CMB experiments commonly use maps of Ha intensity as a spatial template for Galactic free-free emission, assuming a power law I_v ∝ v~(-0.15) for the spectrum. Any departure from the assumed free-free spectrum could have a detrimental effect on determination of the primary CMB anisotropy. We show that the Hα-correlated emission spectrum in the diffuse WIM is not the expected free-free spectrum at WMAP frequencies. Instead, there is a broad bump in the spectrum at ～50 GHz which is consistent with emission from spinning dust grains. Spectra from both the full sky and smaller regions of interest are well fit by a superposition of a free-free and " warm ionized medium " Draine & Lazarian spinning dust model, shifted in frequency. The spinning dust emission is ～5 times weaker than the free-free component at 50 GHz, with the null hypothesis that the Hα-correlated spectrum is pure free-free ruled out at ≥8 σ in all regions and > 100 σ for the full-sky fit.
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