Water in Protoplanetary Disks: Deuteration and Turbulent Mixing
  We investigate water and deuterated water chemistry in turbulent
protoplanetary disks. Chemical rate equations are solved with the diffusion
term, mimicking turbulent mixing in vertical direction. Water near the midplane
is transported to the disk atmosphere by turbulence and destroyed by
photoreactions to produce atomic oxygen, while the atomic oxygen is transported
to the midplane and reforms water and/or other molecules. We find that this
cycle significantly decreases column densities of water ice at r < 30 AU, where
dust temperatures are too high to reform water ice effectively. The radial
extent of such region depends on the desorption energy of atomic hydrogen. Our
model indicates that water ice could be deficient even outside the sublimation
radius. Outside this radius, the cycle decreases the D/H ratio of water ice
from 2x10^-2, which is set by the collapsing core model, to 10^-4-10^-2 in 10^6
yr, without significantly decreasing the water ice column density. The
resultant D/H ratios depend on the strength of mixing and the radial distance
from the central star. Our finding suggests that the D/H ratio of cometary
water (10^-3-10^-4) could be established (i.e. cometary water could be formed)
in the solar nebula, even if the D/H ratio of water ice delivered to the disk
was very high (10^-2).
