The pure rotational spectrum of KH (X-1 Sigma(+)): Quadrupole coupling in alkali hydrides

The pure rotational spectrum of KH (X(1)Sigma (+)) has been recorded using millimeter/submillimeter direct absorption techniques. The species was crea ted by the reaction of potassium vapor and H-2 in a d.c. discharge. The J = 0 -->1 and 1 -->2 transitions were measured near 202 and 404 GHz, and elect ric quadrupole splittings were resolved in the J=0 -->1 line and partly res olved in the other transition. For comparison, the quadrupole structure in the J=0 -->1 transition of NaH (X(1)Sigma (+)) was also recorded. Very accu rate rotational and quadrupole hyperfine constants were determined for KH, and eqQ was established for NaH as well. Diatomic hydride species are the b uilding blocks for interstellar chemistry in both dense and diffuse gas. Kn owledge of the rest frequencies of KH will enable its detection in such obj ects.