  This work aims at characterizing the mid-IR spectra of formamide in its pure
form as well as in mixtures of the most abundant interstellar ices via
laboratory simulation of such ices, as well as demonstrating how these
laboratory spectra can be used to search for formamide in ice observations.
Mid-IR spectra (4000 - 500 cm$^{-1}$, 2.5 - 20 $\mu$m) of formamide, both in
its pure form as well as in binary and tertiary mixtures with H$_2$O, CO$_2$,
CO, NH$_3$, CH$_3$OH, H$_2$O:CO$_2$, H$_2$O:NH$_3$, CO:NH$_3$, and CO:CH$_3$OH,
are collected at temperatures ranging from 15 - 212 K. Apparent band strengths
and positions of eight IR bands of pure amorphous and crystalline formamide at
various temperatures are provided. Three bands are identified as potential
formamide tracers in observational ice spectra: the overlapping C=O stretch and
NH$_2$ scissor bands at 1700.3 and 1630.4 cm$^{-1}$ (5.881 and 6.133 $\mu$m),
the CH bend at 1388.1 cm$^{-1}$ (7.204 $\mu$m), and the CN stretch at 1328.1
cm$^{-1}$ (7.529 $\mu$m). The relative apparent band strengths, positions, and
FWHM of these features in mixtures at various temperatures are also determined.
Finally, the laboratory spectra are compared to observational spectra of low-
and high-mass young stellar objects as well as pre-stellar cores observed with
the Infrared Space Observatory, the Spitzer Space Telescope, and the JWST. A
comparison between the formamide CH bend in laboratory data and the 7.24 $\mu$m
band in the observations tentatively indicates that, if formamide ice is
contributing significantly to the observed absorption, it is more likely in a
polar matrix. Upper limits ranging from 0.35-5.1\% with respect to H$_{2}$O are
calculated. These upper limits are in agreement with gas-phase formamide
abundances and take into account the effect of a H$_{2}$O matrix on formamide's
band strengths.
