  Molecular line observations that could resolve protoplanetary disks of ~100
AU both spatially and kinematically would be a useful tool to unambiguously
identify these disks and to determine their kinematical and physical
characteristics. In this work we model the expected line emission from a
protoplanetary disk irradiated by an infalling envelope, addressing the
question of its detectability with subarcsecond resolution. We adopt a
previously determined disk model structure that gives a continuum spectral
energy distribution and a mm intensity spatial distribution that are consistent
with observational constraints of HL Tau. An analysis of the capability of
presently working and projected interferometers at mm and submm wavelengths
shows that molecular transitions of moderate opacity at these wavelengths
(e.g., C17O lines) are good candidates for detecting disk lines at subarcsecond
resolution in the near future. We suggest that, in general, disks of typical
Class I sources will be detectable.
