Transition metal sulfide studies: The pure rotational spectrum of the CuS radical (X²Π_i)

The pure rotational spectrum of CuS in its X²Π_i ground state has been recorded using direct absorption techniques in the range 140-540 GHz. This radical was produced by the reaction of copper vapour with CS₂. Both the v=0 and v=1 states of ⁶³CuS were observed, as well as the ⁶⁵CuS(v=0) isotopomer. 25, 13, and 8 rotational transitions were recorded for these three species, respectively. Both the Ω=1/2 and Ω=3/2 spin-orbit ladders were observed. Accurate rotational, spin-orbit, and lambda-doubling constants were subsequently determined for these molecules. These data suggest that 3d-sulfides have subtle bonding differences relative to the corresponding 3d-oxides.