1996A&A...306L..21L

Calculations are reported of the molecular abundances in a cloud subjected to varying ionizing fluxes and attention is drawn to the molecules which survive as the intensity is increased. The calculations support the suggestion of Phillips & Lazio (1995) that the absence of HCO+ near the hard X-ray source 1E1740.7-2942 may be due to a high X-ray flux. The calculations also raise the possibility that the anomalous HCN/CO ratio observed in the Seyfert Galaxy NGC 1068 may be a consequence of X-ray ionization. High abundances are predicted for CN and NO. Observations of these may serve to distinguish between the different scenarios.