SiH and the Unidentified 4.6 Micron Feature

Results from experimental studies of the irradiation of SiH₄-H₂O and Fe(CO)₅-SiH₄-H₂O ice mixtures at 15K using 1 MeV protons have revealed the synthesis of a very stable infrared spectral feature at 4.6 μm which is characteristic of the SiH functional group. This feature persists through warmup of the ice, exposure to air at 300K, and vacuum annealing to at least 400K. Because of the high cosmic abundance of both silicon and hydrogen and the unexpected stability of the SiH feature in these experiments, the authors suggest that SiH might be responsible for the 4.6 μm absorption feature observed in W33A.