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Certain planetary nebulae contain shells, filaments, or globules of cold gasand dust whose heating and chemistry are likely driven by UV and X-ray emissionfrom their central stars and from wind-collision-generated shocks. We presentthe results of a survey of molecular line emission in the 88-236 GHz range fromnine nearby (<1.5 kpc) planetary nebulae spanning a range of UV and X-rayluminosities, using the 30 m telescope of the Institut de RadioastronomieMillimetrique. Rotational transitions of thirteen molecules, including COisotopologues and chemically important trace species, were observed and theresults compared with and augmented by previous studies of molecular gas inPNe. Lines of the molecules HCO+, HNC, HCN, and CN, which were detected in mostobjects, represent new detections for five planetary nebulae in our study.Specifically, we present the first detections of 13CO (1-0, 2-1), HCO+, CN,HCN, and HNC in NGC 6445; HCO+ in BD+303639; 13CO (2-1), CN, HCN, and HNC inNGC 6853; and 13CO (2-1) and CN in NGC 6772. Flux ratios were analyzed toidentify correlations between the central star and/or nebular UV and X-rayluminosities and the molecular chemistries of the nebulae. This analysisreveals a surprisingly robust dependence of the HNC/HCN line ratio on PNcentral star UV luminosity. There exists no such clear correlation between PNX-rays and various diagnostics of PN molecular chemistry. The correlationbetween HNC/HCN ratio and central star UV luminosity demonstrates the potentialof molecular emission line studies of PNe for improving our understanding ofthe role that high-energy radiation plays in the heating and chemistry ofphotodissociation regions.

A New Radio Molecular Line Survey of Planetary Nebulae: HNC/HCN as a Diagnostic of Ultraviolet Irradiation