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We present a spectral line survey of the proto-planetary nebula AFGL 2688 inthe frequency ranges of 71-111 GHz, 157-160 GHz, and 218-267 GHz using theArizona Radio Observatory 12m telescope and the Heinrich Hertz SubmillimeterTelescope. A total of 143 individual spectral features associated with 32different molecular species and isotopologues were identified. The moleculesC3H, CH3CN, H2CO, H2CS, and HCO+ were detected for the first time in thisobject. By comparing the integrated line strengths of different transitions, weare able to determine the rotation temperatures, column densities, andfractional abundances of the detected molecules. The C, O, and N isotopicratios in AFGL 2688 are compared with those in IRC+10216 and the Sun, and werefound to be consistent with stellar nucleosynthesis theory. Through comparisonsof molecular line strengths in asymptotic giant branch stars, proto-planetarynebulae, and planetary nebulae, we discuss the evolution in circumstellarchemistry in the late stages of evolution.

A Molecular Line Survey of the Carbon-Rich Proto-Planetary Nebula AFGL 2688 in the 3mm and 1.3mm Windows