Six H ii regions at galactocentric distances of R ¼ 10 15 kpc have been observed in the far-IR emission lines of [O iii] (52 m, 88 m), [ N iii] (57 m), and [S iii] (19 m) using the Kuiper Airborne Observatory. These observations have been combined with Very Large Array radio continuum observations of these sources to determine the abundances of O ++ , N ++ , and S ++ relative to hydrogen. In addition, eight of the most recent sets of measurements of ionic line strengths in H ii regions have been reanalyzed in order to attempt to reconcile differences in optical versus far-IR abundance determinations. We have in total 168 sets of observations of 117 H ii regions in our analysis. The new analysis included updating the atomic constants (transition probabilities and collision cross sections), recalculation of some of the physical conditions in the H ii regions (n e and T e), and the use of new photoionization models to determine stellar effective temperatures of the exciting stars. We also use the most recent data available for the distances for these objects, although for most we still rely on kinematic distance determinations. Our analysis finds little indication of differences between optical and infrared observations of the nitrogen abundances, but some differences are seen in the oxygen and sulfur abundances. A very significant offset continues to be seen between optical and infrared measurements of the N/O abundance ratio.

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We present Spitzer IRS spectra (R ∼ 600, 10 -38 µm) of 38 positions in the Galactic Center (GC), all at the same Galactic longitude and spanning ±0.3 • in latitude. Our positions include the Arches Cluster, the Arched Filaments, regions near the Quintuplet Cluster, the "Bubble" lying along the same line-ofsight as the molecular cloud G0.11−0.11, and the diffuse interstellar gas along the line-of-sight at higher Galactic latitudes. From measurements of the, and H 2 S(0), S(1), and S(2) lines we determine the gas excitation and ionic abundance ratios. The Ne/H and S/H abundance ratios are ∼ 1.6 times that of the Orion Nebula. The main source of excitation is photoionization, with the Arches Cluster ionizing the Arched Filaments and the Quintuplet Cluster ionizing the gas nearby and at lower Galactic latitudes including the far side of the Bubble. In addition, strong shocks ionize gas to O +3 and destroy dust grains, releasing iron into the gas phase (Fe/H∼ 1.3 × 10 −6 in the Arched Filaments and Fe/H∼ 8.8 × 10 −6 in the Bubble). The shock effects are particularly noticeable in the center of the Bubble, but O +3 is present in all positions. We suggest that the shocks are due to the winds from the Quintuplet Cluster Wolf-Rayet stars. On the other hand, the H 2 line ratios can be explained with multi-component models of warm molecular gas in photodissociation regions without the need for H 2 production in shocks.

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