  Miniaturizing and integrating atomic vapor cells is widely investigated for
the purposes of fundamental measurements and technological applications such as
quantum sensing. Extending such platforms to the realm of molecular physics is
a fascinating prospect that paves the way for compact frequency metrology as
well as for exploring light-matter interactions with complex quantum objects.
Here, we perform molecular rovibrational spectroscopy in a thin-cell of
micrometric thickness, comparable to excitation wavelengths. We operate the
cell in two distinct regions of the electromagnetic spectrum, probing
$\nu_1$+$\nu_3$ resonances of acetylene at 1.530$\mu$m, within the
telecommunications wavelength range, as well as the $\nu_3$ and $\nu_2$
resonances of $SF_6$ and $NH_3$ respectively, in the mid-infrared fingerprint
region around 10.55$\mu$m. Thin-cell confinement allows linear sub-Doppler
transmission spectroscopy due to the coherent Dicke narrowing effect, here
demonstrated for molecular rovibrations. Our experiment can find applications
extending to the fields of compact molecular frequency references, atmospheric
physics or fundamental precision measurements.
