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We present mid-infrared spectra and photometry from the Infrared Spectrographon the Spitzer Space Telescope for 51 OH megamasers (OHMs), along with 15galaxies confirmed to have no megamaser emission above L_OH = 10^2.3 L_sun. Themajority of galaxies display moderate-to-deep 9.7 um amorphous silicateabsorption, with OHM galaxies showing stronger average absorption and steeper20-30 um continuum emission than non-masing galaxies. Emission from multiplepolycyclic aromatic hydrocarbons (PAHs), especially at 6.2, 7.7, and 11.3 um,is detected in almost all systems. Fine-structure atomic emission (including[Ne II], [Ne III], [S III], and [S IV]) and multiple H2 rotational transitionsare observed in more than 90% of the sample. A subset of galaxies show emissionfrom rarer atomic lines, such as [Ne V], [O IV], and [Fe II]. 50% of the OHMsshow absorption from water ice and hydrogenated amorphous carbon grains (HACs),while absorption features from CO2, HCN, C2H2, and crystalline silicates arealso seen in several OHMs. Column densities of OH derived from 34.6 um OHabsorption are similar to those derived from 1667 MHz OH absorption innon-masing galaxies, indicating that the abundance of masing molecules issimilar for both samples. This data paper presents full mid-infrared spectrafor each galaxy, along with measurements of line fluxes and equivalent widths,absorption feature depths, and spectral indices.

Mid-infrared properties of OH megamaser host galaxies. I: Spitzer IRS low- and high-resolution spectroscopy