Formation and characterization of methoxy isothiocyanate (CH3ON=C=S) and methyl cyanate N-sulfide (CH3OC N+-S-) as radical cations and neutrals in the gas phase

Dissociative ionization of heterocyclic precursors has provided a convenien t 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 isothiocyan ate, CH3ON=C=S.+ a, and the nitrile N-sulfide, CH3OC=N-S.+ b, connectivitie s. For the sake of comparison, a potential precursor of the isocyanate, CH3 SN=C=O.+ c, was also investigated. The gas phase stability of the correspon ding neutral molecules is indicated by the NR and NR/CA spectra. In additio n, consecutive collisional activation processes (MS/MS/MS spectra) were use d to characterize the structures of metastable ions which, in several cases , were found to be different from the corresponding ions generated in the i on source. Calculated ionization energies and enthalpies of reaction with N O. (at the G2(MP2,SVP) level) support the experimental characterization of ions a and b.