Collision spectroscopy in isomer characterization: The case of (E)- and (Z)-p-nitrophenyldiazotert-butyl sulphides

Abstract

The structural characterization of the E and Z isomers of p-nitrophenyl-diazo tert-butyl sulphide has been achieved by means of different ionization methods (electron impact, fast atom bombardment, positive-ion chemical ionization) and collision experiments performed under different kinetic energy regimes (high- and low-energy collisions, angle-resolved mass spectrometry and energy-resolved mass spectrometry). The two compounds give rise to identical fragmentation patterns. Collision experiments, both at low energy and in the keV range at a scattering angle of 0°, in M+· species obtained by electron impact on the two isomers, do not show any significant differences; the same experiments performed with 8 keV ions at a scattering angle of 2° indicate a clear difference in the absolute abundances of the two main daughter ions. High-energy collisions of MH+ ions obtained by fast atom bombardment lead to different spectra at both 0° and 2° scattering angles, proving that the energy deposition in the preselected species is an important parameter. Low-energy collisions with argon of MH+ ions generated by positive-ion chemical ionization (NH4+) give rise to almost identical energy-resolved mass spectra, whereas the same experiments using helium as target gas lead to a clear distinction between the two isomers.