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  • 2000-2004  (3)
  • 1990-1994  (5)
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  • 1
    Electronic Resource
    Electronic Resource
    A spectroscopic puzzle in ArHF solved: The test of a new potential (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 8009-8018 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The perturbed (v,b,K,n)=(1210),(1113)←(0000) band of ArHF is observed in a tunable laser/slit supersonic expansion spectrometer. The (1210) level correlates with j=2 rotation of the HF within the complex and therefore provides a test of high-order terms in a Legendre expansion of the intermolecular potential. Transitions to (1113) are observed due to intensity sharing with (1210), induced by a strong homogeneous (J-independent) perturbation that is analyzed quantitatively. The (1113) level has three quanta of Van der Waals stretch and thus probes the radial dependence of the potential close to the dissociation limit. The vibrational and rotational assignment is made possible by predictions based on the new H6(4,3,2) intermolecular potential of Hutson [J. Chem. Phys. 96, 6752 (1992)], which agree nearly quantitatively with experiment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463424
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  • 2
    Electronic Resource
    Electronic Resource
    A study of the structure and dynamics of the hydronium ion by high resolution infrared laser spectroscopy. III. The ν3 band of D3O+ (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 3257-3260 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: 294 transitions were measured by velocity modulation spectroscopy using a difference frequency laser system with a D2/O2 discharge and assigned to the ν3 (antisymmetric stretch) band of D3O+. A simultaneous analysis of this data with the ν2 band spectra reported by Sears, et al. [J. Chem. Phys. 83, 2676 (1985)] yielded a refined set of parameters for both the ground and the excited states of both bands. The ν3 bandcenters are 2629.6512(39) and 2624.2376(47) cm−1 for the s–s and a–a inversion components, respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457884
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Quantum yields for OH production from 193 and 248 nm photolysis of HNO3 and H2O2 (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 6935-6946 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The absolute quantum yields (Φ) for OH production from 193 and 248 nm photolysis of HNO3 and H2O2 are measured at room temperature using flash kinetic spectroscopy in a flow tube. The OH radicals are produced by excimer laser photolysis and probed via direct absorption of high resolution, tunable IR laser light. The resulting quantum yields are found to be ΦHNO3193=0.47±0.06, ΦH2O2193=1.22±0.13, ΦHNO3248=0.75 ±0.10, and ΦH2O2248= 1.58±0.23. These results indicate quantum yields for both precursors at both wavelengths which are less than the maximum possible values of 1 for HNO3 and 2 for H2O2. The present measurements are discussed in light of contrasting results suggested from other work.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.464735
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Stabilization and precise calibration of a continuous-wave difference frequency spectrometer by use of a simple transfer cavity (1994)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 65 (1994), S. 42-48 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A novel, simple, and inexpensive calibration scheme for a continuous-wave difference frequency spectrometer is presented, based on the stabilization of an open transfer cavity by locking onto the output of a polarization stabilized HeNe laser. High frequency, acoustic fluctuations of the transfer cavity length are compensated with a piezoelectric transducer mounted mirror, while long term drift in cavity length is controlled by thermal feedback. A single mode Ar+ laser, used with a single mode ring dye laser in the difference frequency generation of 2–4 μm light, is then locked onto a suitable fringe of this stable cavity, achieving a very small long term drift and furthermore reducing the free running Ar+ linewidth to about 1 MHz. The dye laser scan provides tunability in the difference frequency mixing process, and is calibrated by marker fringes with the same stable cavity. Due to the absolute stability of the marker cavity, precise frequency determination of near infrared molecular transitions is achieved via interpolation between these marker fringes. It is shown theoretically that the residual error of this scheme due to the dispersion of air in the transfer cavity is quite small, and experimentally that a frequency precision on the order of 1 MHz per hour is routinely obtained with respect to molecular transitions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1144744
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  • 5
    Electronic Resource
    Electronic Resource
