Electric Field Effect on Condensed-Phase Molecular Systems. IX. Control of Proton Displacement in Matrix-Isolated Hydrogen Chloride–Water Complexes

This article focuses on the manipulation of molecular bond lengths by an external electric field. A uniform dc electric field with strength up to 1.5 × 10⁸ V/m was applied to HCl–H₂O and HCl–D₂O complexes isolated in solid Ar matrices by using the ice film nanocapacitor method. The field-dependent vibrational spectra of the samples showed an extraordinarily large Stark shift of the proton vibration (H–Cl stretch) frequency of the HCl–water complexes in the electric field compared to that of the isolated HCl molecules. The results indicated that the applied electric field reversibly changed the equilibrium position of the acidic proton along the proton-transfer coordinate of the complexes. The proton displacement was highly asymmetric with respect to the elongation and contraction of the H–Cl bond and changed the vibrational coupling behavior between the proton motion and the normal mode of the hydrating D₂O molecule.