Field-Induced Heterolytic Dissociation of Isolated HF and HCl

Abstract The influence of static electric fields on the electronic structure and dissociation behavior of the polar diatomics HF and HCl is investigated using quantum chemical calculations. Ground- and excited-state potential energy surfaces (PESs) are computed as a function of bond distance and external electric field strength to examine field-induced modifications of chemical bonding. The calculations reveal pronounced bond softening and progressive destabilization of both molecules with increasing field intensity. Notably, the ground-state PES of HCl becomes entirely dissociative at field strengths of approximately 500 MV/cm, whereas HF requires a substantially stronger field of nearly 720 MV/cm to induce dissociation. This difference reflects the greater polarizability and weaker bond localization in HCl relative to HF, providing a molecular-scale perspective on the contrasting macroscale acid strengths of the two species. Field-dependent dipole moments further demonstrate the stronger electronic response of HCl to external perturbations, highlighting how molecular polarizability drives electric-field-induced bond activation. Ultimately, these results map out a detailed picture of field-controlled dissociation in hydrogen halides, supporting the view that local electric fields generated by surrounding hydrogen-bonding networks play a key role in modulating bond activation and condensed-phase acidity.