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  • 1
    Electronic Resource
    Electronic Resource
    Vibrational energy relaxation of a polyatomic adsorbate on a metal surface: Methyl thiolate (CH3S) on Ag(111) (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 2438-2448 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The lifetime of the first excited level of the symmetric C-H stretching mode of methyl thiolate (CH3S) bonded to Ag(1 1 1) is measured by populating the level with a picosecond infrared pulse and probing the population by transient sum frequency generation spectroscopy. The population transient shows a biexponential decay across the experimental temperature range from 110 to 380 K. The fast decay component has a lifetime of 2.5–3 ps at all temperatures. The slow relaxation component lifetime varies from 55 ps at 380 K to 90 ps at 110 K. Neither relaxation component shows decay rates that are compatible with direct energy transfer to phonons or electron-hole pairs of the metal substrate. Both relaxation components are instead assigned to intramolecular energy transfer to excited vibrational levels of other vibrational modes of the molecule.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459867
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  • 2
    Electronic Resource
    Electronic Resource
    Vibrational energy relaxation in a molecular monolayer at a metal surface (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 3878-3879 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Picosecond time-resolved measurements of vibrational energy relaxation from ν=1 to ν=0 for C–H stretching modes of the terminal methyl group in 9 Cd stearate Langmuir–Blodgett monolayer on an evaporated silver film were made. The experiments used infrared–visible sum spectroscopy to dynamically probe vibrational level populations. To the authors' knowledge, this is the first direct measurement of vibrational energy relaxation for molecular adsorbates at a bulk metal surface. Multicomponent decay processes with lifetimes of 3 ps to 〉1 ns indicate complex intramolecular vibrational energy transfer processes in these ordered monolayer films, which may be different than for similar molecules in liquids.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455795
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  • 3
    Electronic Resource
    Electronic Resource
    Vibrational energy transfer of CO/Cu(100): Nonadiabatic vibration/electron coupling (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 3950-3956 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Vibrational energy relaxation of the internal C–O stretching mode of carbon monoxide in the c(2×2) overlayer on the Cu(100) surface at 120 K is measured by picosecond pump–probe spectroscopy. A resonant 1.5 ps infrared pulse at ν=2085 cm−1 pumps the C–O stretching mode. The energy relaxation is monitored by sum frequency generation from a delayed pair of 1.5 ps infrared and visible pulses. A single component decay, with a decay time of 2.0 ±0.5 ps, is reported. Uncertainties in the actual excited state lifetime are discussed, and the actual lifetime is estimated to be 2.0 ±1.0 ps. This lifetime is close to the lower limit of 1.2 ps set by the observed vibrational linewidth of 4.5 cm−1. The energy relaxation process is interpreted to occur by nonadiabatic energy transfer to the electrons (electron-hole pair excitations) of the copper substrate, and the measurement supports previous assertions that the nonadiabatic energy transfer rate for this system is very rapid. The nonadiabatic energy transfer lifetime of this mode has previously been estimated by density-functional calculations [T. T. Rantala and A. Rosen, Phys. Rev. B 34, 837 (1986)], and has recently been calculated by extrapolation of ab initio Hartree–Fock electronic structure calculations for CO on copper clusters [M. Head-Gordon and J. Tully, preceding paper, J. Chem. Phys. 96, 3939 (1992)]. The calculated lifetimes in both cases are in the 1–3 ps range, in good agreement with the experimentally measured value.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461897
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  • 4
    Electronic Resource
    Electronic Resource
    Vibrational energy transfer on hydrogen-terminated vicinal Si(111) surfaces: Interadsorbate energy flow (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 6203-6212 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report measurements of excited-state lifetimes for Si–H stretching vibrational modes of steps and terraces on chemically prepared, hydrogen-terminated vicinal Si(111) surfaces using picosecond pump–probe surface spectroscopy. The steps present on these vicinal surfaces are shown to play an important role in the vibrational energy relaxation pathways. Three types of vicinal Si(111) surfaces are studied, all having monohydride-terminated terraces but differing in step termination or in step density. Two surfaces are cut along the 〈1¯1¯2〉 direction, 9° and 5° from the (111) plane, respectively. Both of these surfaces have dihydride-terminated steps. A third surface is cut 9° from the (111) plane along the 〈112¯〉 direction and has monohydride-terminated steps. Two normal modes of the dihydride-terminated steps show vibrational energy relaxation times of ∼100 ps [≤80 ps and 130(20) ps, uncertainty in parentheses], while the monohydride-terminated steps relax 10 times more slowly with an 1100(120) ps lifetime. On the dihydride-stepped 9° surface the lifetime of the terrace mode is shortened to 420(40) ps from the flat surface lifetime of 950(100) ps, while on the monohydride-stepped surface the terrace mode lifetime is 820(80) ps. The results are explained by energy transfer between the terrace and the step Si–H modes. The different dynamics on the monohydride- and dihydride-stepped surfaces arise because the short-lifetime dihydride steps act as energy drains, while the long-lifetime monohydride steps do not. Dipole–dipole coupling between the Si–H stretching modes can account for the interadsorbate vibrational energy transfer observed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462637
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  • 5
    Electronic Resource
    Electronic Resource
