The microwave spectrum of the rubidium monoxide RbO radical

The rotational spectra of 85RbO in the ground- and the first excited vibrational states and of 87RbO in the ground vibrational state were observed in the millimeter- and submillimeter-wave region. The RbO radical was generated in a high-temperature absorption cell by the reaction of N2O with Rb vapor, which was produced in the cell by heating a mixture of RbCl and lithium metal to 500–550 °C. Analysis of the observed spectra yielded the rotational and centrifugal distortion constants, spin–rotation interaction constants, and hyperfine interaction constants. The bond length and the vibrational frequency were calculated from the rotational and centrifugal distortion constants to be 2.254 193 1 (15) A and 387.22 (20) cm−1, respectively, for 85RbO. The ground electronic state of RbO was confirmed to be 2Σ, and the low-lying 2Π state was estimated to be located at 650–700 cm−1 above the ground state by using a second-order perturbation expression with the vibrational energy in the denominator for the spin–rota...