2006ApJ...647..412S

Ten spectral lines of the symmetric-top molecule methylcyanodiacetylene (CH₃C₅N) have been detected with the 100 m Green Bank Telescope (GBT) toward the Taurus molecular cloud TMC-1. Both K=0 and 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 ∼10 K kinetic temperature for the TMC-1 dark dust cloud, no higher K-components were detected. The CH₃C₅N spectra confirm an earlier identification report based on data obtained with the MPIfR 100 m telescope by Snyder and colleagues over 20 years ago. Methyl cyanide (CH₃CN), methylcyanoacetylene (CH₃C₃N), and methylcyanodiacetylene all are found in TMC-1 in decreasing relative abundance, suggesting that simple carbon addition on grains may be possible even in dark clouds. However, the correct formation mechanism for CH₃C₅N is still not known to within several orders of magnitude.