  We present the results of ground-based imaging spectroscopy of the [Ne II]
12.8 micron line emitted from the ultracompact (UC) H II regions; W51d,
G45.12+0.13, G35.20-1.74 and Monoceros R2, with 2arcsec spatial resolution. We
found that the overall distribution of the [Ne II] emission is generally in
good agreement with the radio (5 or 15 GHz) VLA distribution for each source.
The Ne+ abundance ([Ne+/H+]) distributions are also derived from the [Ne II]
and the radio maps. As for G45.12+0.13 and W51d, the Ne+ abundance decreases
steeply from the outer part of the map toward the radio peak. On the other
hand, the Ne+ abundance distributions of G35.20-1.74 and Mon R2 appear rather
uniform. These results can be interpreted by the variation of ionizing
structures of neon, which is primarily determined by the spectral type of the
ionizing stars. We have evaluated the effective temperature of the ionizing
star by comparing the Ne+ abundance averaged over the whole observed region
with that calculated by H II region models based on recent non-LTE stellar
atmosphere models: 39,100 (+1100, -500) K (O7.5V-O8V) for W51d, 37,200 (+1000,
-700) K (O8V-O8.5V) for G45.12+0.13, 35,000-37,600 (+1500, -600) K (O8V-O9V)
for G35.20-1.74, and < 34,000 K (< B0V) for Mon R2. These effective
temperatures are consistent with those inferred from the observed Ne+ abundance
distributions.
