Complex Organic Molecules in Taurus Molecular Cloud-1

We have observed the millimeter-wave rotational spectral lines of CH3CHO, H2CCO, cyclopropenone, and H2CO toward the cyanoployyne peak of Taurus Molecular Cloud-1 (TMC-1 CP). The spectral line profile of CH3CHO is found to reveal a well-separated double peak. It is similar to the line profile of CH3OH, but is much different from those of carbon-chain molecules and C34S. The different line profiles mean different distributions along the line of sight. The similarity of the spectral line profiles between CH3CHO and CH3OH suggests that CH3CHO is mainly formed on dust grains as CH3OH or through gas-phase reactions starting from CH3OH. On the other hand, the spectral line profiles of H2CCO and cyclopropenone are rather similar to those of carbon-chain molecules and C34S, implying their gas-phase productions. H2CO shows a composite spectral line profile reflecting the contributions of both gas-phase and grain-surface productions. In addition, we have detected the spectral lines of CH3CHO and HCOOCH3 toward the methanol peak near TMC-1 CP. We have also tentatively detected one line of (CH3)2O. Considering the chemical youth of TMC-1, the present results indicate that fairly complex organic species have already been formed in the early evolutionary phase of starless cores. TMC-1 is thus recognized as a novel source where formation processes of complex organic molecules can be studied on the basis of the line profiles.