Vibrationally Excited C₄H

الأصل · EN

Rotational spectra in four new excited vibrational levels of the linear carbon chain radical C₄H radical 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 ²Σ+ ground vibrational state of C₄H and were assigned to new bending vibrational levels, two each with ²Σ and ²Π vibrational symmetry. The new levels are tentatively assigned to the 1ν₆ and 1ν₅ bending vibrational modes (both with ²Π symmetry), and the 1ν₆ + 1ν₇ and 1ν₅ + 1ν₆ combination levels (²Σ 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 1ν₇ and 2ν₇ levels were refined. Also presented are interferometric maps of the ground state and the 1ν₇ level obtained with the 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.