1. INTRODUCTION
1.2. H₃⁺ as an Astrophysical Probe

2. OBSERVATIONS

3. DATA REDUCTION

4. RESULTS
4.2. H₃⁺ equivalent widths and column densities
4.3. Temperature and Density

5. DISCUSSION
5.1. The Ionization Rate
5.2. The Case of Large L in the CMZ
5.3. The Case of High ζ in the CMZ
5.4. The +50 km s⁻¹ absorption toward GC IRS 3
5.5. Infrared pumping

6. SUMMARY POINTS