  We present an analysis of the mid-infrared spectra, obtained from the Spitzer
Space Telescope, of the dark globule, DC 314.8--5.1, which is at the onset of
low-mass star formation. The target has a serendipitous association with a
B-type field star, which illuminates a reflection nebula in the cloud. We focus
on the polycyclic aromatic hydrocarbon (PAH) emission features prevalent
throughout the mid-infrared range. The analysis of the spectra with the PAHFIT
software as well as pypahdb package, shows that (i) the intensities of PAH
features decrease over distance from the ionizing star toward the cloud center,
some however showing a saturation at larger distances; (ii) the relative
intensities of the 6.2 and 8.6 features with respect to the 11.2 micron feature
remain high throughout the globule, suggesting a larger cation-to-neutral PAH
ratio of the order of unity; the breakdown from pypahdb confirms a high ionized
fraction within the cloud; (iii) the pypahdb results display a decrease in
large PAH fraction with increased distance from HD 130079, as well as a
statistically significant correlation between the large size fraction and the
ionized fraction across the globule; (iv) the 7.7 PAH feature displays a peak
nearer to 7.8 microns, suggesting a chemically processed PAH population with a
small fraction of UV-processed PAHs; (v) the H2 S(0) line is detected at larger
distances from the ionizing star. All in all, our results suggest divergent
physical conditions within the quiescent cloud DC 314.8--5.1 as compared to
molecular clouds with ongoing starformation.
