  We report on a search for Interstellar CH2D+. Four transitions occur in
easily accessible portions of the spectrum; we report on emission at the
frequencies of these transitions toward high column density star-forming
regions. While the observations can be interpreted as being consistent with a
detection of the molecule, further observations will be needed to secure that
identification. The CH2D+ rotational spectrum has not been measured to high
accuracy. Lines are weak, as the dipole moment induced by the inclusion of
deuterium in the molecule is small. Astronomical detection is favored by
observations toward strongly deuterium-fractionated sources. However, enhanced
deuteration is expected to be most significant at low temperatures. The
sparseness of the available spectrum and the low excitation in regions of high
fractionation make secure identification of CH2D+ difficult. Nonetheless, owing
to the importance of CH3+ to interstellar chemistry, and the lack of rotational
transitions of that molecule owing to its planar symmetric structure, a measure
of its abundance would provide key data to astrochemical models.
