CH2D+, the Search for the Holy Grail
  CH2D+, the singly deuterated counterpart of CH3+, offers an alternative way
to mediate formation of deuterated species at temperatures of several tens of
K, as compared to the release of deuterated species from grains. We report a
longstanding observational search for this molecular ion, whose rotational
spectroscopy is not yet completely secure. We summarize the main spectroscopic
properties of this molecule and discuss the chemical network leading to the
formation of CH2D+, with explicit account of the ortho/para forms of H2, H3+
and CH3+. Astrochemical models support the presence of this molecular ion in
moderately warm environments at a marginal level.
