Adsorption, desorption, and surface diffusion kinetics of NH3 on MgO(100)

Arthur, David; Meixner, D. Laurence; Boudart, M.; George, Steven M.

doi:10.1063/1.461281

Cited by 53 publications

(45 citation statements)

References 50 publications

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“…The resultant CO 2 laser beam had a Gaussian spatial distribution, a pulse duration of ∼100 ns (fwhm), and an energy of ∼70 mJ/pulse. 31 The CO 2 laser beam was focused onto the Al 2 O 3 (0001) surface at 45°relative to the surface normal using an f ) 75 cm focal length ZnSe lens. The focused laser beam illuminated an elliptical area approximately 0.75 mm × 1.1 mm on the Al 2 O 3 surface.…”

Section: Laser-induced Thermal Desorption (Litd)mentioning

confidence: 99%

Surface Sensitive Studies of the Reactive Uptake of Chlorine Nitrate on Ice

1997

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The reactive uptake of chlorine nitrate (ClONO 2 ) on ice surfaces (ClONO 2 + H 2 O f HOCl + HNO 3 ) was studied with surface sensitivity using laser-induced thermal desorption (LITD) techniques. Thin films of vapor-deposited ice were exposed to ClONO 2 vapor at substrate temperatures from 75 to 140 K. The reactive uptake of ClONO 2 was directly measured by monitoring the hydrolysis reaction products, HOCl and HNO 3 , on the ice surface in real time. At low temperatures from 75 to 110 K, the HOCl coverage initially increased rapidly with ClONO 2 exposure, indicating an efficient hydrolysis reaction. After longer ClONO 2 exposures, the rate of HOCl production decreased and the HOCl reached a constant coverage. A reaction probability of γ ) 0.03 was calculated for the reactive uptake of ClONO 2 on ice and was independent of temperature from 75 to 110 K. At temperatures greater than 110 K, the reaction probability decreased with increasing temperature and reached a value of γ ) 0.005 at 140 K. This decrease in the reaction probability with increasing substrate temperature is consistent with a precursor-mediated adsorption model. The good fits to the precursor-mediated adsorption model indicate that the ClONO 2 hydrolysis reaction has a low activation barrier. The precursormediated adsorption model extrapolated to stratospheric temperatures predicts a reaction probability that is significantly lower than the accepted literature value of γ ∼ 0.3. This discrepancy may be caused by the higher pressures and the dynamic ice surface at stratospheric conditions that could enhance the reaction probability. The constant HOCl coverage reached after longer ClONO 2 exposures is attributed to the poisoning of the ice surface by product HNO 3 . Calibrated HNO 3 signals at 86 and 140 K revealed that the ClONO 2 hydrolysis reaction is inhibited at a nitric acid coverage of ∼7.5 × 10 14 molecules/cm 2 or ∼ 1 monolayer. This coverage suggests that the hydrolysis reaction is limited to the surface or near-surface region of ice at these low temperatures.

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Section: Laser-induced Thermal Desorption (Litd)mentioning

confidence: 99%

Surface Sensitive Studies of the Reactive Uptake of Chlorine Nitrate on Ice

1997

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“…A similar model has been used recently to interpret the behavior of NH3 on MgO( 100) . 17 To calibrate the coverage in the photodissociation experiments, the adsorption behavior of methyl iodide on MgO( 100) has been studied by TPD using laser ionization with time-of-flight mass spectrometry (TOFMS) detection. The same three coverage regimes described above have been observed.…”

Section: Introductionmentioning

confidence: 99%

257 nm photoinduced chemistry of methyl iodide adsorbed on MgO(100)

Trentelman

Fairbrother

Strupp

et al. 1992

The Journal of Chemical Physics

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The 257 nm photochemistry ofCD 3 I adsorbed on MgO( 1(0) has been investigated. The photo fragments ejected along the surface normal were probed using resonantly enhanced multi photon ionization spectroscopy coupled with time-of-flight mass spectrometry. Methyl radicals and atomic iodine fragments in both the ground Ie P 3/2 ) = I and spin-orbit excited lepl/ 2 ) =1* states were observed as direct photofragments produced at the surface. Laserinduced desorption of methyl iodide competes with dissociation at the surface. The total cross section for removal of adsorbed CD31 from the surface at 257 nm is comparable to the gas phase cross section. A significant portion of the atomic iodine fragments remain trapped at the surface with preferential trapping of 1*. Additionally, nonresonant I + and 1 2 + signals were detected and initially observed to increase as a function of the irradiation time and then decrease with further irradiation. This behavior is shown to be indicative of photoinduced production and photoinduced removal of a surface intermediate. A surface reaction mechanism and the existence of a common precursor resulting from the interaction of adsorbed atomic iodine with adsorbed methyl iodide or methyl iodide clusters is postulated.

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“…This allows us to partially justify the assumption regarding the independence of the dynamical shift and broadening with respect to the defects. (iv) The surface corrugation experienced by ammonia is sufficiently large to prevent diffusion of the molecules [24]. Although it is clearly antagonistic with the idea that probe diffusion toward the defect should reinforce the defect signature, this was a willing choice here to demonstrate that this signature can even be observed in an unfavorable situation where the molecules do not move from their deposition site and to avoid situations which would lead to their chemisorption on the defects after migration on the surface.…”

Section: Discussionmentioning

confidence: 99%