193 nm Laser photoionization and photodissociation for isomer differentiation in Fourier-transform mass spectrometry.

Energetic (6.4 eV) multiphoton ionization (MPI) or photodissociation, effected interchangeably in a Fourier-transform mass spectrometer, can differentiate isomers that yield similar electron ionization spectra. Selectivity is shown for isomers of C7H8, C7H9N, C7H7F, C8H10, but not of C6H3Cl{3} and C14H10. The contrasting MPI fragmentations and ionization efficiencies, as well as high sensitivities, are of substantial analytical utility. The high ionization efficiency makes possible high resolution MPI spectra, such as 470,000 (FWHH) for the molecular ion of anthracene, from a single laser pulse.