Chemical and physical evolution of dark clouds Molecular spectral line survey toward TMC-1

Abstract

Interstellar dark clouds are known as the source of star and planetary system formation, and the study of chemical composition in dark clouds is important for understanding the process of evolution of matter in the universe toward the planets and to life. The results of the first molecular spectral line survey toward a typical dark cloud, TMC-1 (Taurus Molecular Cloud-1) have been reported. The observations were completed in the frequency range 8800–50000 MHz, and the results of detailed data analysis are presented. This is the first complete spectral line survey toward a cold, dark cloud ever made. We used the 45 m mm-wave telescope and a very large acousto-optical radiospectrometer with 32000 output channels of the Nobeyama Radio Observatory, NAOJ. We detected 404 lines from 38 molecules including 11 new molecules such as C₆H, CCO, CCCO, CCS, CCCS, HNCCC, HCCNC, HCCCNH⁺, HCCCHO, CH₂CN and cyclic C₃H, all of them are short-lived organic compounds unknown before our detection. We also detected three new isotopomers, CC³⁴S, CCC³⁴S and HDCS. These results provide the basic general composition of cold, dark clouds for the first time. We also discuss chemical and physical evolution of dark clouds.