Detection of interstellar ethyl cyanide

Abstract

Twenty-four millimeter-wave emission lines of ethyl cyanide (CH3CH2CN) have been detected in the Orion Nebula (OMC-1) and seven in Sgr B2. To derive precise radial velocities from the astronomical data, the first laboratory measurement of the rotational spectrum of ethyl cyanide has been made at frequencies above 41 GHz. In OMC-1, the rotational temperature of ethyl cyanide is 90 K (in good agreement with other molecules), the local standard of rest radial velocity is 4.5 ± l.Okms-1 (versus 8.5kms _1 for most molecules), and the column density is 1.8 x 10 14 cm" 2 (a surprisingly high figure for a complicated molecule). The high abundance of ethyl cyanide in the Orion Nebula suggests that ethane and perhaps larger saturated hydrocarbons may be common constituents of molecular clouds and have escaped detection only because they are nonpolar, or only weakly so.