Description:
<jats:p>Cesium bihalide salts, probably ClHCl−, ClDCl−, ClHBr−, ClHl−, and ClDl−, have been prepared and sharp infrared spectra obtained at 20°K. In addition, complex spectra which must be attributed to higher polymers such as H2Cl3− have been obtained. The 20°K infrared spectra of the cesium bihalide salts reveal an absorption at roughly half the frequency earlier assigned to ν2 for NR4+XHY− salts at room temperature. This requires a reinterpretation of the earlier bihalide spectra; the bands previously assigned to ν2 must be assigned instead to 2ν2. This reassignment obviates difficulties with previous assignments but requires an explanation for the high 2ν2 intensities. These can be explained in terms of the abnormally large dipole second derivative which occurs in hydrogen bonds because of the large charge mobility along the bond. In ClHCl− the occurrence of this enhancement shows that ClHCl− does not involve a centrally located proton in the cesium salt.</jats:p>