The application of transition state theory to gas–surface reactions in Langmuir systems

Abstract

Quantum state-resolved gas/surface reaction dynamics probed by reflection absorption infrared spectroscopy Rev. Sci. Instrum. 84, 053902 (2013) Transition state theory ͑TST͒ has long been applied to gas-surface reactions for the purpose of characterizing and predicting desorption rate coefficients, but current perceptions of its use exclude TST from meaningful description of the sticking coefficient for partially covered surfaces. This paper re-examines the application of TST to partially covered surfaces, and in particular to Langmuir systems with barrierless adsorption. An analogy is drawn in the present work between barrierless adsorption processes and gas-phase radical-radical recombination reactions that reveals a simple method by which TST can describe kinetics in Langmuir systems. Construction of a model ''hard-wall'' Hamiltonian that reflects the exclusion of adsorbates from occupied sites enables the kinetics in Langmuir systems to be described by constructing a transition state surface that does not permit adsorption at occupied sites. This method gives analytic expressions for the TST sticking coefficient ͑and desorption rate coefficient͒ in two important limiting cases for the gas-surface dynamics, and resolves previous difficulties in the TST description of Langmuir systems.

Current Status of Transition-State Theory

“…In related work, Anton attempted to include adsorbate coverage dependence in classical TST and tested the method for desorption reactions. Pitt et al argue that this derivation cannot be correct for barrierless adsorption. In a more empirical approach, the desorption of CO from metals has been modeled using harmonic RRKM theory in which the vibrational frequencies of the reactants and transition state were taken from experimental data …”

“…Desorption from Surfaces . The recent body of work from Pitt et al − provides an excellent discussion of the applicability of TST to thermal surface adsorption in the absence of an intrinsic barrier as well as a review of the relevant literature. They argue that the variationally optimized dividing surface need not necessarily be located at infinite separation from the surface as had been previously suggested in the literature.…”

Ozone Interaction with Polycyclic Aromatic Hydrocarbons and Soot in Atmospheric Processes: Theoretical Density Functional Study by Molecular and Periodic Methodologies

“…The following analysis of the chemisorption process makes use of the kinetical analysis of the reaction, as described above. We estimate the sticking coefficient γ theor by transition state theory (TST) following methods described by Pitt, Gilbert, and Ryan 38 and by Chorkendorff and Niemantsverdriet. 39 Thus, we adopt a Langmuir model, which is based on the following assumptions: (i) there are no interadsorbate interactions, (ii) the adsorbates are localized in equivalent sites on a homogeneous surface, (iii) the occupation of a site excludes further adsorption in that site, and (iv) only a monolayer adsorption is possible.…”

On the Potential of Gallium- and Indium-Based Liquid Metal Membranes for Hydrogen Separation

“…The information available does not allow for every pre-exponential factor to be calculated directly via Equations ( 10) and (11). Hence, Equation ( 12) is applied for the dissociative adsorption and Hess' law is employed to enable the use of relative entropies, the resulting expressions being Equations ( 13)-( 18) [20,27]. The pre-exponential factor for diffusion constitutes parameters related to the diffusive jump distance and unit cell geometry (a and γ D ), these are added to relate the rate of diffusion to the jumping frequency [28].…”

“…The Sackur-Tetrode equation requires the molecular volume in the gas phase (which is determined via the ideal gas law) and the thermal wavelength, as shown in Equations ( 25) and (26), respectively. For the determination of the entropy contribution of one translational degree of freedom, argon is used as a reference, as shown in Equation (27). The molar mass of this noble gas is 39.95 g mol −1 and its reference entropy has a value of 154.6 J mol −1 K −1 [45,46].…”