Interaction of methanol, acetone and formaldehyde with ice surfaces between 198 and 223 K

Abstract

The rate and extent of physical adsorption of methanol, acetone and formaldehyde on ice were measured as a function of concentration and temperature. The gas–ice interaction was analysed by applying adsorption isotherms to determine temperature dependent Langmuir constants, K(T) and saturation surface coverage, N_max. At low coverage a partitioning constant K^#(T) was derived. The dependence of K^# on temperature is given by K^#(T) = 6.24 × 10⁻¹² exp(6178/T) cm for methanol and K^#(T) = 1.25 × 10⁻¹⁰ exp(5575/T) cm for acetone. For formaldehyde a temperature independent expression, K^# = 0.7 cm was derived. From these data adsorption enthalpies ΔH_ads of (−46 ± 7) and (−51 ± 10) kJ mol⁻¹ were obtained for acetone and methanol, respectively. The results were used to calculate the equilibrium partitioning of these trace gases to ice surfaces under conditions relevant to the atmosphere.