PRESSURE-SCANNED FERMI RESONANCES IN THE VIBRATIONAL-SPECTRA OF THE SULFATE ION

The pressure-scanning of spectra is recommended as a valuable extra spectroscopic technique, which can help to resolve ambiguities in band assignments and can also provide valuable extra information on weak but important transitions. Two specific examples are used to illustrate the method: firstly a clearly resolved resonance in the SO stretching region of KBr/CaSO4 is shown, and secondly a poorly resolved resonance in the KI/CaSO4 spectrum is used to show how, even in such a case, a considerable amount of extra information can be deduced. In both resonances the weak component was identified as a combination band involving a gap-mode, and the results obtained from analyses of the pressure scanned spectra are as follows: KBr/CaSO4 there is a gap mode of frequency 97.0±0.5 cm-1 for which dνg/dp=0.88±0.04 cm-1 (k bar)-1 and the potential energy term coupling (ν1 + νg) and ν3b1 is δ1g3b1=2.10±0.03 cm-1, and for KI/CaSO4 νg=78.7±0.7 cm-1 dνg/dp=0.92±0.08 cm-1 (k bar)-1 and δ3b1g3a1=2.8±0.2 cm-1 at 80 K and zero pressure. © 1979.