates differential effects due to changing ion density, drift times and extents of reaction. Experiments where one ion is continually ejected are possible as well. That a great need exists for this type of detector is obvious from the tremendous interest in Bridge Circuit Detectors (BCD) which exists at present. A BCD suitable for ICR work was first presented by Wobschall [1] . McIver has recently developed a solid state version, [2,3] and other workers have followed [4] . Throughout this development, the possibilities of a frequency scannable Marginal Oscillator (MO) have been ignored. Recent work in our laboratory and others [1, 4, 5] indicate, however, that the sensitivity of the MO surpasses that of the BCD by a significant factor. While not universally applicable, the scanning MO appears to be the detector of choice in many experiments. We present here a summary of the requirements a scanning MO must fulfill, the basic approaches we have taken to satisfy them, and finally a short derivation of the relative sensitivities of Bridge Circuit and Marginal Oscillator detectors. A complete description of the scanning MO will be submitted for publication elsewhere.