Surface Transformations and Water Uptake on Liquid and Solid Butanol near the Melting Temperature

Abstract

Water interactions with organic surfaces are of central importance in biological systems and many Earth system processes. Here we describe experimental studies of water collisions and uptake kinetics on liquid and solid butanol from 160 to 200 K. Hyperthermal D 2 O molecules (0.32 eV) undergo efficient trapping on both solid and liquid butanol, and only a minor fraction scatters inelastically after an 80% loss of kinetic energy to surface modes. Trapped molecules either desorb within a few ms, or are taken up by the butanol phase during longer times. The water uptake and surface residence time increase with temperature above 180 K indicating melting of the butanol surface 4.5 K below the bulk melting temperature. Water uptake changes gradually across the melting point and trapped molecules are rapidly lost by diffusion into the liquid above 190 K. This indicates that liquid butanol maintains a surface phase with limited water permeability up to 5.5 K above the melting point. These surface observations are indicative of an incremental change from solid to liquid butanol over a range of 10 K straddling the bulk melting temperature, in contrast to the behavior of bulk butanol and previously studied materials.

Water Accommodation on Ice and Organic Surfaces: Insights from Environmental Molecular Beam Experiments

“…69−71 The surface of BuOH is not expected to form a solid crystalline bilayer, but the observed resistance to water uptake may be associated with a related ordering of the surface layer. 35 The intriguing results confirm the importance of liquidlike properties in the surface layer for accommodation of water, as also suggested by the MeOH/graphite data.…”

“…35 BuOH has a melting point of 184.5 K, 67,68 and water interactions with both solid and liquid BuOH have been studied with the EMB method. 35 Figure 8 shows calculated α obs values as a function of temperature based on TD probability data reported in Papagiannakopoulos et al 35 Below 180 K, the accommodation coefficient decreases with increasing temperature in a manner qualitatively similar to bulk accommodation on bare ice. 4 Above 180 K, α obs rapidly increases as the temperature approaches and crosses the melting point.…”

Oxidation of a model alkane aerosol by OH radical: the emergent nature of reactive uptake

“…Therefore, we consider recent literature. Measurements of water adsorbed on butanol through the butanol melting point 66 revealed an abrupt increase in water uptake as butanol liquefied. The authors were using water as a probe of the formation of liquid butanol a few degrees below the melting temperature, and elegantly demonstrated its presence.…”

Interactions of N2O5 and Related Nitrogen Oxides with Ice Surfaces: Desorption Kinetics and Collision Dynamics

“…Thus, the present study confirms previous observations of efficient energy transfer and gas trapping on ice 15,16 and other surfaces of environmental relevance. 20,33,34 NO and NO 2 rapidly desorb from pure ice with residence times that are too short to be resolved in the current experimental system. From experimental constraints, upper bounds for the surface binding energies of 0.16 ± 0.02 and 0.26 ± 0.03 eV are determined for NO and NO 2 , respectively.…”