2012ApJ...748...95K

Studies of molecular hot cores and protostellar environments have shown that the observed abundance of gas-phase acetylene (C₂H₂) cannot be matched by chemical models without the inclusion of C₂H₂ molecules subliming from icy grain mantles. Searches for infrared (IR) spectral features of solid-phase acetylene are under way, but few laboratory reference spectra of C₂H₂ in icy mixtures, which are needed for spectral fits to observational data, have been published. Here, we report a systematic study of the IR spectra of condensed-phase pure acetylene and acetylene in ices dominated by carbon monoxide (CO), carbon dioxide (CO₂), methane (CH₄), and water (H₂O). We present new spectral data for these ices, including band positions and intrinsic band strengths. For each ice mixture and concentration, we also explore the dependence of acetylene's ν₅-band position (743/cm, 13.46 µm) and FWHM on temperature. Our results show that the ν₅feature is much more cleanly resolved in ices dominated by non-polar and low-polarity molecules, specifically CO, CO₂, and CH₄, than in mixtures dominated by H₂O-ice. We compare our laboratory ice spectra with observations of a quiescent region in Serpens.