CONFIRMATION OF INTERSTELLAR METHYLCYANODIACETYLENE
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Publisher:Ohio State University
Ten spectral lines of the symmetric top molecule methylcyanodiacetylene (CH$_3$C$_5$N) have been detected with the 100-m Green Bank Telescope (GBT) toward the Taurus molecular cloud TMC-1. Both K=0 and K=1 components of the 12,K-11,K, 13,K-12,K, 14,K-13,K, 15,K-14,K, and 16,K-15,K transitions were observed. Consistent with $\sim$10 K kinetic temperature for the TMC-1 dark dust cloud, no higher K components were detected. The CH$_3$C$_5$N excitation temperature range is 2.7 K to 4.0 K for both K=0 and K=1 ladders, similar to that previously reported for methylcyanoacetylene (CH$_3$C$_3$N). The abundance ratio of CH$_3$C$_5$N to CH$_3$C$_3$N is in the range of 0.5 to 1, but most probably closer to $\sim$0.5 than 1. Methyl cyanide (CH$_3$CN), CH$_3$C$_3$N, and CH$_3$C$_5$N are all found in TMC-1 in decreasing relative abundance, suggesting that simple carbon addition may be possible in dark clouds.
Author Institution: Department of Astronomy, University of Illinois, 1002 W.; Green Street, Urbana, IL 61801; NASA Goddard Space Flight Center, Space and Earth Data; Computing Division, Code 930, Greenbelt, MD 20771; National Radio Astronomy Observatory, P. O. Box 2,; Green Bank, WV 24944-0002; Optical Technology Division, National Institute of Standards; and Technology, Gaithersburg, MD 20899; NASA Goddard Space Flight Center, Space and Earth Data; Computing Division, Code 930, Greenbelt, MD 20771; National; Research Council Resident Research Associate