Millimeter-wave spectra of CaSH and CaSD

The pure rotational spectra of CaSH and CaSD were observed using millimeter-wave absorption spectroscopy. The gas phase free radicals were produced in a high-temperature cell by the reaction of Ca vapor with H2S or D2S in the presence of an electrical discharge. The spectra were analyzed using an S-reduced Hamiltonian. The molecular constants including the rotational constants, centrifugal distortion constants, and spin-rotation constants were extracted from the spectra. The off-diagonal spin-rotation term, ‖εab+εba‖/2, is 3.38(12) MHz and 4.59(4) MHz for CaSH and CaSD, respectively. The moment of inertia data of CaSH and CaSD yielded the r0 structure. The three structural parameters are Ca–S=2.564(2) Å, S–H=1.357(17) Å, and ∠Ca–S–H=91.0(18)°.