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Rotational spectra in four new excited vibrational levels of the linearcarbon chain radical C$_4$H radical were observed in the millimeter bandbetween 69 and 364 GHz in a low pressure glow discharge, and two of these wereobserved in a supersonic molecular beam between 19 and 38 GHz. All haverotational constants within 0.4% of the $^2\Sigma^+$ ground vibrational stateof C$_4$H and were assigned to new bending vibrational levels, two each with$^2\Sigma$ and $^2\Pi$ vibrational symmetry. The new levels are tentativelyassigned to the $1\nu_6$ and $1\nu_5$ bending vibrational modes (both with$^2\Pi$ symmetry), and the $1\nu_6 + 1\nu_7$ and $1\nu_5 + 1\nu_6$ combinationlevels ($^2\Sigma$ symmetry) on the basis of the derived spectroscopicconstants, relative intensities in our discharge source, and published laserspectroscopic and quantum calculations. Prior spectroscopic constants in the$1\nu_7$ and $2\nu_7$ levels were refined. Also presented are interferometricmaps of the ground state and the $1\nu_7$ level obtained with the SMA near 257GHz which show that C$_4$H is present near the central star in IRC+10216. Wefound no evidence with the SMA for the new vibrationally excited levels ofC$_4$H at a peak flux density averaged over a $3^{\prime\prime}$ synthesizedbeam of $\ge 0.15$ Jy/beam in the 294-296 and 304-306 GHz range, but it isanticipated that rotational lines in the new levels might be observed inIRC+10216 when ALMA attains its full design capability.

Vibrationally Excited C$_4$H