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Dissociative electron ionization (70 eV) of ethyl carbomylmethanedithioate generates m/z 77 ions of composition [H, C, S2]+. The collision-induced dissociation (CID) mass spectrum of these ions is consistent with the mercaptothiocarbonyl connectivity HSCS+ (a+). Calculations predict that some of the a+ ions may equilibrate with HC(S)S+ (b)+ ions prior to dissociation. Neutralization-reionization mass spectrum (NRMS) of these ions confirmed that neutral HSCS is stable in the rarefied gas phase. The relative, dissociation, and isomerization energies for the ions and neutrals studied at B3LYP/6-311G(d,p) and G2/G2(MP2) levels, are used to support and interpret the experimental results.

Electron ionization of rhodanine yields iminothiosulfine ions H – N  C – S – S + , 1b + , which readily communicate with the higher energy cyclic isomer H – N  CS 2 + , 1a + . CBS-QB3 and G aussian -2 model chemistries predict that one electron reduction reverses the stability order but that the (singlet) neutrals remain connected via a negligible energy barrier. Neutralization–reionization (NR) experiments demonstrate that singlet 1a and its heterocumulene isomer 1b are stable species in the gas-phase. However, the co-generated triplet species readily dissociate into 3 S 2 + + HNC . Confirmatory experimental evidence comes from charge reversal (CR) and NR experiments on the cyclic anion H – N  CS 2 − , 1a − .

The isomeric dicoordinated borinium ions CH3O–B–H+ and CH3–B–OH+ are generated upon electron ionization of trimethylborate and methyl boronic acid, respectively. The connectivity of the ions is confirmed by collision-induced dissociation experiments on magnetic deflection type tandem mass spectrometers. Neutralization–reionization experiments on these structurally characterized ions indicate that the neutral radicals CH3O–B–H· and CH3–B–OH· are viable species in the gas phase. Calculations at the G2 level of theory were performed to obtain thermochemical data on the title isomers and their main dissociation products. The calculations also provide a rationale for the moderate yield of the neutrals generated in the experiments: the vertical electron transfer processes for both systems are associated with particularly unfavourable Franck-Condon factors.

[Si,C,N,O]+ and [Si,C,N,S]+ cations formed upon electron ionization of trimethylsilyl isocyanate and isothiocyanate, respectively, are probed by tandem mass spectrometry. In the case of [Si,C,N,O]+, the experimental data suggest that the isocyanato group remains intact upon ionization such that silicon isocyanate SiNCO+ is formed. Neutralization-reionization mass spectrometry indicates that also neutral SiNCO is a viable molecule in the gas phase. Instead, partial isomerization to SiSCN+ is indicated for the sulfur analog. Because of this structural dichotomy, the nature of the [Si,C,N,S]+ species giving rise to the recovery signal in the neutralization-reionization experiments remains uncertain.

Results of tandem mass spectrometric experiments characterize both ionic and neutral dithioformic acid a, dimercaptocarbene b, and dithiirane c in the gas phase. Observed collisional activation spectra of the ion at m/z 78 from compounds ethyl carbamoylmethane dithioate 1, 5-amino-1,3,4-thiadiazole-2-thiol 2, and rhodanine 3 and 1,2-dithiacyclopentane 4 are most compatible with the connectivities a, b, and c, respectively. The NRMS experiments on these structurally characterized ions reveal that the neutral dithioformic acid a, dimercaptocarbene b, and dithiirane c are viable species in the gas phase. Relative energies of the CH2S2 isomers and their radical cations calculated at the B3LYP/6-31G** level support these experimental observations. Comparisons are made between the relative energies of the oxygen and sulfur analogues. The high relative energy of dioxirane g in relation to dithiirane c makes the former a difficult target for experimental observation.

NRMS experiments on the structurally characterized thiocarbonylisocyanate ion, [SCNCO]+, provide evidence for the existence of its neutral counterpart in the rarefied gas phase.

Results of the neutralization-reionization mass spectrometric (NRMS) experiments reveal that neutral (methythio)oxophosphane (CH3SP  O) and (methoxy)oxophosphane (CH3OP  O) are stable species in the gas phase.

In contrast to the oxygen analogue carbonylisocyanate [OCNCO], the thiocarbonylisothiocyanate [SCNCS] has been found to be a stable species on the neutralization-reionization mass spectrometry time scale.