The pure rotational spectrum of CaNH₂ and CaND₂ (X̃²A₁): Additional proof of planarity

The pure rotational spectrum of CaNH₂ in its X̃²A₁ ground electronic state has been recorded using millimeter/submillimeter direct absorption methods in the frequency range 320-537 GHz as well as that of CaND₂. The species were created by Broida-oven techniques. Eleven rotational transitions were observed arising from the v=0 and v₆=1 states of CaNH₂, and eight transitions were recorded for the v₃=1 and v₄=1 levels. For CaND₂, eight transitions (v=0) were also measured. For the majority of these transitions, K_a doublets corresponding to K_a=0-5 were observed and fine structure splittings were resolved in every component. These spectra were analyzed using an S-reduced Hamiltonian; rotational, centrifugal distortion, and spin-rotation parameters were determined for CaNH₂, CaND₂, and the three observed vibrationally excited states. An r₀ structure has also been calculated. The data are consistent with calcium amide being a planar molecule with C_2v symmetry and having predominately ionic bonding, as indicated by previous optical studies.