A SURVEY OF MOLECULAR LINES TOWARD MASSIVE CLUMPS IN EARLY EVOLUTIONARY STAGES OF HIGH-MASS STAR FORMATION

We have observed the CH3OH J = 2-1, SiO J = 2-1, (CS)-S-34 J = 2-1, (HCO+)-C-13 J = 1-0, (HNC)-C-13 J = 1-0, CCH N = 1-0, OCS J = 8-7, and SO J(N) = 2(2)-1(1) lines toward 20 massive clumps, including Midcourse Space Experiment (MSX) 8 mu m dark sources (infrared dark clouds) and MSX 8 mu m sources, by using the Nobeyama Radio Observatory 45 m telescope. We have found that the velocity widths of the CH3OH and (CS)-S-34 lines are broader than those of the (HCO+)-C-13 line in the MSX dark sources. On the other hand, they are comparable to the velocity width of the (HCO+)-C-13 line in the MSX sources. In addition, the [SiO]/[(HCO+)-C-13] abundance ratio is found to be enhanced in the MSX dark sources in comparison with the MSX sources. These results suggest that shocks caused by interaction between an outflow and an ambient dense gas would have substantial impact on the chemical composition of the MSX dark sources. The velocity widths of the CH3OH and (CS)-S-34 lines relative to that of the (HCO+)-C-13 line as well as the [SiO]/[(HCO+)-C-13] abundance ratio could be used as good tools for investigating evolutionary stages of massive clumps. On the basis of the results, we discuss the chemical and physical evolution of massive clumps.