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The interstellar medium (ISM) seems to have a significant surplus of oxygenwhich was dubbed as the "O crisis": independent of the adopted interstellarreference abundance, the total number of O atoms depleted from the gas phasefar exceeds that tied up in solids by as much as ~160ppm of O/H. Recently, ithas been hypothesized that the missing O could be hidden in micrometer-sizedH2O ice grains. We examine this hypothesis by comparing the infrared (IR)extinction and far-IR emission arising from these grains with that observed inthe Galactic diffuse ISM. We find that it is possible for the diffuse ISM toaccommodate ~160ppm of O/H in micron-sized H2O ice grains without violating theobservational constraints including the absence of the 3.1micron O-H absorptionfeature. More specifically, H2O ice grains of radii ~4micron and O/H = 160 ppmare capable of accounting for the observed flat extinction at ~ 3-8 micron andproduce no excessive emission in the far-IR. These grains could be present inthe diffuse ISM through rapid exchange of material between dense molecularclouds where they form and diffuse clouds where they are destroyed byphotosputtering.

The Interstellar Oxygen Crisis, or Where Have All the Oxygen Atoms Gone?