Upper limits for the ethyl-cyanide abundances in TMC-1 and L134N: Chemical implications

We have sought interstellar ethyl-cyanide via its 2₀₂–1₀₁ transition towards two cold, dark clouds and report upper limits of the total column densities of 3×10¹²cm^–2 and 2×10¹²cm^–2 for TMC-1 and L134N, respectively. We also observed the 2₀₂–1₀₁ transition of vinyl cyanide previously identified in TMC-1 by Matthews and Sears (1983b). The detection of vinyl cyanide and the non-detection of ethyl cyanide in TMC-1 are consistent with gas phase ion-molecule chemical models, and there is thus no necessity of invoking grain surface synthesis for vinyl cyanide in cold clouds.