Adsorption study of acetic acid on ice surfaces was performed by combining experimental and theoretical approaches. The experiments were conducted between 193 and 223 K using a coated wall flow tube coupled to a mass spectrometric detection. Under our experimental conditions, acetic acid was mainly dimerized in the gas phase. The surface coverage increases with decreasing temperature and with increasing concentrations of acetic acid dimers. The obtained experimental surface coverages were fitted according to the BET theory in order to determine the enthalpy of adsorption deltaH(ads) and the mololayer capacity N(M(dimers)) of the acetic acid dimers on ice: deltaH(ads) = (-33.5 +/- 4.2) kJ mol(-1), N(M(dimers)) = (l1.27 +/- 0.25) x 10(14) dimers cm(-2). The adsorption characteristics of acetic acid on an ideal ice I(n)(0001) surface were also studied by means of classical molecular dynamics simulations in the same temperature range. The monolayer capacity, the configurations of the molecules in their adsorption sites, and the corresponding adsorption energies have been determined for both acetic acid monomers and dimers, and compared to the corresponding data obtained from the experiments. In addition, the theoretical results show that the interaction with the ice surface could be strong enough to break the acetic acid dimers that exist in the gas phase and leads to the stabilization of acetic acid monomers on ice.

Adsorption studies of acetone and of 2,3-butanedione on ice surfaces were performed using a new vertical coated wall flow tube coupled to a mass spectrometric detection. Adsorption of acetone on ice was found to be totally reversible for ice temperatures ranging from 193 to 223 K and for gas phase acetone concentrations varying between 5.4 Â 10 10 and 6.4 Â 10 13 molecules cm À3 . Adsorption of 2,3-butanedione was also reversible at 213 and 223 K but partially irreversible at 193 and 203 K when its concentrations were larger than 1 Â 10 13 molecules cm À3 . It was shown that, at 203 K, the surface coverage increases when the ice surface contains large and dense cracks but is independent of the presence of cracks at 223 K. The surface coverage also increases with decreasing temperature and with increasing acetone or 2,3-butanedione concentrations. The obtained experimental surface coverages were fitted according to the Langmuir and BET theories in order to determine the enthalpy of adsorption DH ads and the monolayer capacity N M . The following values of N M were derived (in units of 10 14 molecule cm À2 ): N M ¼ 1.3 AE 0.2 for acetone and N M ¼ 1.2 AE 0.5 for 2,3-butanedione. The corresponding enthalpies of adsorption are (in kJ mol À1 ): À49 AE 7 for acetone and À59 AE 8 for 2,3-butanedione. The results are discussed and compared with previous determinations for acetone. Finally, the obtained results are used to estimate the partitioning of acetone between the ice and gas phases in clouds of the upper troposphere.

Adsorption study of ethanol on ice surfaces were performed by combining experimental and theoretical approaches. The experiments were conducted using a coated wall flow tube coupled to a mass spectrometric detection. The surface coverage increases with decreasing temperature and with increasing ethanol concentrations. The obtained experimental surface coverages were fitted according to the B.E.T. theory in order to determine the enthalpy of adsorption ∆H ads and the monolayer capacity N M : ∆H ads = -57 ± 8 kJ mol -1 , N M = (2.8 ± 0.8)×10 14 molecule cm -2 . The adsorption characteristics of ethanol on a proton disordered Ih(0001) ice surface were also jointly studied by performing classical molecular dynamics simulations. More specifically, the configurations of the molecules in their adsorption sites and the corresponding adsorption energies have been studied as a function of temperature and coverage. In the simulations, the saturation coverage is around N M = 3.2×10 14 molecule cm -2 , and corresponds to an adsorption energy equal to -56.6 kJ mol -1 , in good agreement with the experimental value. The results are discussed and compared with previous determinations for alcohols.