Polarization dependence in the UV laser desorption of NO from NiO(100)

Zacharias, H.; Eichhorn, G.; Schliesing, R.; Al‐Shamery, Katharina

doi:10.1007/s003400050672

Cited by 23 publications

(12 citation statements)

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“…Whether these states are populated directly in a localized optical excitation or diabatically via a substrate mediated process, or via both pathways, is still the subject of further investigations. 33 The polarization dependence of the cross section supports the conclusion of a dominant contribution of direct substrate-to-adsorbate charge transfer transitions to the excitation process. In a localized view the substrate shows octahedral symmetry, O h , in which all three Cartesian components of the transition dipole transform like t 1u .…”

Section: A Desorption Cross Sectionssupporting

confidence: 63%

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Femtosecond ultraviolet laser-induced desorption of NO from NiO(100)/Ni(100)

Eichhorn

Richter

Al‐Shamery

et al. 1999

The Journal of Chemical Physics

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We have studied the ultraviolet laser-induced desorption of NO molecules from an epitaxial film of NiO(100) on Ni(100) for pulse durations of 550 fs and at a photon energy of 3.95 eV. For applied laser intensities up to 450 MW/cm2, the highest intensities employed in this work, a linear dependence of the desorption yield on the laser intensity is observed. A desorption cross section of (1.9±0.3)⋅10−17 cm2 is then derived. The molecules are detected with rovibrational state selectivity by (1+1)-REMPI via the A 2Σ+(v′=0,1,2,3)←X 2Π(v″=0,1,2,3) γ-band transitions. The rotational population distributions are nonthermal, with rotational temperatures of about 290 K at low and of about 770 K at high rotational energies. The relative populations in the 2Π1/2 and 2Π3/2 fine-structure states and of the Λ-doublet states are examined for the given set of (v″,J″) quantum numbers. The vibrational states v″>0 are significantly populated approaching vibrational temperatures of 3800 K. Velocity distributions of the desorbed molecules are measured for individual rovibrational states. Bimodal distributions with a distinct rotational-translational coupling are observed. Further, molecules desorbing in the excited fine-structure state 2Π3/2 show a higher velocity than those desorbing in 2Π1/2 The results are compared with earlier ones obtained for the same system with nanosecond desorption pulses at hν=6.4 eV.

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Section: A Desorption Cross Sectionssupporting

confidence: 63%

“…33 The number of desorbed molecules can be estimated to be 3.3•10 Ϫ3 of the adsorbed particles per laser pulse. The NO molecules are adsorbed on top of the Ni ϩ ions having a distance of 2.94 Å.…”

Section: ͑1͒mentioning

confidence: 99%

Femtosecond ultraviolet laser-induced desorption of NO from NiO(100)/Ni(100)

Eichhorn

Richter

Al‐Shamery

et al. 1999

The Journal of Chemical Physics

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“…Measurements with different polarizations of the laser pulse found a dependence of the desorption yield on the polarization while the desorption velocities were not influenced. 55 If the excitation is mediated by the substrate, 1 the excitation energy is dissipated into the surface via electron-electron and ͑secondary͒ electron-phonon scattering. These multiple scattering events rule out a symmetry dependence of the excitation.…”

Section: The Interaction With the Laser Fieldmentioning

confidence: 99%

Surrogate Hamiltonian study of electronic relaxation in the femtosecond laser induced desorption of NO/NiO(100)

