  We present a study of ro-vibrational OH and CO emission from 21 disks around
Herbig Ae/Be stars. We find that the OH and CO luminosities are proportional
over a wide range of stellar ultraviolet luminosities. The OH and CO line
profiles are also similar, indicating that they arise from roughly the same
radial region of the disk. The CO and OH emission are both correlated with the
far-ultraviolet luminosity of the stars, while the PAH luminosity is correlated
with the longer wavelength ultraviolet luminosity of the stars. Although disk
flaring affects the PAH luminosity, it is not a factor in the luminosity of the
OH and CO emission. These properties are consistent with models of
UV-irradiated disk atmospheres. We also find that the transition disks in our
sample, which have large optically thin inner regions, have lower OH and CO
luminosities than non-transition disk sources with similar ultraviolet
luminosities. This result, while tentative given the small sample size, is
consistent with the interpretation that transition disks lack a gaseous disk
close to the star.
