Sticking Coefficient¶

The conditional fraction or probability of incident adsorptive particles that become adsorbed on a specified surface, linking arrival flux to adsorption rate under declared particle, surface, energy, coverage, temperature, and observation-time conditions.

Version: v1 · 2026-08-30 · History
Domain-specific #: 2856
Origin domain: surface chemistry
Subdomain: adsorption kinetics
Aliases: Sticking probability, Adsorption sticking coefficient

Core Idea¶

The Sticking Coefficient is the ratio of the adsorption rate to the rate at which an adsorptive strikes the total surface, including covered and uncovered portions. Equivalently, under an event-counting experiment it is the conditional probability that an incident atom or molecule becomes adsorbed according to a declared residence or binding criterion. Its usual range is zero to one: zero means no counted impacts lead to adsorption, and one means every counted impact does.^[1]

The coefficient is not an intrinsic constant of a chemical species or surface name alone. It depends on incident translational, rotational, and vibrational energy; angle; surface temperature; coverage; surface structure and defects; adsorbate state; competing species; and the timescale and criterion used to distinguish trapping, migration, adsorption, and desorption. The initial sticking coefficient S₀ refers to a clean or zero-coverage surface under specified conditions. Coverage-dependent coefficients describe how site occupation and adsorbate interactions change capture as adsorption proceeds.

The locked identity is: declared incident particle flux at a specified surface + operational adsorption event within a stated observation window -> adsorbed-event rate divided by incident-event rate, conditioned on energy, angle, temperature, coverage, and surface state. It is a kinetic interface quantity: adsorption is the underlying process; the sticking coefficient measures the capture efficiency of encounters.

Structural Signature¶

the adsorptive — gas-phase or solution-phase atom, molecule, radical, cluster, or solute approaching a surface;
the adsorbent surface — material, crystallographic face, morphology, cleanliness, defect structure, and preparation;
the incident ensemble — flux or encounter population with specified energy and angular distributions;
the denominator — number or rate of particles striking the defined total surface;
the adsorption criterion — binding, thermal accommodation, residence time, state transition, or other rule distinguishing “stuck” from scattered;
the numerator — incident particles satisfying that adsorption criterion;
the coefficient S — numerator divided by denominator, usually between zero and one;
surface coverage θ — occupied fraction or adsorbate population that changes available sites and interactions;
initial coefficient S₀ — limiting or measured value for a clean, nominally unoccupied surface;
competing pathways — prompt reflection, transient trapping, surface migration, reaction, and desorption;
state dependence — temperature, energy, angle, structure, and composition must accompany a reported number;
measurement or simulation protocol — beam uptake, pressure change, spectroscopy, molecular trajectories, or other method establishes events.

A reported value without denominator, adsorption criterion, and physical conditions is incomplete.

What It Is Not¶

Not adsorption capacity. Capacity is how much a surface can hold; sticking is the fraction of current encounters captured.
Not surface coverage. Coverage is the occupied state resulting from adsorption and desorption; it is also an input influencing S.
Not an adsorption isotherm. An isotherm relates equilibrium uptake to pressure or concentration at fixed temperature; sticking is kinetic.
Not the adsorption rate itself. Rate equals incident flux times an appropriate sticking coefficient, subject to definitions and transport effects.
Not binding energy. Stronger binding can affect sticking and residence but does not determine it alone because entrance barriers and energy transfer matter.
Not residence time. A particle can initially stick yet desorb rapidly; the event criterion decides whether that trajectory counts.
Not accommodation coefficient generally. Energy accommodation measures exchange of kinetic or thermal energy and need not imply adsorption.
Not a universal material constant. Surface history, coverage, and incident state can change it markedly.
Not ordinary friction or adhesion. The term describes microscopic adsorption events at an interface.

