A SPECTRAL-LINE SURVEY OF IRC+10216 AT MILLIMETER AND SUBMILLIMETER WAVELENGTHS

The James Clerk Maxwell Telescope has been used to carry out a spectral line survey of IRC +10216. The frequency coverage spans the interval from 339.6 to 364.6 GHz plus a range of 14.2 GHz distributed noncontiguously between 222.4 and 267.9 GHz. A total of 46 spectral lines were detected from 11 different identified molecules and isotopomers, and an additional eight weak features are unidentified. The integrated line flux density within the 850 mu atmospheric window exceeds that due to broad-band dust emission in this source. Eleven lines of SiCC have been observed with excitation energies from 70 to 330 K above the ground state. The excitation temperatures measured between different K(a) ladders of SiCC range from 145 to 227 K, suggesting that excitation by infrared radiation is important for this molecule. The total column density of SiCC is found to be 2.8 X 10(15) cm-2. Abundances of CN, C2H, C4H and SiS are estimated to be 7.6 X 10(14), 5.4 X 10(15), 5.6 X 10(15), and 6.5 X 10(15) cm-2, respectively.