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Abstract-Field-ionization (FI) mass spectrometry is an established method for obtaining abundant molecular ions' of a variety of compounds, and recently has been used in conjunction with exact mass measurements for determination of elemental compositions of molecules.2J Very little, however, has been reported on the value of normal fragment ions and metastable ions appearing in the FI spectrum as a source of structural information.

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Abstract-Preliminary results indicate the value of ion kinetic energy (IKE) spectra in adding a new dimension to structural information obtained by mass spectrometry. These spectra are especially useful in the distinction of some isomer pairs. Energy spectra provide a summary of gaseous ion chemistry occurring as metastable transitions in the first-field free-drift region of the double-focusing (Mattauch-Herzog geometry) mass spectrometer and are produced by scanning the electrostatic sector voltage while recording the ion? transmitted by the sector with the beam monitor electrometer. I N T R O D U C T I O NTHE TECHNiQuE of defocusing the double-focusing mass spectrometer for the sensitive observation of metastable ions and assignment of metastable transitions is well established1,2 and has been discussed specifically for mass spectrometers of the Mattauch-Herzog A variation of this technique produces a unique spectrum for the metastable transitions observed for a particular compound. Production of these ion kinetic energy (IKE) spectra was first demonstrated by Beynon5s7 using double-focusing instruments of the Nier-Johnson geometry. In this report, results obtained using an instrument of the Mattauch-Herzog geometry are sunimarized.In defocused metastable experiments described previously, the daughter ions from the precursor decompositions are observed by variation of the magnetic field to focus the mass in2 or m t as allowed by the appropriate accelerating or electrostatic sector voltage. If, however, only kinetic energy of the daughter ions is considered, a spectrum of the metastable transitions of a particular sample may be recorded without consideration of the mass. R E S U L T S A N D DISCUSSIONIf the electrostatic sector of the mass spectrometer is scanned, the individual ion beams of varying kinetic energy resulting from the daughter ions of metastable decompositions may be scanned across the electrodes of the beam monitor. The resultant IKE spectrum plots the kinetic energy 1's. abundance of daughter ions allowing a summary of all metastable transitions in a single experiment. A typical IKE spectrum for decane is shown in Fig. I .The main or normally focused beam of the mass Spectrometer with an ion accelerating voltage (kinetic energy) of 8 kV is observed at an electrostatic sector voltage of 400 Vr producing an intense ion signal at the left hand side of the spectrum.