MD simulations distinguish acetone and methanol effects on ice hydrogen bonding at 223 K

{"The Gezelter group modeled Yettapu, Manning, and Cyran’s 2023 SFG experiments by placing methanol or acetone monolayers on the basal face of a 6×6×6 Ice-Ih slab. They tracked QLL thickness via density profiles, computed instantaneous O-H stretch frequencies, and generated theoretical SFG spectra at both temperatures. No adsorbate-dependent difference in QLL growth appeared at either temperature, but the 223 K runs revealed clear divergence in hydrogen-bond statistics.","Acetone left a higher population of dangling OH groups whose secondary waters exhibited red-shifted stretches below 3100 cm⁻¹, producing a broader frequency distribution. Methanol formed additional donor-acceptor bonds, reducing that population and narrowing the distribution. The resulting local electric-field perturbation offers a plausible mechanism for the experimental SFG intensity drop at ~3170 cm⁻¹ observed only with acetone.","These results refine climatological parameterizations that treat all volatile organics as equivalent perturbers of the ice-vapor interface. Because the frequency shift arises from specific hydrogen-bond topology rather than bulk melting, models relying solely on QLL thickness may underestimate acetone’s influence on heterogeneous reaction rates and trace-gas uptake.","Next steps include direct comparison of the computed SFG tensors with new temperature-dependent spectra and extension to mixed adsorbate layers representative of Arctic boundary-layer conditions."}