VIBRATIONALLY EXCITED C4H

Rotational spectra in four new excited vibrational levels of the linear carbon chain radical C4H were observed in the millimeter band between 69 and 364 GHz in a low pressure glow discharge, and two of these were observed in a supersonic molecular beam between 19 and 38 GHz. All have rotational constants within 0.4% of the X-2 Sigma(+) ground vibrational state of C4H and were assigned to new bending vibrational levels, two each with (2)Sigma and (2)Pi vibrational symmetry. The new levels are tentatively assigned to the 1 nu(6) and 1 nu(5) bending vibrational modes (both with (2)Pi symmetry), and the1 nu(6) + 1 nu(7) and 1 nu(5) + 1 nu(6) combination levels ((2)Sigma symmetry) on the basis of the derived spectroscopic constants, relative intensities in our discharge source, and published laser spectroscopic and quantum calculations. Prior spectroscopic constants in the 1 nu(7) and 2 nu(7) levels were refined. Also presented are interferometric maps of the ground state and the 1 nu(7) level obtained with the Submillimeter Array (SMA) near 257 GHz which show that C4H is present near the central star in IRC+10216. We found no evidence with the SMA for the new vibrationally excited levels of C4H at a peak flux density averaged over a 3 '' synthesized beam of >= 0.15 Jy/beam in the 294-296 and 304-306 GHz range, but it is anticipated that rotational lines in the new levels might be observed in IRC+10216 when ALMA attains its full design capability.