    Nonexponential "blinking" kinetics of single CdSe quantum dots: A universal power law behavior (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 3117-3120 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Single molecule confocal microscopy is used to study fluorescence intermittency of individual ZnS overcoated CdSe quantum dots (QDs) excited at 488 nm. The confocal apparatus permits the distribution of "on" and "off" times (i.e., periods of sustained fluorescence emission and darkness) to be measured over an unprecedentedly large dynamic range (109) of probability densities, with nonexponential behavior in τoff over a 105 range in time scales. In dramatic contrast, these same τoff distributions in all QDs are described with remarkable simplicity over this 109-fold dynamic range by a simple inverse power law, i.e., P(τoff)∝1/τoff1+α. Such inverse power law behavior is a clear signature of distributed kinetics, such as predicted for (i) an exponential distribution of trap depths or (ii) a distribution of tunneling distances between QD core/interface states. This has important statistical implications for all previous studies of fluorescence intermittency in semiconductor QDs and may have broader implications for other systems such as single polymer molecules. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480896
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    Paper (German National Licenses)
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  • 6
    Electronic Resource
    Electronic Resource
    High-Resolution, Direct Infrared Laser Absorption Spectroscopy in Slit Supersonic Jets: Intermolecular Forces and Unimolecular Vibrational Dynamics in Clusters (1994)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Physical Chemistry 45 (1994), S. 367-399 
    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.45.100194.002055
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  • 7
    Electronic Resource
    Electronic Resource
    Molecular fluorescence in the vicinity of a nanoscopic probe (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 8596-8609 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The dramatic modifications of molecular fluorescence in the proximity of a sharp nanoscopic probe is investigated by an apertureless or antenna-based near-field scanning optical microscope, which exploits the interactions between a fluorescent sample and a laser illuminated Si atomic force microscope probe. Specifically, luminescence is monitored from evanescently excited, dye-doped polystyrene nanospheres (RS=20–80 nm) on a fused silica prism surface as a function of probe-sample geometry. The incident laser field is enhanced in the near-field of the probe tip, resulting in images with high sensitivity (σmin(approximate)2 Å2 in a 1 Hz detection bandwidth) and strongly subdiffraction-limited spatial resolution. At probe-sample distances greater than (approximate)λ/2, the images are dominated by far-field interference between (i) direct fluorescence from the molecular sample and (ii) indirect fluorescence from image dipoles induced in the atomic force microscope probe. Near-field "shadowing" of the molecular fluorescence by the probe also occurs and is studied as a function of probe-sample-detector geometry. Finally, effects of probe-sample proximity on the fluorescence emission spectrum are investigated. In summary, the data elucidate several novel near- and far-field molecular fluorescence enhancement effects relevant to further development of molecular and nanostructural spectroscopic methods with spatial resolution well below the diffraction limit. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1365931
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  • 8
    Electronic Resource
    Electronic Resource
    "On"/"off" fluorescence intermittency of single semiconductor quantum dots (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 1028-1040 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Single molecule confocal microscopy is used to investigate the detailed kinetics of fluorescence intermittency in colloidal II–VI (CdSe) semiconductor quantum dots. Two distinct modes of behavior are observed corresponding to (i) sustained "on" episodes (τon) of rapid laser absorption/fluorescence cycling, followed by (ii) sustained "off" episodes (τoff) where essentially no light is emitted despite continuous laser excitation. Both on-time and off-time probability densities follow an inverse power law, P(τon/off)∝1/τon/offm, over more than seven decades in probability density and five decades in time. Such inverse power law behavior is an unambiguous signature of highly distributed kinetics with rates varying over 105-fold, in contrast with models for switching between "on" and "off" configurations of the system via single rate constant processes. The unprecedented dynamic range of the current data permits several kinetic models of fluorescence intermittency to be evaluated at the single molecule level and indicate the importance of fluctuations in the quantum dot environment. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1377883
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