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Analysis of the infrared Fe II line strengths in NGC 4151 indicates that the electron density is 3.8 < log(Ne) < 4.25 and the electron temperature is 8000 < Te < 10,000 K in the narrow line emission region. The analysis utilizes the new collision strengths calculate by Pradhan and Zhang (1993, Ap.J. Letters, 409, L77) for the infrared lines. The line strengths are taken from new spectra between 0.88 and 2.5 microns with the GRIS spectrometer and from earlier work of Osterbrock, Shaw, and Veilleux (1990 Ap.J. 352, 561). The infrared Fe II lines have the advantage of critical densities in the range of log(Ne) ~ 5, a large separation between lines, and greatly reduced extinction. The new infrared spectrum has the additional advantage of a consistent spectrum in time, aperture, and resolution over a large number of lines. For a typical AGN iron to hydrogen ratio the ratio of Fe II emission to Paschen Beta indicates that approximately 10% of the iron in NGC 4151 is in the form of Fe II. Comparision with typical H II region results show that significant grain destruction has occurred in the emission region.
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