Knowledge Bank

We report here the first study of the rotational spectrum of an open-shell polyatomic ion. $H2O+$ is produced in an intracavity A.C. discharge using 1 torr of helium and a trace of water vapor. Fifty-five hyperfine-Zeeman lines have been measured from three different rotational transitions, revealing both singlet and triplet hyperfine structures from the protons. An analysis is underway employing a Watson S-reduced Hamiltonian with electron spin, hyperfine, and Zeeman interaction terms. The LMR data is supplemented by optical conbination differences in a weighted least-squares fit. Results of the fit provide information on the electron distribution in the ion and ultimately will yield a precise molecular structure. $H2O+$ is a molecule of both astrophysical and atmospheric interest, and has been observed in the tails of comets. This high resolution study by LMR will yield colecular constants necessary for the prediction of accurate rest frequencies to be used in searches for $H2O+$ in these environments. This work was supported by the Director, Office of Basic Research, U.S. Department of Energy.