The pure rotational spectrum of a(1) Delta(g) oxygen in its first exci
ted vibrational state as well as the ground vibrational state rotation
al spectra of (OO)-O-16-O-18 and O-18(2) in their a states have been o
bserved. Precise parameters describing the spectra have been determine
d and an accurate value has been derived for the equilibrium interatom
ic distance in the Born-Oppenheimer limit.