Scope of Application¶

Sticking coefficients are used in surface chemistry and physics, heterogeneous catalysis, thin-film deposition, epitaxy, semiconductor processing, vacuum science, plasma–surface interactions, atmospheric and interstellar grain chemistry, and reaction-dynamics experiments. They connect a supplied flux to the number of species that enter an adsorbed population and therefore constrain reaction and growth rates.

Gas–solid experiments commonly use molecular beams, dosing, pressure uptake, mass spectrometry, or spectroscopic coverage measurements. The incident flux must be calibrated and corrections may be needed for pumping, desorption, and nonuniform exposure. Molecular dynamics classifies trajectories as reflected, transiently trapped, or adsorbed under a time criterion.

The concept has been extended to liquid–solid adsorption by defining encounters through solute density, diffusion, residence layers, or random-walk arrival rates rather than gas pressure and ballistic flux. Zhang, Savara, and Getman demonstrate a molecular-dynamics method extracting a liquid–solid sticking coefficient and macroscopic adsorption rate for methanol at Pt(111) in water.^[2] That extension preserves the ratio/probability role but changes the denominator's operational construction.

Clarity¶

The IUPAC definition uses total surface in the impact denominator, not only empty sites.^[1] Therefore coverage dependence belongs in the coefficient. A Langmuir-style ideal model may approximate S(θ)=S₀(1-θ) when identical sites fill independently and occupied sites cannot accept more particles. Real systems can deviate through precursor migration, dissociative adsorption requiring multiple sites, attractive or repulsive adsorbate interactions, reconstruction, island formation, and activated entrance barriers.

“Sticking probability” is a common near-synonym when the experiment follows individual encounters. “Coefficient” emphasizes the flux ratio used in kinetics. Both require a time horizon: counting any transient residence as sticking yields a different value from requiring survival for a specified duration or conversion into a chemisorbed state.

Manages Complexity¶

Surface reaction rates depend on a cascade: transport to the interface, collision, energy transfer, trapping, migration, reaction, and desorption. The sticking coefficient compresses the entrance portion into one conditional factor. Given incident flux J, an idealized uptake rate per area is S J, after aligning definitions and accounting for site or stoichiometric factors.

The coefficient also exposes where a rate model is sensitive. A low reaction yield can reflect low arrival flux, low sticking, short residence, or slow surface reaction. Measuring S separates capture from downstream chemistry. Coverage-resolved measurements reveal poisoning, site blocking, cooperative adsorption, or surface reconstruction without treating all loss as one rate constant.

Abstract Reasoning¶

If incident flux doubles while conditions and S remain fixed, initial adsorption rate doubles.
If coverage blocks independent equivalent sites, S tends to decrease with θ; nonmonotonic behavior signals additional mechanisms.
Increasing surface temperature can lower sticking by shortening trapping time, but activated adsorption can produce more complex trends.
A particle can exchange energy and scatter, so accommodation does not entail sticking.
An observed uptake rate cannot yield S until transport limitations and desorption during measurement are separated.
Comparing surfaces requires matched incident energy, angular distributions, cleanliness, coverage, and event criteria.
Liquid-phase extension requires a denominator based on encounter rate or solute density, not direct reuse of gas impingement pressure formulas.
Values above one indicate inconsistent counting, dissociation/stoichiometry conventions, or secondary processes requiring explicit redefinition.

Knowledge Transfer¶

The abstraction transfers exactly from catalysis to deposition, plasma processing, astrochemistry, and surface reaction dynamics because incident ensemble, interface, capture criterion, and flux ratio persist. Gas–solid and liquid–solid cases are variants whose arrival processes differ.

The broader residue belongs to Conditional Probability, Rate, Encounter Surface, Capture, and Efficiency. Social “stickiness” or customer retention is metaphorical and should not be routed here.

