Laser-induced polymerization of submonolayer formaldehyde on silver (111)

Fleck, L. E.; Feehery, W. F.; Plummer, E. W.; Ying, Zhiliang; Dai, Houde

doi:10.1021/j100175a003

Cited by 30 publications

(45 citation statements)

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“…The desorption temperatures are 100 K for the multilayer and range between 106 and 110 K for the monolayer as the coverage increases from 20 L to 45 L. The observed desorption temperatures and coverage dependence are similar to that found by Fleck et al in their earlier studies of the CH 2 O/Ag (111) system. 11,13 These authors have also determined the desorption activation energy to be 6.2-6.7 kcal/ mol, depending on coverage, which is consistent with a physisorption interaction. Figure 2 compares TDS curves for the formaldehyde parent (mass 30) resulting from submonolayer coverage (22 L) at 85 K without exposure to UV light, and following irradiation at 266 nm (140 µJ/pulse, 2.1 × 10 4 shots).…”

Section: Methodsmentioning

confidence: 71%

“…Post-irradiation TDS curves, however, indicate extensive polymer formation for 355 nm excitation, as evidenced by the polymer breakup peak near 200 K. Fleck et al found polymer formation for UV wavelengths of 355 and 287 nm, but did not report any gas-phase products (including H 2 CO desorption) during UV exposure. [11][12][13][14][15] For 266 nm excitation, desorbed CO products were detected at fluences as low as 100 µJ/cm 2 and with sufficient yields to allow state-resolved velocity and rotational state distributions to be measured. These observations can be interpreted as a large increase in the CO formation cross section from 355 to 266 nm, similar to that found for polymerization and formaldehyde desorption.…”

Section: Methodsmentioning

confidence: 99%

“…In a recent series of papers, Fleck et al have shown that the UV-induced polymerization reaction is substrate mediated and suggest that polymerization proceeds via dissociative electron attachment (DEA) to yield O (a) atoms and CH 2(a) radicals. [11][12][13][14][15][16] The latter are expected to initiate polymerization of free monomers as observed in earlier studies involving preadsorbed O (a) atoms. 17,18 By comparison, DEA in the gas phase results in H -atoms and HCO radicals.…”

Section: Introductionmentioning

confidence: 99%

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State-Selective Laser Photochemistry of Formaldehyde on Ag(111)

et al. 1998

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State-selective (VUV + UV) resonant multiphoton ionization is used to measure the state-and energydistributions of the gas-phase products which accompany the UV photoinduced polymerization of formaldehyde on Ag(111). At 355 nm, only direct desorption of H 2 CO is observed, whereas both CO product formation and H 2 CO desorption are found at 266 nm. The rotational state and translational energies of the desorbed CO products exhibit a "fast" channel associated with a prompt fragmentation process and a "slow" channel in near-thermal equilibrium with the Ag surface. No gas-phase hydrogen products (H atoms, H 2 ) were detected during UV exposure, but H 2 desorption is observed during breakup of the polymer above 200 K. The timedependent desorption yields for both slow CO and H 2 CO are strongly temperature dependent and reflect the rate of polymerization. A simple kinetic model is used to describe the competing processes of desorption, fragmentation, and polymerization which ultimately result from the decay or fragmentation of an H 2 CO -(a) or other H 2 CO (a) excited-state species. In combination with depletion rates measured over the temperature range 30-95 K, the kinetic model results in an activation energy for polymerization of 0.90 ( 0.06 kcal/mol.

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Section: Methodsmentioning

confidence: 71%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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State-Selective Laser Photochemistry of Formaldehyde on Ag(111)

et al. 1998

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“…The group of H. L. Dai showed that laser radiation can be employed to initiate polymerization reactions on surfaces. 65,115,116 When formaldehyde on Ag (111) single crystal surfaces is irradiated with UV laser light the product polyoxymethylene could only be synthesized when the temperature of the surface was chosen appropriately due to the nature of the reaction steps involved. It was found that polymerization works best in a certain temperature interval.…”

Section: Towards Larger Molecules?mentioning

confidence: 99%

Initiation and control of catalytic surface reactions with shaped femtosecond laser pulses

Nuernberger

Wolpert

Weiß

et al. 2012

Phys. Chem. Chem. Phys.

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We report on femtosecond laser-induced catalytic reactions of carbon monoxide and hydrogen on single crystal surfaces under high vacuum conditions. Several product molecules are synthesized, among them also species for whose formation at least three reactants are required. By applying closed-loop optimal control, we manipulate these reactions and selectively optimize the ratio of different bond-forming reaction channels, in contrast to previous quantum control experiments aiming at bond-cleavage. Further experiments explore the nontrivial control mechanism and its sensitivity to the relative proportion of the two reactant gases.

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“…The adsorption structure and energetics of vinyl chloride on the Ag(111) surface, one of the few systems of molecules physisorbed on metal surfaces that have demonstrated substrate-mediated photochemical activity, [1][2][3] have been characterized 4 using Thermal Desorption Spectroscopy (TDS) and High Resolution Electron Energy…”

Section: Introductionmentioning

confidence: 99%