Infrared-laser excitation of the internal vibrational mode of a diatomic molecule adsorbed on a metal surface

Péremans, A.; Darville, J.; Gilles, J.-M.; George, Thomas F.

doi:10.1103/physrevb.35.2690

Cited by 10 publications

(4 citation statements)

References 30 publications

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“…Photodesorption usually requires less energy than LIlD, but shorter wavelengths (and sometime SPIICific photonic energies) in order to excite electronic transitions. metallic surfaces (21,23) and enhance LITO, but, to our knowledge, no photodesorption has been reported using infrared beams by a resonant excitation of specific vibrational modes of adsorbed molecules (24,25).…”

Section: Photochemical Effectsmentioning

confidence: 78%

Laser Processing of Metallic and Intermetallic Surfaces

Petit¹

1993

Materials and Manufacturing Processes

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The most common applications 01 the laser processing 01 metallic and intermetallic surfaces are presented. The advantages 01 this technology are deduced Irom the basic principles 01the interaction 01laser light w"h metallic materials. Applicetions, like superficial hardening and surface cleaning and alloying, are extensions 01 exi:rting processes beneming by the specific advantages 01laser annealing. Other ones, like de,position 01 passivating or wear·resistant coatings, exploit photochemical reactions induced in gas-phase or at metallic and semiconducting surfaces by UV or high intens"y laser beams.

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Section: Photochemical Effectsmentioning

confidence: 78%

Laser Processing of Metallic and Intermetallic Surfaces

Petit¹

1993

Materials and Manufacturing Processes

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“…The relaxation operator r(co) is frequency dependent, which reflects the memory in the time regression of two-time quantum correlation functions. In the time domain this would be a memory kernel, 8 and in the Markov approxi-mation F(co) assumes an ^-independent value. Furthermore, a Liouville operator Y(co) appears, which accounts for the fact that the density operator of the entire system does not factorize as padsorbate x Pcrystai in thermal equilibrium if the memory time is finite.…”

Section: Memory-induced Extra Resonances Of Adsorbatesmentioning

confidence: 99%

Memory-induced extra resonances of adsorbates

Arnoldus

George

1988

Phys. Rev. Lett.

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The optical absorption profile of an atom-surface vibrational bond is studied. From Markovian relaxation theory it follows that the line shape is a Lorentzian around the adsorbate resonance frequency coo. Dispersion relations for crystals have a fairly small cutoff frequency COD, which prohibits the use of such a simple theory. We calculated the spectral profile with finite-memory-time reservoir theory, and we found that the modified Lorentzian vanishes above COD. Also a new spectral line at COO + COD is predicted, which disappears in the Markovian limit. The physical origin of the new line is explained. 71.36.+C, 78.90,+t Adsorbed atoms on the surface of a crystal can absorb photons from an incident infrared laser beam. Coupling between the van der Waals bond and the radiation is brought about by the motion-induced dipole moment ju (the atom itself is assumed to be neutral for ir light), and the atom-crystal interaction is governed by the singlephonon coupling Hamiltonian * Hi--(ve z )dV/dz,Then an equation of motion for the reduced adsorbate density operator can be derived, in which the properties of the heat bath only enter parametrically, and can be expressed in terms of the Fourier-Laplace transform of the reservoir correlation function2) defines the dimensionless function g(z) in terms of the mass M of a bulk atom and the Debye frequency con. Then it can be shown that g(z) depends only on the dimensionless temperature y^ho^/k^T, with A:B Boltzmann's constant. An explicit expression for g(z) can be found elsewhere. 4 In the most simple theory of relaxation 5 one adopts the Markov and secular approximations, which yields for the low-intensity absorption line shape as a function of the laser frequency coin terms of the derivative of the binding potential well Viz). Here z denotes the normal direction to the surface (we neglect lateral motion) and u is the phononfield amplitude operator, 2 evaluated at the position of the surface atom which is closest to the adsorbate. Relaxation of the atomic bond due to phonon exchange with the crystal is most conveniently described with reservoir theory, where the crystal is regarded as a thermal bath. 3 j This profile is a Lorentzian with its peak value at 6)= s cao + alm[g((oo)+g*(~fi>o)l> and a half width at half-maximum equal to tfRe[g(o5o)+g*( -fiJo)]. The notation is S=CO/COD, COO^unperturbed adsorbate resonance, and «, = population of the ith level (n\>ri2). The temperature dependence is incorporated in g(z), and the phonon-coupling strength is measured byIn order to investigate this problem quantitatively, we have developed a finite-memory-time relaxation theory, 6 with no restriction on the time scales. Subsequently, we have applied this theory to the evaluation of the absorption line shape, with the formal result 7Most crucial for the derivation of the line profile (3) is the conjecture that the phonon-amplitude correlation function ([u(r)e z ](u-e z )> decays to zero very fast for r > 0, which would justify the Markov approximation. It is an essential feature ...

