Spectroscopic detection of the 3.934 Micron line of Si IX in the solar corona

We report the detection of the 2s² 2p^{2 3}P_1→0 line of Si ix using the McMath-Pierce telescope on Kitt Peak. Observations were made of the solar disk and at various heights above the limb between 2002 May 13 and 17, under nonideal sky conditions, using the 13.5 m vertical spectrograph and an InSb single-diode detector. We report a new rest wavelength for the line and discuss its potential use as a diagnostic of coronal magnetic fields using ground-based telescopes. Our observations give λ_rest = 3.93434 ± 0.00007 μm, consistent with earlier less accurate values, but it places the blue wing of the line under a strong telluric N₂O line. In the active regions observed, the line's intensity is comparable to or larger than predicted in earlier work for the quiet Sun.