Adsorption of Benzaldehyde at the Surface of Ice, Studied by Experimental Method and Computer Simulation

Abstract

Adsorption study of benzaldehyde on ice surfaces is performed by combining experimental and theoretical approaches. The experiments are conducted over the temperature range 233-253 K using a coated wall flow tube coupled to a mass spectrometric detector. Besides the experimental way, the adsorption isotherm is also determined by performing a set of grand canonical Monte Carlo simulations at 233 K. The experimental and calculated adsorption isotherms show a very good agreement within the corresponding errors. Besides, both experimental and theoretical studies permit us to derive the enthalpy of adsorption of benzaldehyde on ice surfaces DeltaH(ads), which are in excellent agreement: DeltaH(ads) = -61.4 +/- 9.7 kJ/mol (experimental) and DeltaH(ads) = -59.4 +/- 5.1 kJ/mol (simulation). The obtained results indicate a much stronger ability of benzaldehyde of being adsorbed at the surface of ice than that of small aliphatic aldehydes, such as formaldehyde or acetaldehyde. At low surface coverages the adsorbed molecules exclusively lie parallel with the ice surface. With increasing surface coverage, however, the increasing competition of the adsorbed molecules for the surface area to be occupied leads to the appearance of two different perpendicular orientations relative to the surface. In the first orientation, the benzaldehyde molecule turns its aldehyde group toward the ice phase, and, similarly to the molecules in the lying orientation, forms a hydrogen bond with a surface water molecule. In the other perpendicular orientation the aldehyde group turns to the vapor phase, and its O atom interacts with the delocalized pi system of the benzene ring of a nearby lying benzaldehyde molecule of the second molecular layer. In accordance with this observed scenario, the saturated adsorption layer, being stable in a roughly 1 kJ/mol broad range of chemical potentials, contains, besides the first molecular layer, also traces of the second molecular layer of adsorbed benzaldehyde.

Adsorption of Methylene Fluoride and Methylene Chloride at the Surface of Ice under Tropospheric Conditions: A Grand Canonical Monte Carlo Simulation Study

“…Indeed, the GCMC method has been successfully applied to calculate the adsorption isotherms of water and other small molecules at various different solid surfaces, such as at carbonaceous materials, 15-23 self-assembled monolayers, 24,25 covalent organic frameworks, [26][27][28] protein crystals, 29 metal oxides, [30][31][32][33] zeolites, [34][35][36][37][38][39][40][41] kaolinite, [42][43][44] and ice. [45][46][47][48][49][50][51][52][53] Further, besides the adsorption isotherms themselves, the structure and energetics of the adsorption layer can also be analyzed in detail in such simulations. However, we are not aware of any simulation or other theoretical studies (e.g., ab initio calculations) of the adsorption of halogenocarbon molecules at the surface of ice.…”

Adsorption of H2O2 at the surface of Ih ice, as seen from grand canonical Monte Carlo simulations

“…In recent years, many experimental and theoretical studies have been devoted to a thorough characterization of the interaction between the surface of ice and a wide variety of atmospheric trace gases [4][5][6][7][8][9][10][11][12][13][14]. Among the information recorded in these works, full adsorption isotherm appears much useful because it gives directly the surface coverage as a function of temperature and partial pressure.…”

“…Thus, by systematically varying the adsorbate chemical potential in a set of simulations the adsorption isotherm, i.e., the number of adsorbed molecules per surface unit as a function of the chemical potential, can be calculated. The GCMC method has successfully been applied to calculate the adsorption isotherm in a wide variety of such systems [6][7][8][9]13,14,[17][18][19][20][21][22][23][24][25], including trace gases on ice [6][7][8][9]13,14].…”

Molecular Dynamics Simulation of the Adsorption of Oxalic Acid on an Ice Surface

“…During the last decade, a growing number of experimental [9][10][11][12][13][14][15][16][17][18] and theoretical [19][20][21][22][23][24][25][26][27][28][29][30][31][32] studies have thus been devoted to the characterization of the interactions between small organic molecules and ice. More specifically, coated wall flow tube and Knudsen cell experiments have been performed to characterize the uptake of different partially oxidized hydrocarbon molecules (POHs), including aldehydes and alcohols, [12] carboxylic acids, [10,16,18,23] and ketones, [11,14,15,17] by ice.…”

“…[24] Monte Carlo simulations coupled to the cavity insertion widom (CIW) method [35] have been devoted to the comparison of the solvation free energy of various molecules, including POHs (such as methanol, formaldehyde, formic acid, and acetone) across the ice/vapor interface. [27] A series of GCMC studies has also been performed to simulate the adsorption isotherms of methanol, [25] formaldehyde, [28] formic acid, [29] acetone, [30] and benzaldehyde [32] molecules on ice at tropospheric conditions. The simulated isotherms showed a remarkable agreement with available experimental measurements, [25,29,32] demonstrating that classical simulations are accurate and useful tools for studying interactions between POHs and ice at tropospheric temperatures.…”