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 K=1 components of the 12K-11K, 13K-12K, 14K-13K, 15K-14K, and 16K-15K transitions were observed. Consistent with an ?10 K kinetic temperature for the TMC-1 dark dust cloud, no higher K components were detected. The CH3C5N 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 methycyanoacetylene (CH3C3N). The abundance ratio of CH3C5N to CH3C3N is in the range of 0.5 to 1, but most probably closer to 0.5 than 1. Methyl cyanide (CH3CN), CH3C3N, and CH3C5N are all found in TMC-1 in decreasing relative abundance, suggesting that simple carbon addition on grains may be possible even in dark clouds.
Citation: Astrophysical Journal
Pub Type: Journals
abundances, clouds, cyanides, microwave spectrum, molecules, radio astronomy