Resonant infrared laser-induced desorption of methane condensed on NaCl(100): Isotope mixture experiments

Redlich, Britta; Zacharias, H.; Meijer, Gerard; Helden, Gert von

doi:10.1063/1.2159487

Cited by 19 publications

(10 citation statements)

References 25 publications

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“…In fact, on the basis of the principle of detailed balance, one might have predicted the lack of a vibrational effect in trapping from previous unsuccessful attempts to probe for the direct vibrational-induced desorption of physisorbed molecules from insulator 25 and metal 26 surfaces. The measurements have shown negligible desorption yields and a lack of isotope selectivity.…”

Section: ■ Discussionmentioning

confidence: 99%

The Negligible Role of C–H Stretch Excitation in the Physisorption of CH₄ on Pt(111)

et al. 2014

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We report a molecular beam study of the effect of vibrational excitation on the physisorption of methane on a Pt(111) surface. Our experiments use a continuous molecular beam of CH 4 , prepared in its antisymmetic C−H stretch mode ν 3 by infrared laser pumping via rapid adiabatic passage. Physisorbed CH 4 (ads) is detected on a Pt(111) surface by reflection absorption infrared spectroscopy. At a surface temperature of 77 K, the desorption lifetime of CH 4 (ads) is observed to be 0.4 ± 0.2 s. Trapping probabilities for the incident CH 4 are measured by the King and Wells beam reflectivity method with and without vibrational excitation. Vibrational excitation of the incident CH 4 with one quantum of ν 3 vibration does not produce a measurable effect (less than 0.2% change) on the trapping probability, in sharp contrast to the dissociative chemisorption process. The effect of resonant vibrational excitation of physisorbed CH 4 (ads) on its dissociation rate was also investigated. ■ INTRODUCTIONThe trapping of a gas-phase molecule into a weakly bound physisorbed state on a solid surface plays a central role in condensation processes as well as the initial step of chemisorption reactions via a precursor-mediated mechanism. It is well-established that the trapping probability decreases with increasing incident translational energy because any excess energy beyond the physisorption well depth needs to be transferred to surface degrees of freedom during the surface impact for trapping to occur. In the simplest case, the initial trapping probability depends only on the incident translational energy normal to the surface (normal energy scaling with E t · cos 2 θ) as described by the Baule model. 1 Madix et al. 2,3 have measured trapping probabilities for Ar and CH 4 on Pt(111) and concluded that in these two systems normal energy scaling is obeyed.The role of vibrational excitation of the incident molecule on the physisorption (trapping) probability is not yet wellunderstood, and experimental results reported to date in the literature differ for different molecules and surfaces. Sibener et al.4 studied the condensation coefficients of molecular beams of CCl 4 and SF 6 on their respective condensed phases at cryogenic temperatures. They observed a (small) decrease in the trapping probability with increasing rotational and vibrational excitation at low incident translational energy consistent with simple models of the trapping process. 5 On the other hand, Wodtke et al.6 studied the trapping of the diatomic NO in v = 0 and 2 on a Au(111) surface at 300 and 480 K. Using quantum state resolved detection of surface scattered NO by resonant multiphoton ionization they concluded that there was no measurable difference between the trapping probabilities for NO(v = 0) and NO(v = 2) for incident kinetic energies in the range of 0.1−0.75 eV. The fact that trapping was found to be insensitive to NO vibrational states was interpreted as being due to weak mechanical coupling between the high-frequency NO stretch and the low-f...

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Section: ■ Discussionmentioning

confidence: 99%

The Negligible Role of C–H Stretch Excitation in the Physisorption of CH₄ on Pt(111)

et al. 2014

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“…76 Recent experimental results support this theory 77 and we plan to explore the role of phonon excitation on methane activation more fully in a future publication. Inelastic tunnelling 11,44,78 or infrared excitation studies of surface-adsorbed species 79 differ in some ways from the beamsurface studies highlighted above, but key features of this framework still apply. The states available for excitation in these experiments are now eigenstates of the molecule surface complex, not those of an isolated gas-phase molecule.…”

Section: Impact Of Ivr On Surface Reactivity and Dynamicsmentioning

confidence: 99%

On the origin of mode- and bond-selectivity in vibrationally mediated reactions on surfaces

Killelea

Utz

2013

Phys. Chem. Chem. Phys.

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On the origin of mode-and bond-selectivity in vibrationally mediated reactions on surfaces. Physical Chemistry Chemical Physics, 15, 47: 20545-20554, 2013 The experimental observations of vibrational mode-and bond-selective chemistry at the gas-surface interface indicate that energy redistribution within the reaction complex is not statistical on the timescale of reaction. Such behavior is a key prerequisite for efforts to use selective vibrational excitation to control chemistry at the technologically important gas-surface interface. This paper outlines a framework for understanding the origin of non-statistical reactivity on surfaces. The model focuses on the kinetic competition between intramolecular vibrational energy redistribution (IVR) within the reaction complex, which in the long-time limit leads to statistical behavior, and quenching, scattering, or desorption processes that restrict the extent of IVR prior to reaction. Characteristic timescales for these processes drawn from studies of vibrational energy flow dynamics on surfaces and in the gas and condensed phases suggest that IVR is severely limited for important classes of surface reactions. Under these conditions, selective vibrational excitation can lead to preferential transition state access and result in mode-or bond-selective chemistry, even at high collision energies above the barrier to reaction. In addition to providing a basis for understanding experimental observations, the model provides guidance for identifying other gas-surface reactions that may exhibit mode-selective behavior.

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“…Furthermore, even without reactions, such energetic collisions will lead to the desorption of neutral species from the ice layer, as has been observed for vibrational resonant IRinduced desorption from molecular ices, like N2O, 51,52 CD3F, 53 and methane. 54 …”

Section: 50mentioning

confidence: 99%

Free-electron laser induced processes in thin molecular ice

et al. 2014

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Intermolecular reactions in and on icy films on silicate and carbonaceous grains constitute a major route for the formation of new molecular constituents in interstellar molecular clouds. In more diff use regions and in protoplanetary discs, energetic radiation can trigger reaction routes far from thermal equilibrium. As an analog of interstellar ice-covered dust grains, highly-oriented pyrolytic graphite (HOPG) covered with D2O, NO, and H atoms is irradiated by ultrashort XUV pulses and the desorbing ionic and neutral products are analysed. The yields of several products show a nonlinear intensity dependence and thus enable the elucidation of reaction dynamics by two-pulse correlated desorption.

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Resonant infrared laser-induced desorption of methane condensed on NaCl(100): Isotope mixture experiments

Cited by 19 publications

References 25 publications

The Negligible Role of C–H Stretch Excitation in the Physisorption of CH₄ on Pt(111)

The Negligible Role of C–H Stretch Excitation in the Physisorption of CH₄ on Pt(111)

On the origin of mode- and bond-selectivity in vibrationally mediated reactions on surfaces

Free-electron laser induced processes in thin molecular ice

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Resonant infrared laser-induced desorption of methane condensed on NaCl(100): Isotope mixture experiments

Cited by 19 publications

References 25 publications

The Negligible Role of C–H Stretch Excitation in the Physisorption of CH4 on Pt(111)

The Negligible Role of C–H Stretch Excitation in the Physisorption of CH4 on Pt(111)

On the origin of mode- and bond-selectivity in vibrationally mediated reactions on surfaces

Free-electron laser induced processes in thin molecular ice

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Product

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The Negligible Role of C–H Stretch Excitation in the Physisorption of CH₄ on Pt(111)

The Negligible Role of C–H Stretch Excitation in the Physisorption of CH₄ on Pt(111)