Characterization of C2S4 center dot+ isomers by mass spectrometry and ab initio molecular orbital calculations

Isomeric C2S4.+ radical cations, a dimer (CS2)CS2.- and a covalently bounde d C2S4.+ species, are generated by chemical ionization (self-chemical ioniz ation conditions) of carbon disulfide or by dissociative electron ionizatio n of 1,3,4,6-tetrathiapentalene-2,5-dione and 1,2-dithiolo[4,3-c][1,2]dithi ole-3,6-dione, respectively. These ions axe structurally characterized maki ng use of mass spectrometric methodologies such as collisional activation, neutralization-reionization and ion-molecule reactions performed in a hybri d tandem mass spectrometer of sector-quadrupole-sector configuration. These experimental results are supported by ab initio calculations of the relati ve energies of 19 possible isomers indicating that the most stable C2S4.+ s tructure corresponds to a CS2 dimer with a C-2 symmetry, 52 kJ mol(-1) more stable than the lowest-energy covalently bound structure consisting of a f our-membered ring thioketene species. (C) 2001 Elsevier Science B.V.