The rotational spectra of (RbO)-Rb-85 in the ground-and the first excited v
ibrational states and of (RbO)-Rb-87 in the ground vibrational state were o
bserved in the millimeter- and submillimeter-wave region. The RbO radical w
as generated in a high-temperature absorption cell by the reaction of N2O w
ith Rb vapor, which was produced in the cell by heating a mixture of RbCl a
nd lithium metal to 500-550 degrees C. Analysis of the observed spectra yie
lded the rotational and centrifugal distortion constants, spin-rotation int
eraction constants, and hyperfine interaction constants. The bond length an
d the vibrational frequency were calculated from the rotational and centrif
ugal distortion constants to be 2.254 193 1 (15) Angstrom and 387.22 (20) c
m(-1), respectively, for (RbO)-Rb-85. The ground electronic state of RbO wa
s confirmed to be (2)Sigma, and the low-lying (2)Pi 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-rotation interaction constant. The observed hyperfine interaction
constants indicated that the RbO radical is essentially an ionic molecule.
(C) 1999 American Institute of Physics. [S0021-9606(99)01306-9].