Vibrationally Excited C${}_4$H

Abstract

Rotational spectra in four new excited vibrational levels of the linear carbon chain radical C${}_4$H 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 ${}^2{\Sigma }^{+}$ ground vibrational state of 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 tentatively assigned 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 $1{\nu }_5+1{\nu }_6$ 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 SMA near 257 GHz which show that C${}_4$H is present near the central star in IRC+10216. We found no evidence with the SMA for the new vibrationally excited levels of C${}_4$H at a peak flux density averaged over a $3^{\prime \prime }$ synthesized beam of $\ge 0.15$ 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.

The Astrophysical Journal Supplement Series, in press. 25 pages with 7 figures

References in corpus (4)

• Detection of C5N- and vibrationally excited C6H in IRC +10216
• Oxygen Chemistry in the Circumstellar Envelope of the Carbon-Rich Star IRC+10216
• A Detailed Analysis of the Dust Formation Zone of IRC+10216 Derived from Mid-IR Bands of C2H2 and HCN
• Density-enhanced gas and dust shells in a new chemical model for IRC+10216

Cited by in corpus (2)

• Carbon chemistry in IRC+10216: Infrared detection of diacetylene
• Monitor variability of millimeter lines in IRC +10216