The growth and characterization of sulfuric acid (H2S04) films in ultrahigh vacuum (UHV) is described. The films were synthesized in situ by co-condensing SO3 and H20 onto a single crystal metal surface at 100 K and carefully annealing the mixtures above 160 K. Films were typically 30-50 monolayers thick and were characterized using Fourier transform infrared reflection absorption spectroscopy (FTIRAS), temperatureprogrammed desorption (TPD), and X-ray photoelectron spectroscopy ( X P S ) . The FTIRAS, TPD, and XPS spectra show that solid homogeneous mixtures of varying water content can be prepared, from approximately 10 mol % H2S04 to nearly pure H2S04. The nearly pure films can be prepared in crystalline and amorphous forms, depending on the annealing procedure employed. Some surface chemical properties of the pure H2S04 films were investigated. 2-Propanol is readily adsorbed and absorbed by H2S04, with extensive dehydration to water and propene occurring at relatively low temperatures (<320 K). Pure solid HzSO4 does not adsorb or absorb HCl at 100 K, in contrast to ice, which readily adsorbs HCl at 100 K, but in striking similarity to concentrated, liquid H2S04 at room temperature.

The interactions of gas-phase acetone with liquid sulfuric acid solutions are described. The solutions were prepared as 0.05−0.10 μm thick films deposited on single-crystal metal substrates. Experiments were carried out over broad ranges of acid composition (70 − >96 wt % H2SO4), temperature (180−220 K), and acetone pressure (10-7−10-3 Pa). Two types of measurements are reported:  the time-dependent acetone uptake probability, and the infrared spectra of absorbed acetone and its reaction products. From the infrared measurements, a reaction scheme is identified in which gas-phase acetone is taken up by sulfuric acid to form protonated acetone. In solutions containing more than 70 wt % H2SO4, protonated acetone undergoes a self-condensation/dehydration reaction to form mesityl oxide. In films that contain 85 wt % or more H2SO4, a second reaction sequence occurs, ultimately resulting in the formation of trimethylbenzene. The uptake probability measurements are consistent with the infrared data. In 70 wt % H2SO4, the acetone uptake probability rapidly decreases from an initial value near unity to a steady-state value of zero, due to the formation of a saturated acetone + sulfuric acid solution. The Henry's law solubility constants of acetone in 70 wt % H2SO4 were obtained from the integrated uptake measurements. The temperature dependence of the measurements implies that the standard-state enthalpy and entropy changes of acetone solution in 70 wt % sulfuric acid are −66 kJ mol-1 and −249 J mol-1 K-1, respectively. In the more concentrated films, the steady-state uptake probability is never measured to be zero, since absorbed acetone goes on to form the condensation/dehydration products. A two-step kinetic scheme is proposed to account for the reactions of acetone in sulfuric acid. By fitting the data to the model predictions, the Henry's law solubility constants and the reaction rate constants may be estimated.

Abstract. A new heterogeneous reaction, namely the sulfate-Unfortunately, virtually all studies of H2SO4-catalyzed and mediated conversion of acetone to 4-methyl-3-penten-2-one and promoted reactions have been carried out under conditions far trimethylbenzene, is reported. The reaction products were observed in their absorbed states by Fourier transform infrared spectroscopy and in the gas phase by mass spectrometry. In addition, protonated, absorbed acetone was observed under certain conditions. The reaction exhibits a strong concentration and / or temperature dependence, with non-reactive uptake as protonated acetone dominating at low temperatures and sulfate concentrations and reactive uptake occurring above 200 K and 75 wt. % H2SO 4. Under conditions where reactive uptake occurs, the steady-state acetone loss probability is roughly 40%.removed from those in the upper troposphere: at room temperature, in concentrated (>96 wt. %) solution, and not via accommodation of the reactants from the gas phase.In this work, we present initial results of a study of the interaction of one tropospherically abundant compound, acetone [(CH3)2CO], with sulfate. The experiments were carried out on ultrathin sulfate films (--100 monolayers thick) of composition between 60 and 96 wt. % H2SO 4 and at temperatures between 180 and 250 K. Infrared spectroscopy and mass spectrometry were used to identify the absorbed and gas-phase reaction It was not possible in this study to assess the relative effects of products, respectively. temperature and concentration on the reactivity of sulfate toward acetone.