  The coupling of an electron monochromator (EM) to a mass spectrometer (MS)
has created a new analytical technique, EM-MS, for the investigation of
electrophilic compounds. This method provides a powerful tool for molecular
identification of compounds contained in complex matrices, such as
environmental samples. EM-MS expands the application and selectivity of
traditional MS through the inclusion of a new dimension in the space of
molecular characteristics--the electron resonance energy spectrum. However,
before this tool can realize its full potential, it will be necessary to create
a library of resonance energy scans from standards of the molecules for which
EM-MS offers a practical means of detection. Here, an approach supplementing
direct measurement with chemical inference and quantum scattering theory is
presented to demonstrate the feasibility of directly calculating resonance
energy spectra. This approach makes use of the symmetry of the
transition-matrix element of the captured electron to discriminate between the
spectra of isomers. As a way of validating this approach, the resonance values
for twenty-five nitrated aromatic compounds were measured along with their
relative abundance. Subsequently, the spectra for the isomers of nitrotoluene
were shown to be consistent with the symmetry-based model. The initial success
of this treatment suggests that it might be possible to predict negative ion
resonances and thus create a library of EM-MS standards.
