Vibrational response of surface adsorbates to femtosecond substrate heating

Culver, Joseph P.; Li, M.; Jahn, L. G.; Hochstrasser, Robin M.; Yodh, Arjun G.

doi:10.1016/0009-2614(93)85661-7

Cited by 39 publications

(30 citation statements)

References 31 publications

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“…The lifetimes of vibrationally excited molecules at surfaces are in the order of picoseconds. [93][94][95] Clearly the accommodation of the normal and parallel velocity has to occur on a much shorter time scale, in fact a few femtoseconds because the quenching, in this case molecular chemisorption, probability is on the order of 10 Ϫ3 . For both the normal velocity and the parallel velocity this implies far too fast accommodation, in spite of the presence of a very corrugated chemisorption well.…”

Section: Discussionmentioning

confidence: 99%

O2 transient trapping-desorption at the Ag(111) surface

Raukema

Butler

Kleyn

1997

The Journal of Chemical Physics

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Molecular beam scattering experiments of O2 from Ag(111) carried out at a surface temperature of 150 K, which is below the desorption temperature for the molecular chemisorption state, show three different scattering paths: physisorption followed by desorption, direct-inelastic scattering and transient trapping-desorption. The transient trapping-desorption process is attributed to transient adsorption of the molecule in a metastable O2δ− state at the surface. The translational desorption energy of the transiently trapped molecules is far above thermal, strongly dependent on the surface temperature and independent of the translational energy and angle of the incident oxygen molecule. A strongly peaked intensity distribution around the surface normal is observed for the desorption. The transient trapping probability shows a sharp increase above a threshold energy and a subsequent decrease with increasing incidence energy. It is accompanied by a strong broadening in the angular direct-inelastically scattered flux distribution. The possible origin of the metastable O2δ− state will be discussed.

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Section: Discussionmentioning

confidence: 99%

O2 transient trapping-desorption at the Ag(111) surface

Raukema

Butler

Kleyn

1997

The Journal of Chemical Physics

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“…Frustrated translational vibrations are considered particularly important in surface chemistry because they are typically very low in energy (a few meV) and are thus thermally activated. This mode has been found to be extremely short-lived for CO on copper, with a lifetime in the few picosecond range [4][5][6]. The mechanisms governing the relaxation of this mode are of considerable interest.…”

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confidence: 99%

Substrate-Adsorbate Coupling in CO-Adsorbed Copper

Lewis

Rappe

1996

Phys. Rev. Lett.

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The vibrational properties of carbon monoxide adsorbed to the copper (100) surface are explored within density functional theory. Atoms of the substrate and adsorbate are treated on an equal footing in order to examine the effect of substrate-adsorbate coupling. This coupling is found to have a significant effect on the vibrational modes, particularly the in-plane frustrated translation, which mixes strongly with substrate phonons and broadens into a resonance. The predicted lifetime due to this harmonic decay mechanism is in excellent quantitative agreement with experiment.An important consequence of molecular adsorption to a metal surface is the emergence of new, low-frequency vibrations associated with fluctuations of the chemisorption bond. These "external modes" correspond to translations and rotations of the free molecule which become frustrated upon adsorption to a substrate. They play an instrumental role in many fundamental processes at surfaces, including chemical reactivity, desorption, and surface diffusion [1][2][3], and are, therefore, of intense scientific interest.In this letter, we theoretically investigate the vibrational dynamics of in-plane frustrated translational (FT) motion for a prototypical adsorbed system: carbon monoxide on the (100) surface of copper at halfmonolayer coverage. Frustrated translational vibrations are considered particularly important in surface chemistry because they are typically very low in energy (a few meV) and are thus thermally activated. This mode has been found to be extremely short-lived for CO on copper, with a lifetime in the few picosecond range [4][5][6]. The mechanisms governing the relaxation of this mode are of considerable interest.The present study focuses on the role of the substrate lattice in FT decay. Vibrational states for the combined substrate-adsorbate system are computed from first principles, with all atoms treated on an equal footing. These investigations reveal that the dominant contribution to FT relaxation comes from resonant mixing of frustrated translations with long-wavelength bulk copper phonons. This is a purely harmonic mechanism, and it gives rise to a computed lifetime in good quantitative agreement with experiment [4]. To our knowledge, this is the first detailed, quantum-mechanical investigation for an adsorbed metal system that demonstrates the strong interaction between adsorbate motion and long-wavelength bulk phonons. An earlier classical model of FT damping [7] considered this type of coupling for the case of an isolated FT oscillator attached to a semi-infinite, elastic medium. The damping was expressed as a macroscopic frictional force. Other microscopic theoretical studies have primarily considered only anharmonic effects in addressing adsorbate-lattice vibrational coupling, and have failed to identify this resonance because they have not modeled a large enough portion of the substrate to accommodate the long-wavelength phonons involved in resonant harmonic mixing.Carbon monoxide on the (100) surface of copper has been ...

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“…The laser system is described in detail in references [3,5]. Briefly, the system is based on a Nd:Ylf oscillator and involves two tunable synchronously pumped dye lasers and a regenerative amplifier.…”

Section: Methodsmentioning

confidence: 99%

“…These experiments however do not addressed the role of an excited substrate. In this contribution we report results of experiments in which IR vibrational spectroscopy is used to resolve the response of molecularly adsorbed CO on a Cu(1 11) substrate to a 300fs visible heating pulse [3]. We fmd that a low frequency CO mode couples to both the substrate electrons and phonons, and that the representative coupling rates can be separately determined [3,4].…”

Section: Introductionmentioning

confidence: 99%

<title>Infrared response of chemisorbed CO to femtosecond metal substrate heating</title>

Yodh

Culver

et al. 1994

SPIE Proceedings

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Time resolved infrared spectroscopy is used to monitor the stretch mode of CO on Cu(11 1) following femtosecond visible excitation. A time dependent shift in the stretch mode complex frequency is observed and is attributed to low frequency adsorbate-like modes becoming excited via coupling to substrate electrons and phonons. At low levels of excitation it is found that the frustrated translation is coupling to the bulk electron reservoir with a rate ; 167 (24) GHZ, and to the bulk phonon reservoir with a rate = 145 (56) GHz. At higher excitation levels deviations from the model are observed.

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Vibrational response of surface adsorbates to femtosecond substrate heating

Cited by 39 publications

References 31 publications

O2 transient trapping-desorption at the Ag(111) surface

O2 transient trapping-desorption at the Ag(111) surface

Substrate-Adsorbate Coupling in CO-Adsorbed Copper

<title>Infrared response of chemisorbed CO to femtosecond metal substrate heating</title>

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