Knowledge Bank

Cyanide compounds are quite abundant and occur in great variety in the interstellar medium. During the past several years, the molecules CN, $HCN,C3N,HC3N,HC5N, CH3CN$ and $CH2CHCN$ have been detected in interstellar sources. We now report the detection of an even larger cyanide compound, ethylcyanide $(C2H5CN)$. Independent astronomical observations by P. Thaddeus and M. Guelin (Goddard Institute for Space Studies) and C. A. Gottlieb, E. W. Gottlieb, and M. M. Litvak (Harvard College Observatory) have resulted in the detection of twenty-four transitions from Orion A and seven transitions from Sgr B2. Ethylcyanide has been convincingly established as the source of these lines by fitting these observations with the millimeter-wave laboratory spectrum. The analysis shows that the ethylcyanide cloud in Orion occurs at a velocity of $+4.5\pm 1 km s-1$ which is significantly lower than the typical velocity of $8.5 km s-1$ for most molecules. Details of the laboratory analysis, astronomical observations and, where possible, a comparison of the densities of various interstellar cyanides will be presented.