2005ApJ...626..233R

We present the results of our survey toward the proto-planetary nebula CRL 618 for several large, highly saturated, oxygen-bearing organic molecules of biological importance including acetaldehyde (CH₃CHO), acetic acid (CH₃COOH), dimethyl ether (CH₃OCH₃), ethanol (CH₃CH₂OH), formic acid (HCOOH) and methyl formate (HCOOCH₃); large carbon chain molecules including methyl cyanide (CH₃CN), methylcyanoacetylene (CH₃C₃N), cyanoacetylene (HC₃N), cyanodiacetylene (HC₅N), and C₆H; and, finally, smaller molecules including ³⁴SO, SO₂, OC³⁴S, and MgNC. No biologically important organic molecules were detected. However, we report the first interferometric detections of CH₃CN and vibrationally excited HC₃N and HC₅N toward this source. The temperature and distribution of CH₃CN toward CRL 618 indicates that it is formed in the outer envelope surrounding the ultracompact H II region. Furthermore, the P Cygni line profile and corresponding channel maps of vibrationally excited HC₅N support its distribution in the extended envelope expanding radially from the central star. The detection of vibrationally excited HC₃N confirmed the temperature structure and column density of HC₃N in the inner envelope found by Wyrowski and colleagues. Finally, our observations clearly indicate that CRL 618 is a good source of large carbon chain species but a very poor source for detecting or producing organic species of biological importance.