Knowledge Bank

Recent advances in nonlinear mixing technology have allowed us to obtain infrared spectra of the X$-$$.$H$2$O (X=F,Cl,Br) complexes in the 600-1800 cm$-$$1$ (16.7-5.6 $\mu$m) region. While transitions in this regime are typically associated with the three-dimensional confinement of the shared proton, unexpected spectral activity is observed. The out-of-plane vibrational overtone of the Cl$-$$.$H$2$O complex exhibits anomalous intensity, which is explained by a curvilinear motion of the proton. The F$-$$.$H$2$O spectrum shows evidence for Fermi interactions between several energy levels. Analysis of the spectra in the context of the potential surface probed by the shared proton is discussed.