  We present analysis of archival data from multiple XMM-Newton observations of
the Seyfert 1 galaxy NGC 4151. Spectral data from the RGS instruments reveal
several strong soft X-ray emission lines, chiefly from hydrogen-like and
helium-like oxygen, nitrogen, neon and carbon. Radiative recombination continua
(RRC) from oxygen and carbon are also detected. Our analysis suggests that the
emission data are consistent with photoionization. Using the CLOUDY
photoionization code, we found that, while a two-component, high column density
model (10e23 cm-2) with low covering factor proved adequate in reproducing all
detected Lyman series lines, it proved insufficient in modeling He-like
triplets observed (neon, oxygen, and nitrogen). If resonance line data were
ignored, the two-component model was sufficient to match flux from
intercombination and forbidden lines. However, with the inclusion of resonance
line data, He-like triplets could no longer be modeled with only two
components. We found that observed oxygen G and R ratios especially were
anomalous in parameter space investigated. We investigated, and were forced to
dismiss, the possibility that a third purely collisional component could be
responsible for enhanced resonance line contributions. We succeeded in modeling
the observed spectrum with the addition of a third, lower column density
(10e20.5 cm-2) component with non-zero microturbulence and high covering
factor. While sufficient to reproduce observed soft X-ray flux, our model faces
certain shortcomings, particularly in a less-than-ideal visual fit to the line
profile. Two of the three emission model components bear similarities to
components determined by Kraemer et al. (2005) in their study of NGC 4151
absorption spectra.
