Laser induced desorption of NO from NiO(100): Characterization of potential energy surfaces of excited states

Klüner, Thorsten; Freund, Hans‐Joachim; Freitag, J.; Staemmler, Volker

doi:10.1016/s1381-1169(96)00479-7

Cited by 30 publications

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“…Therefore, rotation has to be taken into account in the simulations. The azimuthal corrugation is small for all excited states, but the potentials are strongly anisotropic with respect to the polar angle a [13]. This requires an explicit treatment of this coordinate.…”

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“…Earlier studies have shown that the global shape of the surface can be understood as being due to Coulomb attraction between NO 2 and the positive hole created within the cluster upon charge transfer and the Pauli repulsion between the NO 2 and the O 22 anions of the surface [13]. The minimum of the excited state PES is located at a smaller molecule-surface distance than in the ground state (Antoniewicz-like [15] desorption scenario) and the NO 2 -like intermediate prefers an upright position at moderate distances, in contrast to the tilted equilibrium geometry of the electronic ground state [13].…”

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Theoretical Investigation of Laser Induced Desorption of Small Molecules from Oxide Surfaces: A First Principles Study

et al. 1998

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State resolved laser induced desorption of NO molecules from a NiO(100) surface is studied theoretically. A full potential energy surface for the excited state was constructed by means of ab initio cluster calculations in addition to the potential energy surface for the ground state. Multidimensional wave packet calculations on these two surfaces allow a detailed simulation of experimental observables, such as velocity distributions and desorption probabilities, on a full ab initio basis.[S0031-9007 (98)06374-1] PACS numbers: 79.20.La, 71.10.LiState resolved laser induced desorption of small molecules from well-characterized surfaces has been the subject of numerous experimental studies in recent years [1], but a detailed understanding even of basic features of final state distributions of the desorbing molecules still remains a challenge. Many theoretical investigations have been reported for the description of such DIET (desorption induced by electronic transitions) processes in which either classical [2,3] or quantum mechanical [4-7] simulations of nuclear motion of the desorbing molecules are presented. All dynamical simulations so far have been empirical because of the lack of sufficiently accurate ab initio potential energy surfaces, especially for the electronically excited states. In this paper, we present a full ab initio potential energy surface (PES) for an excited state involved in a DIET process. As an example, we have studied the system NO͞NiO(100) for which velocity distributions for different vibrational ͑y 00 ͒ and rotational ͑J 00 ͒ states of the desorbing NO molecules are shown in Fig. 1 [8]. By performing three-dimensional wave packet calculations on the PESs of the ground and excited electronic states, we can generate the respective distributions.The method of calculation of the electronically excited states uses a NiO 5 82 cluster embedded in a semi-infinite Madelung potential of point charges 62 to simulate the NiO(100) surface [9]. The NO molecule is adsorbed at an on-top position above a Ni 21 cation. The ground state is characterized by an equilibrium geometry with a tilt angle a of 45 ± of the molecular axis with respect to the surface normal. This is in perfect agreement with the experiment [10]. The excited states relevant for laser induced desorption turn out to be charge transfer states of the NO͞NiO(100) system, where one electron is transferred from the cluster to the NO molecule resulting in an NO 2 -like intermediate. These states of the adsorbate/ substrate system are calculated by a configuration interaction (CI) calculation in the valence space of the O2p-, Ni3d-, and NO2p-orbitals. Details on the construction of the reference configuration, the generation of the CI space, and selection of a representative excited state are described in Refs. [9,11].A PES for a representative NO 2 -like excited state is constructed in which the distance R of the center of mass of the NO molecule and the tilt angle a are varied. The internal N-O distance is kept fixed at the NO gas phase value...

