Interactions of N₂O₅ and Related Nitrogen Oxides with Ice Surfaces: Desorption Kinetics and Collision Dynamics

Abstract

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.

Production of Br2from N2O5and Br–in Salty and Surfactant-Coated Water Microjets

“…For 100 kJ mol –1 collisions of N 2 O 5 with 8 m LiBr/H 2 O at 240 K, Figure reveals that energy dissipation into surface and subsurface H 2 O must be rapid in order for the N 2 O 5 thermal desorption (TD) signal to be so strong . Parallel behavior is observed for collisions of N 2 O 5 with the surface of ice, where thermalization is also extensive . Recent experiments by Langlois et al further suggest that impinging N 2 O 5 molecules that do not thermalize at the surface of water almost always scatter back into the gas phase: the probability for direct embedding of a molecule at 100 kJ mol –1 with the mass of N 2 O 5 below the interfacial region of amorphous ice is only 0.1% .…”

“…The reactive uptake probability P uptake (also called the uptake coefficient γ) is then equal to 1 – P escape . We use low translational energy, 10 kJ mol –1 (5 RT liq ) N 2 O 5 molecules in order to ensure that nearly all impinging N 2 O 5 molecules thermally equilibrate at the surface upon collision, a likely prerequisite for the reaction (as discussed later). − …”

“…34 Parallel behavior is observed for collisions of N 2 O 5 with the surface of ice, where thermalization is also extensive. 59 Recent experiments by Langlois et al further suggest that impinging N 2 O 5 molecules that do not thermalize at the surface of water almost always scatter back into the gas phase: the probability for direct embedding of a molecule at 100 kJ mol −1 with the mass of N 2 O 5 below the interfacial region of amorphous ice is only 0.1%. 69 On the basis of these studies, we were motivated to use a high-energy and high-flux beam to observe reactions of N 2 O 5 adsorbed on the surface of the LiBr/H 2 O microjet.…”

Interactions between the atmosphere, cryosphere, and ecosystems at northern high latitudes

“…Idealized molecular beam and light-scattering experiments have focused on building a fundamental understanding of how critical-scale ice clusters initially form and grow vis à vis vapour deposition on well-characterized surfaces (Kong et al, 2012;Thomson et al, 2015). Observations demonstrate that surfactants play an important role due to their ability to enhance and/or suppress the adsorption and desorption kinetics of atmospheric particles (Kong et al, 2014a;Papagiannakopoulos et al, 2014;Lejonthun et al, 2014;Thomson et al, 2013;Johansson et al, 2017). In particular, organic hydrocarbon surfactant layers -that for experimental purposes are used to model atmospherically relevant organic layers -have size-and temperature-dependent effects on ice nucleation, growth morphology, and molecular water uptake (Kong et al, 2014b;).…”

Interactions between the atmosphere, cryosphere and ecosystems at northern high latitudes

“…Idealized molecular beam and light scattering experiments have focused on building a fundamental understanding of 10 how critical scale ice clusters initially form and grow vis-à-vis vapor deposition on well-characterized surfaces (Kong et al 2012, Thomson et al 2015. Observations demonstrate that surfactants play an important role due to their ability to enhance and/or suppress the adsorption and desorption kinetics of atmospheric particles (Kong et al 2014a, Papagiannakopoulos et al 2014, Lejonthun et al 2014, Johansson et al 2017. In particular organic hydrocarbon surfactant layers -that for experimental purposes are used to model atmospherically relevant 15 organic layers -have size and temperature dependent effects on ice nucleation, growth morphology and molecular water uptake (Kong et al 2014b).…”