THE MILLIMETER-WAVE SPECTRUM OF THE CAOH RADICAL (X2-SIGMA+)

The pure rotational spectrum of the calcium hydroxide radical (CaOH) in its X 2-SIGMA+ (upsilon = 0) ground state has been observed in the laboratory using millimeter/submillimeter direct absorption spectroscopy. CaOH was generated by the reaction of hydrogen peroxide with calcium vapor, produced in a Broida-type oven. Eleven rotational transitions of the species were measured in the range 80-320 GHz to an accuracy of +/- 50 kHz. The spin-rotation splitting was readily observed in these data. The magnetic hyperfine structure due to the proton spin, however, was sufficiently small that it could not be resolved. The rotational and spin-rotation constants of CaOH were determined from a nonlinear least-squares fit to the data, using a 2-SIGMA Hamiltonian. These laboratory measurements will now allow for an in-depth radio astronomical search for CaOH in interstellar clouds and circumstellar envelopes of late-type stars.