C2H2S radical cations: Application of tandem mass spectrometry methodologies ☆

Abstract Attempts have been made to characterize ionic and neutral C 2 H 2 S +/o isomers, viz. , thioketene ( 1 + ), ethynylthiol ( 2 + ), and thiirene ( 3 + ) using various tandem mass spectrometric methodologies. Dissociative electron ionization of thiophene, 1-propane thiol and thiirane were used to produce the C 2 H 2 S + ( m / z 58) ions. The collisional activation (CA) mass spectrum of m / z 58 ions from thiophene is highly compatible with thioketene ions which has been supported by the CA mass spectrum of metastably generated m / z 58 ions and by comparison with the previously reported CA mass spectrum of thioketene ions. Theoretical calculations at the B3LYP/6-311G(d,p), and G2/G2(MP2) levels predict that low energy thioketene ions equilibrate with other isomeric ions viz. , ethynylthiol and thiirene prior to dissociation by loss of H ( m / z 57) and CH ( m / z 45). The CA spectra of C 2 H 2 S + ions from 1-propane thiol and thiirane are nearly identical indicating a facile isomerization of the initial structures at energies lower than the dissociative threshold. The low energy CID spectra of the m / z 58 ions from three precursors are found to be similar. However, significant differences are noticed in the relative abundances of product ions in the NR spectra of m / z 58 ions from the three precursors. While the NR mass spectra of m / z 58 ions from thiophene and thiirane confirms the stability of thioketene neutrals, the NR spectra of m / z 58 ions from 1-propane thiol suggests formation of a mixture of ethynylthiol and thioketene ions. Calculations predict a different thermo-chemistry for 1 + – 3 + , but, due to a mixture of reacting isomeric ions whatever the precursor molecule is, similar results were obtained for the associative ion/molecule reactions between the C 2 H 2 S + ions with methylisocyanide.