Laser spectroscopy of desorbing molecules

Zacharias, H.

doi:10.1007/bf00619697

Cited by 62 publications

(7 citation statements)

References 109 publications

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“…In low pressure low temperature discharges, the most probable process behind the hot distribution is the recombinative desorption of hydrogen occurring at the wall of the discharge vessel [9]. This process strongly depends on the surface material, its temperature and the amount of atomic hydrogen or impurity particles present on the surface (see for example [34,35,36,37,38,39]) which makes a quantitative consideration very difficult.…”

Section: The Fulcher-α Transition Of Molecular Hydrogenmentioning

confidence: 99%

Determination of the rotational population of H2 and D2 including high-N states in low temperature plasmas via the Fulcher-α transition

Briefi

Rauner

Fantz

2017

Journal of Quantitative Spectroscopy and Radiative Transfer

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Vibrational and rotational excitation of the hydrogen molecule can significantly effect molecular reaction rates in low pressure low temperature plasmas, for example for the creation of H − /D − ions via the dissociative attachment process. In general, the rotational population in these discharges is known to be non-thermal with an overpopulation of states with high rotational quantum number N. In contrast to a sophisticated direct measurement of the rotational distribution in the X 1 Σ + g , v = 0 state, it is demonstrated that the determination can also be carried out up to high-N levels rather easily via optical emission spectroscopy utilizing the Fulcher-α transition of H 2 and D 2. The measured rotational populations can be described with a two-temperature distribution where the cold part reflects the population according to the gas temperature of the discharge. This has been verified by using the emission of the second positive system of nitrogen as independent gas temperature diagnostic. The hot part where the rotational temperature reaches several thousand Kelvin arises most probably from recombinative desorption of hydrogen at the discharge vessel wall where parts of the binding energy are converted into rotational excitation. Neglecting the hot population-what is often done when using the Fulcher-α transition as gas temperature diagnostic-can lead to a strong overestimation of T gas. No fundamental differences in the rotational distributions between hydrogen and deuterium have been found, only the hot rotational temperature is smaller for D 2 indicating an isotope-dependency of the recombinative desorption process.

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Section: The Fulcher-α Transition Of Molecular Hydrogenmentioning

confidence: 99%

Determination of the rotational population of H2 and D2 including high-N states in low temperature plasmas via the Fulcher-α transition

Briefi

Rauner

Fantz

2017

Journal of Quantitative Spectroscopy and Radiative Transfer

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“…The laser-induced desorption of small molecules from well characterized surfaces has been a matter of experimental investigations [1][2][3][4][5][6][7] and theoretical work for many years but the details of the mechanism are hardly understood, so that often only a rather qualitative picture is used to describe the fundamental processes.…”

Section: Introductionmentioning

confidence: 99%

Laser-induced desorption of NO from NiO(100): Ab initio calculations of potential surfaces for intermediate excited states

Klüner

Freund

Freitag

et al. 1996

The Journal of Chemical Physics

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In order to interpret the experimental results of the state resolved UV-laser-induced desorption of NO from NiO͑100͒ ͑rotational and vibrational populations, velocity distributions of the desorbing NO molecules, etc.͒, we have performed ab initio complete active space self-consistent field ͑CASSCF͒ and configuration interaction ͑CI͒ calculations for the interaction potential between NO and the NiO͑100͒ surface in the electronic ground state and for those excited states which are involved in the desorption process. The NiO͑100͒-NO distance and the tilt angle between the NO axis and the surface normal have been varied. A cluster model containing a NiO 5 8Ϫ-cluster embedded in a Madelung potential has been used for representing the NiO͑100͒ surface. The excited states which are important for the desorption process, are charge transfer states of the substrate-adsorbate system, in which one electron is transferred from the surface into the NO-2-orbital. The potential curves of these excited charge transfer states show deep minima ͑4 eV-5 eV͒ at surface/NO distances which are smaller than that in the ground state. The angular dependence of these potentials behaves similar as in the ground state. A semiempirical correction to the calculated excitation energies has been added which makes use of the bulk polarization of NiO. With this correction the charge transfer states are considerably stabilized. The lowest excitation energy amounts to about 4 eV which is in reasonable agreement with the onset of the laser desorption observed experimentally at about 3.5 eV. The density of the NO Ϫ-like states is rather high, so that probably several excited states are involved in the desorption process. The potential energy curves for all of these states are quite similar, but the transitions from the ground state into different excited charge transfer states show strongly differing oscillator strengths, which are also strongly dependent on the surface/NO distance. This fact is important for the dynamics of the deexcitation process in the sense of a selection criterion for the states involved. The magnitude of the oscillator strengths is large in comparison with the excitation of NO in the gas phase, which might be an indication for the possibility of optical excitation processes. One dimensional wave packet calculations on two potential energy curves using fixed lifetimes for the excited state in each calculation have been performed and enable us to estimate the mean lifetime of the excited state to be 15 fsрр25 fs. This implies that the dynamics of the system is dominated by the attractive part of the excited state potential.

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“…The experimental results have been well reproduced by calculations based on the kinetic theory of gas molecule-surface scattering [21,30]. On the other hand, vibrational heating has been observed in the associative desorption process of hydrogen from Cu and Pd surfaces [26][27][28]. This means that the vibrational excitation probability of associatively desorbing hydrogen is larger than that expected from the Boltzmann distribution at T s .…”

Section: Case Studiesmentioning

confidence: 53%

“…Rotational cooling has been observed in the associative desorption process of dissociative adsorption systems [26][27][28].…”

Section: Case Studiesmentioning

confidence: 99%

Surface as a Foundation to Realizing Designer Materials

Kasai

Diño

Kojima

et al. 2014

e-J. Surf. Sci. Nanotechnol.

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We entered the 21st Century witnessing several remarkable progress in Science and Technology. Novel materials and devices once considered stuffs of science fiction are, one after another, becoming reality. It would not be an exaggeration to say that we are coming to the Age of Designer Materials -Functional materials that have many varied and competing ground states, allowing us to switch the specific properties using external stimuli, e.g., heat, pressure, electric field, and magnetic field. Here, we present some non-traditional theoretical views developed in our group. The unifying themes are: quantum effects, complexity and functionality. We emphasize the unique role played by the Surface/Interface for providing a special environment (a foundation) for realizing Designer Materials, that are not realizable in the bulk and the strategic choice of particular elements as building blocks, e.g., for Exhaust Purification, Memory Devices and (Nano) Spintronics Applications.

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Laser spectroscopy of desorbing molecules

Cited by 62 publications

References 109 publications

Determination of the rotational population of H2 and D2 including high-N states in low temperature plasmas via the Fulcher-α transition

Determination of the rotational population of H2 and D2 including high-N states in low temperature plasmas via the Fulcher-α transition

Laser-induced desorption of NO from NiO(100): Ab initio calculations of potential surfaces for intermediate excited states

Surface as a Foundation to Realizing Designer Materials

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