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Chlorothiophenols (CTPs) are known to be key and direct precursors of polychlorinated thianthrene/dibenzothiophenes (PCTA/DTs). Self/cross-coupling of the chlorothiophenoxy radicals (CTPRs), sulfydryl-substituted phenyl radicals and thiophenoxyl diradicals evolving from CTPs are initial and important steps for PCTA/DT formation. In this study, quantum chemical calculations were carried out to investigate the homogenous gas-phase formation of PCTA/DTs from self/cross-coupling of 2,4-dichlorothiophenoxy radical (R1), 2-sulfydryl-3,5-dichlorophenyl radical (R2) and 3,5-dichlorothiophenoxyl diradical (DR) at the MPWB1K/6-311+G(3df,2p)//MPWB1K/6-31+G(d,p) level. The rate constants of crucial elementary steps were deduced over 600&#8722;1200 K, using canonical variational transition state theory with a small curvature tunneling contribution. For the formation of PCTAs, the S&#8226;/&#963;-C&#8226; condensation with both thiophenolic sulfur in one radical and <i>ortho</i> carbon in the other radical bonded to single electron is the most efficient sulfur-carbon coupling mode, and the ranking of the PCTA formation potential is DR + DR &gt; R2 + DR &gt; R1 + DR &gt; R1 + R2 &gt; R1 + R1. For the formation of PCDTs, the &#963;-C&#8226;/&#963;-C&#8226; coupling with both <i>ortho</i> carbon in the two radicals bonded to single electron is the energetically favored carbon-carbon coupling mode, and the ranking of the PCDT formation potential is: R2 + DR &gt; R2 + R2 &gt; R1 + DR &gt; R1 + R2 &gt; R1 + R1. The PCTA/DTs could be produced from R1, R2 and DR much more readily than PCDD/DFs from corresponding oxygen substituted radicals.