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“…(6.3) and evaluate the Laplace transform. We obtain f(lU)O"s = ILl I P a (.t;d l1ba +lU)J'kO"s kl ab (7.8) in terms of the Laplace transform!kl (lu) offkl (7) . Because L J equals the commutator with J' J, the right-hand side only involves operators J'I and projectors.…”

Section: Laplace Transformmentioning

confidence: 99%

“…For electron-hole pair formation the situation is even worse, where we have r7c ~ 1 so that a Markov approximation can never be justified. 7 There exist many relaxation theories. Most notable are the projection techniques, 8-10 a Langevin formulation, 2 and, as we adopt here, a reservoir approach.…”

mentioning

confidence: 99%

Correlation functions in finite memory-time reservoir theory

Arnoldus

George

1987

Journal of Mathematical Physics

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Articles you may be interested inTime-dependent exchange-correlation current density functionals with memory Time correlation functions for finite systems using secondquantized molecular time scale generalized Langevin equation theory: Effect of rotating wave approximationInteraction of a small system S with a large reservoir R amounts to thermal relaxation of the reduced system density operator Ps (t). The presence of the reservoir enters the equation of motion for p s (t) through the reservoir correlation functions fkl ( 'T) (defined in the text), which decay to zero for 'T ..... 00 on a time scale 'Tc' Commonly, this 'Tc is much smaller than the inverse relaxation constants for the time evolution of Ps (t). Then a series of approximations can be made, which lead to a Markovian equation of motion for Ps (t). In this paper the assumption of a small reservoir correlation time is removed. The equation of motion for p s (t) is solved, and it appears that the memory effect, due to 'Tc <#0, can be incorporated in a frequency dependence of the relaxation operator f(w). Subsequently, (unequal-time) quantum correlation functions of two system operators are considered, where explicit expressions for (the Laplace transform of) the correlation functions are obtained. They involve again the relaxation operator f(w), which accounts for the time regression. Additionally it is found that an initial-correlation operator Y(w) arises, as a consequence of the fact that the equal-time correlation functions do not factorize as Ps (t) times the reservoir density operator.It is pointed out that the frequency dependence of f (w) and the occurrence of a nonzero Y (w ) both arise as a result of'Tc <#0, and should therefore be treated on an equal footing. Explicit evaluation of f (w) and Y (w) shows that their matrix elements can be expressed entirely in ikl (w ), just as in the Markov approximation. Hence no essential complications appear if one should go beyond the limits of a small reservoir correlation time 'T c .

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Infrared-laser excitation of the internal vibrational mode of a diatomic molecule adsorbed on a metal surface

Cited by 10 publications

References 30 publications

Laser Processing of Metallic and Intermetallic Surfaces

Laser Processing of Metallic and Intermetallic Surfaces

Memory-induced extra resonances of adsorbates

Correlation functions in finite memory-time reservoir theory

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