Examples¶

Clean-surface molecular beam: counted adsorbed molecules divided by calibrated beam impacts estimates S₀ at a declared energy and temperature.
Coverage blocking: as adsorbates occupy sites, fewer new impacts adsorb and S(θ) declines.
Activated dissociation: a diatomic molecule's sticking increases with incident energy when a dissociation barrier is crossed.
Precursor migration: a weakly trapped particle samples several sites before adsorption, so sticking can exceed the instantaneous empty-site fraction.
Thin-film growth: incoming precursor flux times sticking constrains incorporation and thickness rate.
Liquid–solid simulation: trajectory residence statistics near Pt(111) yield a sticking coefficient for methanol from aqueous solution.
Astrochemical grain: cold surface temperature can make incident gas species more likely to remain on an ice grain.

Structural Tensions¶

Simple ratio vs. complex trajectory. One number summarizes reflection, trapping, migration, reaction, and desorption choices.
Intrinsic interaction vs. operational criterion. Physical dynamics are real while classification depends on observation time and detection.
Clean-surface benchmark vs. working surface. S₀ aids comparison but catalysts operate under coverage and reconstruction.
Ballistic gas arrival vs. diffusive liquid encounter. The role transfers while denominator construction changes.
Local heterogeneity vs. averaged coefficient. Defects and facets differ, yet experiments often report one area average.
Kinetic capture vs. equilibrium uptake. High sticking can coexist with low equilibrium coverage if desorption is rapid.

Structural–Framed Character¶

Sticking Coefficient is structural. Conditional event counts and physical state define the value. Operational choices matter at the measurement boundary, but the abstraction is a quantitative physical relation rather than an institutional judgment.

Structural Core vs. Domain Accent¶

The core is successful transitions divided by opportunities under specified conditions. The domain accent is adsorptive flux, material surface, adsorption, coverage, scattering, residence, and surface temperature. This distinguishes the node from general Probability or Rate.

Conditional Probability — capture is conditioned on an incident encounter and state.
Rate — the coefficient links incident and adsorption fluxes.
Encounter Surface — the boundary is where alternatives branch.
Selection — only some incident trajectories enter the adsorbed state.
Efficiency — successful captures are normalized by supplied opportunities.
State Dependence — coverage and temperature alter the relation.

The prospective DAG uses composition under existing domain_specific:adsorption, the process whose kinetic capture fraction is measured.

Relationships to Other Abstractions¶

Current abstraction Sticking Coefficient Domain-specific

Parents (1) — more general patterns this builds on

Sticking Coefficient is part of Adsorption Domain-specific

coverage and temperature alter the relation.

Hierarchy paths (2) — routes to 2 parentless roots

Sticking Coefficient → Adsorption → Interface → Boundary

Show alternative path (1)

Neighborhood in Abstraction Space¶

Sticking Coefficient sits in a sparse region of the domain-specific corpus (98^th percentile for distinctiveness): few abstractions share its structure, so a faithful description tends to retrieve it precisely.

Family — Unclustered & Miscellaneous (1565 abstractions)

Nearest neighbors

Computed from structural-signature embeddings · 2026-09-08

Not to Be Confused With¶

adsorption rate;
adsorption capacity;
surface coverage;
adsorption isotherm;
binding or activation energy;
residence time;
accommodation coefficient;
macroscopic adhesion or friction;
a constant independent of experimental conditions.

References¶

[1] IUPAC, “Sticking coefficient,” Compendium of Chemical Terminology, https://doi.org/10.1351/goldbook.S06012. registry ↩a ↩b

[2] Xiaohong Zhang, Aditya Savara, and Rachel B. Getman, “A Method for Obtaining Liquid–Solid Adsorption Rates from Molecular Dynamics Simulations: Applied to Methanol on Pt(111) in H2O,” Journal of Chemical Theory and Computation 16(4), 2020, 2680–2691, https://doi.org/10.1021/acs.jctc.9b01249. registry ↩

[3] “Sticking coefficient,” Wikipedia, frozen revision 1284764526 (2025-04-09), https://en.wikipedia.org/wiki/Sticking_coefficient. registry