The detailed interactions of nitrogen oxides with ice are of fundamental interest and relevance for chemistry in cold regions of the atmosphere. Here, the interactions of NO, NO2, N2O4, and N2O5 with ice surfaces at temperatures between 93 and 180 K are investigated with molecular beam techniques. Surface collisions are observed to result in efficient transfer of kinetic energy and trapping of molecules on the ice surfaces. NO and NO2 rapidly desorb from pure ice with upper bounds for the surface binding energies of 0.16 ± 0.02 and 0.26 ± 0.03 eV, respectively. Above 150 K, N2O4 desorption follows first-order kinetics and is well described by the Arrhenius parameters Ea = 0.39 ± 0.04 eV and A = 10((15.4±1.2)) s(-1), while a stable N2O4 adlayer is formed at lower temperatures. A fraction of incoming N2O5 reacts to form HNO3 on the ice surface. The N2O5 desorption rates are substantially lower on pure water ice (Arrhenius parameters: Ea = 0.36 ± 0.02 eV; A = 10((15.3±0.7)) s(-1)) than on HNO3-covered ice (Ea = 0.24 ± 0.02 eV; A = 10((11.5±0.7)) s(-1)). The N2O5 desorption kinetics also sensitively depend on the sub-monolayer coverage of HNO3, with a minimum in N2O5 desorption rate at a low but finite coverage of HNO3. The studies show that none of the systems with resolvable desorption kinetics undergo ordinary desorption from ice, and instead desorption likely involves two or more surface states, with additional complexity added by coadsorbed molecules.

The kinetics of chlorine interactions with ice at temperatures between 103 and 165 K have been studied using molecular beam techniques. The Cl(2) trapping probability is found to be unity at thermal incident energies, and trapping is followed by rapid desorption. The residence time on the surface is less than 25 microg at temperatures above 135 K and approaches 1 s around 100 K. Rate constants for desorption are determined for temperatures below 135 K. The desorption kinetics follow the Arrhenius equation, and activation energies of 0.24 +/- 0.03 and 0.31 +/- 0.01 eV, with corresponding preexponential factors of 10(12.08+/-1.19) and 10(16.52+/-0.38) s(-1), are determined. At least two different Cl(2) binding sites are concluded to exist on the ice surface. The observed activation energies are likely to be the Cl(2)-ice binding energies for these states, and the Cl(2)-surface interactions are concluded to be stronger than earlier theoretical estimates. The surface coverage of Cl(2) on ice under stratospheric conditions is estimated to be negligible, in agreement with earlier work.

The formation of adsorbed layers of dinitrogen pentoxide, nitric acid, and water on graphite has been studied by molecular beam and light-scattering techniques. The desorption kinetics of N2O5 on graphite were described by the Arrhenius equation with an activation energy of 0.24 ± 0.03 eV and a pre-exponential factor of 2.3 × 10(10 ± 0.73) s−1, and N2O5 is concluded to bind more strongly than H2O to the graphite surface. Elastic helium scattering and light scattering were used to probe the formation of adlayers on the surface. Adsorption of pure N2O5 resulted in formation of thin adlayers at temperatures below 160 K. In coadsorption experiments N2O5 was concluded to facilitate the formation of thick N2O5−H2O ice layers at 155 K. In a similar way coadsorption of HNO3 and H2O resulted in the formation of thick adlayers at 170 K. N2O5 and HNO3 both bind more strongly than water to the graphite surface and are concluded to facilitate nucleation and growth of ice.