Deuterated molecules in Orion KL from Herschel/HIFI
  We present a comprehensive study of the deuterated molecules detected in the
fullband HIFI survey of the Orion KL region. Ammonia, formaldehyde, and
methanol and their singly deuterated isotopologues are each detected through
numerous transitions in this survey with a wide range in optical depths and
excitation conditions. In conjunction with a recent study of the abundance of
HDO and H$_2$O in Orion KL, this study yields the best constraints on deuterium
fractionation in an interstellar molecular cloud to date. As previous studies
have found, both the Hot Core and Compact Ridge regions within Orion KL contain
significant abundances of deuterated molecules, suggesting an origin in cold
grain mantles. In the Hot Core, we find that ammonia is roughly a factor of 2
more fractionated than water. In the Compact Ridge, meanwhile, we find similar
deuterium fractionation in water, formaldehyde, and methanol, with D/H ratios
of (2---8) $\times$ $10^{-3}$. The [CH$_2$DOH]/[CH$_3$OD] ratio in the Compact
Ridge is found to be $1.2 \pm 0.3$. The Hot Core generally has lower deuterium
fractionation than the Compact Ridge, suggesting a slightly warmer origin, or a
greater contribution from warm gas phase chemistry.
