Structural studies of alkali methylidyne radicals: High resolution spectroscopy of NaCH and KCH (X̃³Σ^-)

High resolution spectroscopic measurements have been carried out for alkali methylidyne radicals. The pure rotational spectra of NaCH and KCH, along with their deuterium isotopomers, have been recorded in the frequency range 328-529 GHz using millimeter/submillimeter direct absorption techniques. These molecules were created in a dc discharge by the reaction of metal vapor and CH₄ or CD₄. These data indicate that KCH and NaCH are linear molecules with ³Σ^- ground electronic states arising from a π² configuration. Spectroscopic constants for KCH and NaCH have been determined from the data, including rotational, spin-spin, and spin-rotation parameters, as well as bond lengths. In comparison with other alkali and transition metal-bearing molecules, these results suggest some degree of covalent bonding in the alkali methylidynes, with carbon atom undergoing sp hybridization.