A Survey of Large Molecules toward the Proto–Planetary Nebula CRL 618

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 (CH 3 CHO), acetic acid (CH 3 COOH), dimethyl ether (CH 3 OCH 3 ), ethanol (CH 3 CH 2 OH), formic acid (HCOOH) and methyl formate (HCOOCH 3 ); large carbon chain molecules including methyl cyanide (CH 3 CN), methylcyanoacetylene (CH 3 C 3 N), cyanoacetylene (HC 3 N), cyanodiacetylene (HC 5 N), and C 6 H; and, finally, smaller molecules including 34 SO, SO 2 , OC 34 S, and MgNC. No biologically important organic molecules were detected. However, we report the first interferometric detections of CH 3 CN and vibrationally excited HC 3 N and HC 5 N toward this source. The temperature and distribution of CH 3 CN 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 HC 5 N support its distribution in the extended envelope expanding radially from the central star. The detection of vibrationally excited HC 3 N confirmed the temperature structure and column density of HC 3 N 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.