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Theoretical Investigation of Laser Induced Desorption of Small Molecules from Oxide Surfaces: A First Principles Study

et al. 1998

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“…The bath TLSs thus describe the surface electron hole pairs and the bath Hamiltonian is hence given by [11,25] (12) In the above equationσ † i andσ i are the creation and annihilation operators for the ith TLS, respectively, and (NN) stands for the nearest neighbour. The surface electron-hole pairs are relatively localised at the corresponding Ni-O pairs in the lattice [39], between which charge transfer can occur. This is described by the first term in Equation (12).…”

Section: The Surrogate Hamiltonian Applied To Laser-induced Desorptiomentioning

confidence: 99%

“…a 0 denotes the distance between the nickel and oxygen atoms, the sites within each surface layer are labelled n and the layers are labelled with m, e.g., n = 0, m = 0 labels the surface dipole located directly below the CO molecule in the uppermost surface layer and n = 2, m = 1 labels the surface dipole in the second surface layer located two atom rows to the left/right of the CO molecule. μ(R) denotes the transition dipole moment of the primary system and q is the dipole charge, determined by the completeness of charge transfer between a nickel and an oxygen atom, which has been estimated to q ≈ 0.25 from ab initio calculations [45].…”

Section: The Surrogate Hamiltonian Applied To Laser-induced Desorptiomentioning

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A Surrogate Hamiltonian study of femtosecond photodesorption of CO from NiO(100)

Asplund

Klüner

2013

Molecular Physics

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In this paper, the Surrogate Hamiltonian approach is employed in order to study electronic relaxation in femtosecond laserinduced desorption experiments of CO from NiO(100). The study is based on ab initio calculations and a microscopic description of the NiO(100)-surface and the relaxation mechanism developed by Koch et al. The relaxation mechanism is assumed to be of dipole-dipole interaction nature, where the transition dipole moment of the adsorbate interacts with surface electron-hole pairs. In the Surrogate Hamiltonian approach the electron-hole pairs are treated as two-level systems and are described by excitation energy and a dipole charge. The Surrogate Hamiltonian parameters and potential energy surfaces used are obtained from ab initio calculations. The desorption probability and the velocity distributions of the desorbing molecules are calculated and an excited state lifetime is predicted. Throughout this paper atomic units, i.e. = m e = e = a 0 = 1, have been used unless otherwise stated.

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“…Therefore, NO C ions formed at the surface ( Fig. 1) may escape, whereas the postulated NO ions as intermediate 9 for field-free desorption may be further quenched electronically. The ionization of an adsorbed NO molecule (ionization energy: 9.26 eV) is experimentally accessible by a two-photon process if 6.4 eV photons from an excimer laser are employed.…”

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Photon‐induced field desorption of NO from Rh

Drachsel

Teutsch

2007

Surface & Interface Analysis

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The effect of an electric field on the NO photo-desorption from Rh was investigated using a pulsed laser atom probe. Experiments were carried out at 78 K by irradiating a [111] oriented Rh field-emitter tip and a Rh single crystal of 1.4 mm diameter at 6.4 eV and at 3.2 eV photon energy. The energies and masses of the emitted ions were evaluated from time-of-flight (ToF) measurements. For 6.4 eV irradiation of the Rh tip, a quadratic yield dependence on the laser fluence has been observed for NO. This is interpreted as a two-photon ionization of field-adsorbed NO; this is supported by the same behavior of O 2 and Xe but at a comparatively lower yield. In cases where the ionization energy of the probed species (Ar, N 2 , CO) is higher than 12.8 eV no such effect is observed. Laser irradiation with 2.3 eV photons initiates thermally assisted field desorption of the species at a comparatively higher fluence. Ion energy analysis suggests re-neutralization of NO + in the forbidden zone, but the translational energy gained appears to be sufficient to overcome the desorption barrier and field ionizion at the critical distance becomes probable. At low laser fluence a weak linear photo-desorption process has been detected, presumably caused by substratemediated electronic excitation as a first step. In this model, the photo-desorbed NO will subsequently be field-ionized, and accelerated away by the field. For the Rh single crystal, NO photo-desorption, with two-photon ionization in a second step, is deduced as the most probable mechanism.

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Laser induced desorption of NO from NiO(100): Characterization of potential energy surfaces of excited states

Cited by 30 publications

References 17 publications

Theoretical Investigation of Laser Induced Desorption of Small Molecules from Oxide Surfaces: A First Principles Study

Theoretical Investigation of Laser Induced Desorption of Small Molecules from Oxide Surfaces: A First Principles Study

A Surrogate Hamiltonian study of femtosecond photodesorption of CO from NiO(100)

Photon‐induced field desorption of NO from Rh

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