Pressure-Scanned Fermi Resonance in the Spectrum of NH4+ Isolated in CsBr

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By using sample pressures up to 50 kbar at a temperature of 100°K, two energy levels of the same symmetry in the NH4+ in CsBr vibrational system have been scanned through the region of maximum Fermi resonance, (i.e., the “cross-over” region). This experiment shows unambiguously the observed results of continuously varying the coupling between the two resonating levels. Not only do these results afford an improved insight into the phenomenon of Fermi resonance itself, but they also illustrate the value of pressure scanning as a means of resolving detailed interpretational difficulties.