The pure rotational spectra of ZrO and ZrS have been recorded using cavity
Fourier transform microwave spectroscopy in the frequency range 9-26 GHz. T
he molecules were generated by laser ablation of a solid Zr rod in the pres
ence of 0.05% of O-2 or H2S, respectively, in either argon or neon. Rotatio
nal spectra of five previously unobserved isotopomers of ZrO in the X(1)Sig
ma(+) state have been measured. Spectra for all five (ZrS)-S-32 isotopomers
and for the (ZrS)-Zr-90-S-34 isotopomer in natural abundance have also bee
n measured; this is the first report of pure rotational transitions for ZrS
. Transitions in several excited vibrational states were also measured for
the most abundant isotopomers of both species. Atomic mass-dependent Born-O
ppenheimer breakdown correction terms were determined by fitting the data o
btained for each molecule to a Dunham-like expression. Values for the equil
ibrium bond lengths of the two species were also calculated from the result
s of these fits. For both the (ZrS)-Zr-91-S-32 and (ZrO)-Zr-91-O-16 isotopo
mers, nuclear hyperfine structure due to the zirconium nucleus was observed
and values for eQ(q0) (Zr-91) and C-I (Zr-91) have been determined. A rota
tional transition in the low lying a (3)Delta state of ZrS has also been ob
served. (C) 1999 American Institute of Physics. [S0021-9606(99)00121-X].