Accurate ab initio calculations are performed in order to characterize the most stable isomers of empirical formula C3S+ and the role of C3S+ during the ion-molecule reactions between the C-3(+) triatomic molecular ions and S atoms. The linear form l-C-C-C-S+(X(2)Sigma(+)) is found to be the most stable isomer followed by a three-membered carbon ring with an external S {c-C3S+(X(2)A(1))}. The ion-molecule reactions are investigated by doing suitable 1-D cuts of the 6-D potential energy functions (PEFs) of the lowest electronic states of C3S+. After its formation, the C3S+ intermediate may dissociate leading, in addition to the charge transfer products, to C, C 1, C-2, C-2(+), CS, CS+, C2S and C2S+ species. Generally, the dynamics of these reactions are found to involve several electronic states of C3S+ and their mutual couplings, including Renner-Teller couplings, spin-orbit interactions and vibronic interactions. These couplings can take place before and/or after intramolecular isomerisation processes.