Absolute rate constants have been measured for the gas-phase reactions of hydroxyl radicals with a series of ketones: acetone (k 1 ), 2-butanone (k 2 ), 3-methyl 2-butanone (k 3 ), 4-methyl 2-pentanone (k 4 ), and 5-methyl 2-hexanone (k 5 ). Experiments were carried out using the pulsed laser photolysis-laser-induced fluorescence technique over the temperature range 243-372 K. The obtained kinetic data were used to derive the Arrhenius expressions: [(193 ( 65)/T]; k 4 ) (0.759 ( 0.126) × 10 -12 exp[(834 ( 46)/T], and k 5 ) (1.33 ( 0.63) × 10 -12 exp[(649 ( 140)/T] (in units of cm 3 molecule -1 s -1 ). At room temperature, the rate constants obtained (in units of 10 -12 cm 3 molecule -1 s -1 ) were as follows: acetone (0.184 ( 0.024); 2-butanone (1.19 ( 0.18); 3-methyl 2-butanone (2.87 ( 0.29); 4-methyl 2-pentanone (12.1 ( 0.9); and 5-methyl 2-hexanone (10.3 ( 1.0). Our results are compared with the previous determinations and discussed in terms of structure-reactivity relationships.

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.

Absolute rate constants have been measured for the gas phase reactions of hydroxyl radicals with a series of aliphatic acetates:  methyl acetate (k 1), ethyl acetate (k 2), n-propyl acetate (k 3), n-butyl acetate (k 4), and n-pentyl acetate (k 5). Experiments were carried out using the pulsed laser photolysislaser induced fluorescence technique over the temperature range 243−372 K. The obtained kinetic data were used to derive the Arrhenius expressions, and since the Arrhenius plots were slightly curved they were fitted, using a three-parameter expression. The Arrhenius expressions obtained are:  k 1 = (0.53 ± 0.09) × 10-12 exp[−(128 ± 102)/T] ; k 2 = (0.48 ± 0.09) × 10-12 exp[(397 ± 103)/T]; k 3 = (1.03 ± 0.12) × 10-12 exp[(370 ± 69)/T] ; k 4 = (2.10 ± 0.28) × 10-12 exp[(299 ± 81)/T], and k 5 = (2.75 ± 0.46) × 10-12 exp[(302 ± 102)/T] (in units of cm3 molecule-1 s-1). At room temperature, the rate constants obtained (in units of 10-12 cm3 molecule-1 s-1) were as follows:  methyl acetate, 0.32 ± 0.03; ethyl acetate, 1.67 ± 0.22; n-propyl acetate, 3.42 ± 0.26 ; n-butyl acetate, 5.52 ± 0.51; n-pentyl acetate, 7.34 ± 0.91. Our results are compared with the previous determinations and discussed in terms of structure−activity relationships.