Reevaluating Anomalous Electric Fields at the Air–Water Interface: A Surface-Specific Spectroscopic Survey

The notion that large electric fields at the air-water interface catalyze spontaneous chemical reactions has sparked significant debate, with far reaching implications for atmospheric chemistry and interfacial reactivity. Using vibrational sum frequency generation (SFG) spectroscopy, we test this hypothesis within the framework of this surface-specific method, comparing local electric field strengths at the air-water interface and in bulk water. By applying established vibrational frequency-to-field mappings to the OH stretch of interfacial and bulk water, we extract effective electric field distributions under ambient conditions. Contrary to prevailing claims, our SFG results reveal no spectroscopic evidence within this method for exceptionally strong or long-lived interfacial electric fields. Instead, bulk water consistently exhibits broader field distributions. The absence of key spectral signatures, such as red-shifted continua, or slowed spectral diffusion, further undermines the idea of anomalous surface fields. Our findings suggest that exceptionally large, long-lived interfacial fields are unlikely. This calls into question interpretations that attribute droplet chemistry primarily to such electric fields.