  With the recent radioastronomical detection of cis-trans-carbonic acid
(H$_2$CO$_3$) in a molecular cloud toward the galactic center, the more stable
but currently unobserved cis-cis conformer is shown here to have strong IR
features. While the higher-energy cis-trans-carbonic acid was detected at
millimeter and centimeter wavelengths, owing to its larger dipole moment, the
vibrational structure of cis-cis-carbonic acid is more amenable to its
observation at micron wavelengths. Even so, both conformers have relatively
large IR intensities, and some of these fall in regions not dominated by
polycyclic aromatic hydrocarbons. Water features may inhibit observation near
the 2.75 $\mu$m hydride stretches, but other vibrational fundamentals and even
overtones in the 5.5 $\mu$m to 6.0 $\mu$m range may be discernible with JWST
data. This work has employed high-level, accurately benchmarked quantum
chemical anharmonic procedures to compute exceptionally accurate rotational
spectroscopic data compared to experiment. Such performance implies that the IR
absorption and even cascade emission spectral features computed in this work
should be accurate and will provide the needed reference for observation of
either carbonic acid conformer in various astronomical environments.
