Spectra of the Alkali Halides. II. The Infrared Spectra of the Sodium and Potassium Halides, RbCl, and CsCl

The infrared spectra of NaCl, NaBr, NaI, KCl, KBr, RbCl, CsCl in the gas phase have been measured in the region of the fundamental vibration frequency. The vibrational frequencies calculated from the observed spectra are: NaCl ωe=366 cm−1,NaBr ωe=302 cm−1,NaI ωe=258 cm−1,KCl ωe=281 cm−1,KBr ωe=213 cm−1,RbCl ωe=228 cm−1,CsCl ωe=209 cm−1.This data, together with previous data on the lithium halides, permits extrapolations to be made to determine the vibrational frequencies of the following halides: KI ωe=173 cm−1,RbBr ωe=166 cm−1,RbI ωe=128 cm−1,CsBr ωe=139 cm−1,CsI ωe=101 cm−1.The classical ionic model for the gaseous alkali halides is found to be in quantitative agreement with experiment. Some aspects of the problem of dimers in the gas phase are discussed.