A Spectral Line Survey in the 2 and 1.3 mm Windows toward the Carbon‐rich Envelope of IRC +10216

We present the results of our spectral line surveys in the 1.3 and 2 mm windows toward the carbon-rich envelope of IRC +10216. There were 377 lines are detected in total, of which 360 lines are assigned to 57 known molecules (including 29 rare isotopomers and two cyclic isomers). Only 17 weak lines remain unidentified. Rotational lines of isotopomers 13 CCH and HN 13 C are detected for the first time in IRC +10216 . The detection of the formaldehyde lines in this star is also confirmed. Possible abundance differences among the three 13 C-substituted isotopic isomers of HC 3 N is reported. Isotopic ratios of C and O are confirmed to be nonsolar while those of S and Si to be nearly solar. Column densities have been estimated for 15 molecular species. Modified spectroscopic parameters have been calculated for NaCN, Na 13 CN, KCN, and SiC 2 . Transition frequencies from the present observations were used to improve the spectroscopic parameters of Si 13 CC, 29 SiC 2 , and 30 SiC 2 .