Koch

Klüner

Freund

et al. 2003

The Journal of Chemical Physics

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Electronic relaxation and ion desorption processes of solid Si(CH 3 ) 2 Cl 2 following Si 2p core-level excitation J. Chem. Phys. 106, 9105 (1997); 10.1063/1.474016 Two-dimensional wave packet studies of photon-stimulated desorption of NO from a metal surface induced by single and multiple electronic excitations A microscopic model for electronic quenching in the photodesorption of NO from NiO͑100͒ is developed. The quenching is caused by the interaction of the excited adsorbate-substrate complex with electron hole pairs (O 2p→Ni 3d states͒ in the surface. The electron hole pairs are described as a bath of two level systems which are characterized by an excitation energy and a dipole charge. The parameters are connected to estimates from photoemission spectroscopy and configuration interaction calculations. Due to the localized electronic structure of NiO a direct optical excitation mechanism can be assumed, and a reliable potential energy surface for the excited state is available. Thus a treatment of all steps in the photodesorption event from first principles becomes possible for the first time. The surrogate Hamiltonian method, which allows one to monitor convergence, is employed to calculate the desorption dynamics. Desorption probabilities of the right order of magnitude and velocities in the experimentally observed range are obtained.

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“…The direct optical excitation as modeled in Eq. (2) is justified by experiments which found a dependence of the desorption yield on the polarization of the laser light [11]. This dependence indicates that optical selection rules and hence the symmetry of the involved states are important.…”

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confidence: 73%

Femtosecond Photodesorption of Small Molecules from Surfaces: A Theoretical Investigation from First Principles

et al. 2003

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A microscopic model for the excitation and relaxation processes in photochemistry at surfaces is developed. Our study is based on ab initio calculations and the surrogate Hamiltonian method treating surface electron-hole pairs as a bath of two-level systems. Desorption probabilities and velocities in the experimentally observed range are obtained. The excited state lifetime is calculated, and a dependence of observables on pulse length is predicted. DOI: 10.1103/PhysRevLett.90.117601 PACS numbers: 79.20.La, 68.43.Tj Surface photochemistry occurs in many instances, including photocatalysis, atmospheric chemistry, and photochemical reactions at interstellar dust particles. Despite its ubiquitous nature, a microscropic understanding of the underlying basic processes remains a great challenge. In order to obtain a detailed mechanistic picture, the complexity of the studied systems and processes has to be reduced significantly. The simplest photochemical phenomenon on surfaces is laser-induced desorption of small molecules. Two-state models such as the Menzel-GomerRedhead or Antoniewicz scenarios [1] have proven useful to qualitatively understand the mechanism of DIET (desorption induced by electronic transitions). In both models, the excitation from the electronic ground to an excited state and the relaxation back to the ground state are modeled as vertical transitions. While significant progress has recently been made concerning reliable potential energy surfaces for DIET dynamics [2,3], excitation and relaxation mechanisms have been modeled only semiphenomenologically [4,5] assuming a separation of time scales of excitation, excited state nuclear dynamics, and quenching. Since electronic relaxation occurs on the time scale of femtoseconds [5], this assumption breaks down with the introduction of femtosecond laser pulses.Electronic relaxation is caused by the interaction of the excited adsorbate-substrate complex with electron-hole pairs in the surface [5]. In this Letter, we develop a microscopic model for this interaction assuming that electron-hole pairs can be described as a bath of twolevel systems (TLS). The surrogate Hamiltonian approach [6] is employed in which for a finite time the infinitely many TLS are approximated by a finite number. The finite time interval for which converged results can be obtained depends on the interaction strength and the number of TLS. This means that convergence is controllable and no further assumptions are needed. The surrogate Hamiltonian approach represents one possibility to treat a quantum system interacting with its environment.Since it does not rely on the approximation of weak coupling between system and environment and a separation of time scales of system dynamics and relaxation, it is particularly well suited to describe ultrafast charge transfer events in condensed phase [7]. In the present study, the construction of the bath is tailored to model electron-hole pairs in insulator and semiconductor surfaces. A particularly well studied example where quenching by ...

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Polarization dependence in the UV laser desorption of NO from NiO(100)

Cited by 23 publications

References 2 publications

Femtosecond ultraviolet laser-induced desorption of NO from NiO(100)/Ni(100)

Femtosecond ultraviolet laser-induced desorption of NO from NiO(100)/Ni(100)

Surrogate Hamiltonian study of electronic relaxation in the femtosecond laser induced desorption of NO/NiO(100)

Femtosecond Photodesorption of Small Molecules from Surfaces: A Theoretical Investigation from First Principles

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