Infrared spectra of complex organic molecules in astronomically relevant
  ice matrices. I. Acetaldehyde, ethanol, and dimethyl ether
  Context. The number of identified complex organic molecules (COMs) in inter-
and circumstellar gas-phase environments is steadily increasing. Recent
laboratory studies show that many such species form on icy dust grains. At
present only smaller molecular species have been directly identified in space
in the solid state. Accurate spectroscopic laboratory data of frozen COMs,
embedded in ice matrices containing ingredients related to their formation
scheme, are still largely lacking.
  Aims. This work provides infrared reference spectra of acetaldehyde
(CH$_3$CHO), ethanol (CH$_3$CH$_2$OH), and dimethyl ether (CH$_3$OCH$_3$)
recorded in a variety of ice environments and for astronomically relevant
temperatures, as needed to guide or interpret astronomical observations,
specifically for upcoming James Webb Space Telescope observations.
  Methods. Fourier transform transmission spectroscopy (500-4000 cm$^{-1}$ /
20-2.5 $\mu$m, 1.0 cm$^{-1}$ resolution) was used to investigate solid
acetaldehyde, ethanol and dimethyl ether, pure or mixed with water, CO,
methanol, or CO:methanol. These species were deposited on a cryogenically
cooled infrared transmissive window at 15~K. A heating ramp was applied, during
which IR spectra were recorded until all ice constituents were thermally
desorbed.
  Results. We present a large number of reference spectra that can be compared
with astronomical data. Accurate band positions and band widths are provided
for the studied ice mixtures and temperatures. Special efforts have been put
into those bands of each molecule that are best suited for identification. For
acetaldehyde the 7.427 and 5.803 $\mu$m bands are recommended, for ethanol the
11.36 and 7.240 $\mu$m bands are good candidates, and for dimethyl ether bands
at 9.141 and 8.011 $\mu$m can be used. All spectra are publicly available in
the Leiden Database for Ice.