    Surface vibrational energy relaxation by sum frequency generation: Five-wave mixing and coherent transients (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 2449-2457 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Vibrational energy relaxation of molecular adsorbates at solid surfaces has been measured in several recent experiments by pumping vibrational transitions with resonant picosecond infrared laser pulses and probing the excited state vibrational populations with transient infrared–visible sum frequency generation (SFG). In this paper, we develop a description of the infrared-pump, SFG-probe experiment as a five-wave mixing process in the perturbation limit. Five-wave mixing describes the effect of finite vibrational coherent response times (T2) on the experimental time resolution and includes coherent interactions between the pump and probe infrared fields which contribute to transient coherent artifacts in the experimental signal. Neither of these effects is included in the previous steady state descriptions of the SFG vibrational probe. The five-wave mixing expression is developed for a three-vibrational-level model of the adsorbate molecule and is integrated numerically for Gaussian pulse shapes to illustrate the effects of coherent artifacts and to compare these artifacts with those observed in pump–probe absorption experiments, which are described by four-wave mixing. Numerical simulations of the three-level response for a recent measurement of the surface vibrational energy relaxation of methyl thiolate/Ag(111) illustrate the use of the five-wave mixing expression to distinguish unambiguously between rapid energy relaxation and coherent artifacts in the experiment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459868
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  • 6
    Electronic Resource
    Electronic Resource
    Electronic states of semiconductor clusters: Homogeneous and inhomogeneous broadening of the optical spectrum (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 4001-4011 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The homogeneous (single-cluster) and inhomogeneous contributions to the low temperature electronic absorption spectrum of 35–50 A(ring) diameter CdSe clusters are separated using transient photophysical hole burning. The clusters have the cubic bulk crystal structure, but their electronic states are strongly quantum confined. The inhomogeneous broadening of these features arises because the spectrum depends upon cluster size and shape, and the samples contain similar, but not identical, clusters. The homogeneous spectrum, which consists of a peak 140 cm−1 (17 meV) wide, with a phonon sideband and continuum absorption to higher energy, is compared to a simple molecular orbital model. Electron–vibration coupling, which is enhanced in small clusters, contributes to the substantial broadening of the homogeneous spectrum. The inhomogeneous width of the lowest allowed optical transition was found to be 940 cm−1, or seven times the homogeneous width, in the most monodisperse sample.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454833
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  • 7
    Electronic Resource
    Electronic Resource
    Vibrational energy transfer among adsorbate modes: Picosecond dynamics on stepped H/Si(111) (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 6114-6125 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Direct measurements of interadsorbate vibrational energy flow among Si–H stretching modes on hydrogen-terminated, stepped vicinal H/Si(111) surfaces are made. A two-color picosecond infrared method is used in which one vibrational mode is pumped by a resonant infrared pulse and other vibrational modes are probed by vibrationally resonant sum frequency generation to observe energy transfer. The surfaces are prepared by chemical etching in HF solutions and have monohydride-terminated (111)-(1×1) terraces, and average terrace widths of approximately five atoms. Two types of surfaces, differing in having either monohydride- or dihydride-terminated steps, are examined. The results on both surfaces confirm that interadsorbate energy transfer competes efficiently with energy relaxation to the substrate. On the dihydride-stepped surface, the energy flow is analyzed to give a relatively complete kinetic model of the energy equilibration pathways. The model confirms that the fast relaxing dihydride-terminated steps (60–120 ps lifetime) drain a large fraction (∼2/3) of the terrace Si–H mode energy (the terrace mode intrinsic lifetime is fit to be ∼1.4 ns). The model is consistent with terrace–step energy transfer by dipole–dipole coupling between Si–H oscillators. On the monohydride-stepped surface, the experimental results suggest even stronger terrace–step coupling, but the monohydride step lifetime is long ((approximately-greater-than)500 ps) and does not drain the terrace mode energy. The coupling of the monohydride steps to the terraces by dipole interactions is in fact calculated to be strong enough so that the step and terrace modes mix, and detailed kinetic analysis of the monohydride-stepped surface is therefore ambiguous because of strong spectral interactions of the modes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465907
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  • 8
    Electronic Resource
    Electronic Resource
    Transient vibrational mode renormalization in dipole-coupled adsorbates at surfaces (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 6896-6906 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Dipole interactions among adsorbates at solid surfaces can strongly affect the intensities, positions, and line shapes of vibrational resonances. An understanding of these effects has been important in spectroscopic investigations of surface structure. Here, the adsorbate dipole interactions are shown to create transient spectral intensity and resonance position changes when vibrational modes are excited in ultrafast pump–probe laser experiments at surfaces. The spectral changes occur because the intensities and positions of vibrational resonances are dependent upon the magnitude of interadsorbate dipole interactions, and vibrational excitation modifies the effective oscillator dynamic dipoles that determine these interactions. The vibrational modes are different (renormalized) after excitation because of the change in coupling. The effects account for unusual spectral transients observed in recent pump–probe experiments on the Si–H stretching modes of vicinal H/Si(111) surfaces [K. Kuhnke, M. Morin, P. Jakob, N. J. Levinos, Y. J. Chabal, and A. L. Harris, J. Chem. Phys. 99, 6114 (1993)]. The predicted effects serve as a novel time-resolved probe of the strength of dipolar interactions in adsorbate layers, and will arise in any adsorbate layer where the vibrational dynamic dipole interactions are large enough to cause spectral intensity borrowing among different adsorption sites or different adsorbates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.467005
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  • 9
    Electronic Resource
    Electronic Resource
    The Nature of Simple Photodissociation Reactions in Liquids on Ultrafast Time Scales (1988)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Physical Chemistry 39 (1988), S. 341-366 
    Details
    ISSN: 0066-426X
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.pc.39.100188.002013
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  • 10
    Electronic Resource
    Electronic Resource
    Structural Characterization of Self-Assembled Multilayers by FTIR (1994)
    s.l. : American Chemical Society
    Chemistry of materials 6 (1994), S. 122-126 
    Details
    ISSN: 1520-5002
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/cm00038a006
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