Formation and characterization of methoxy isothiocyanate (CH3ONCS) and methyl cyanate N-sulfide (CH3OCN+–S–) as radical cations and neutrals in the gas phase

Abstract

Dissociative ionization of heterocyclic precursors has provided a convenient source of isomeric [CH₃O,C,N,S]^˙+ radical cations. Metastable ion (MI), collisional activation (CA), neutralization–reionization (NR) spectra, and ion–molecule reactions, performed in a hybrid tandem mass spectrometer of sectors–quadrupole–sectors configuration, have demonstrated the isothiocyanate, CH₃ONCS^˙+ a, and the nitrile N-sulfide, CH₃OCN–S^˙+ b, connectivities. For the sake of comparison, a potential precursor of the isocyanate, CH₃SNCO^˙+ c, was also investigated. The gas phase stability of the corresponding neutral molecules is indicated by the NR and NR/CA spectra. In addition, consecutive collisional activation processes (MS/MS/MS spectra) were used to characterize the structures of metastable ions which, in several cases, were found to be different from the corresponding ions generated in the ion source. Calculated ionization energies and enthalpies of reaction with NO˙ (at the G2(MP2,SVP) level) support the experimental characterization of ions a and b.