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  • Articles  (201)
  • 1990-1994  (201)
  • Physics  (151)
  • Chemistry and Pharmacology  (101)
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  • Articles  (201)
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  • 11
    Electronic Resource
    Electronic Resource
    Nonlinear line narrowing of excited state resonances in perylene doped poly(methylmethacrylate) using multiply enhanced nonparametric spectroscopy (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 1479-1486 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Line narrowing of perylene vibronic transitions in poly(methylmethacrylate) (PMMA) samples has been demonstrated using multiply enhanced nonparametric spectroscopy. Three lasers are used to generate a four wave mixing signal that is resonantly enhanced by three simultaneous perylene resonances involving a vibrational state, a vibrationless excited electronic state, and a vibronic state of the excited electronic state. There is a correlation between the position of the electronic and vibronic states within the inhomogeneously broadened absorption spectrum. The correlation can be used to achieve line narrowing by fixing one of the resonances to a subset of perylene sites within the inhomogeneous profile so the other resonance of those sites will be selectively enhanced. The position of the line narrowed vibronic peaks depends upon the electronic detuning from the center of the inhomogeneously broadened absorption band as different sites within the band are probed. Excited state coherent processes involving resonance with higher singlet states are shown to be unimportant from the detuning dependence on a simultaneous vibrational enhancement.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461063
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  • 12
    Electronic Resource
    Electronic Resource
    Simultaneous forward–backward Raman scattering studies of D2 broadened by D2, He, and Ar (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 7625-7633 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Unavoidable beam crossings within a spherical-mirror, multipass stimulated Raman gain cell give rise simultaneously to forward- and backward-scattering Raman signals. In the Doppler-broadened/Dicke-narrowed regime of density, the lineshape is a function of the momentum transfer in the scattering process and thus the observed spectra will have more complex lineshapes than those seen with simple forward or backward scattering geometries. The analyses necessary to quantitatively account for such forward–backward spectra are summarized. These spectra enable unique experimental tests of the lineshape functions used for the description of the Raman Q-branch spectrum under conditions where Doppler contributions and Dicke narrowing are significant. Results for the D2@B:D2 and D2@B:He systems support the well-known Galatry, or soft collision, lineshape function. However, in the case of D2@B:Ar, our results suggest the need to employ the more general, complex soft collision function. In addition, these studies have provided data on linear-with-density line broadening coefficients (previously published) and line shifting coefficients (reported here) for these molecular systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460149
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  • 13
    Electronic Resource
    Electronic Resource
    Emission spectroscopy of nitrogen in a supersonic discharge. Evidence of excited neutral nitrogen clusters (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 2564-2567 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Emission spectra indicating transient clusters in a supersonic nitrogen discharge are presented. Select spectral bands are attributed to emission from N2(C 3Πu,v'=0,1)–N2(X 1Σg+). The cluster transitions manifest as blue-degraded, blue-shifted sidebands of the second positive group due to emission from N2(C 3Πu). Results and significance concerning these previously undiscovered nitrogen clusters are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465073
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  • 14
    Electronic Resource
    Electronic Resource
    Gas distribution effects on electron cyclotron resonance deposition reactions (1994)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 65 (1994), S. 2968-2974 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The ability to produce high quality films in an electron cyclotron resonance reactor is dependent on the gas distribution system. In an effort to understand gas distribution effects, a variety of gas ring injection systems were implemented during silicon nitride growth. Film refractive index, uniformity, and stress were used to gauge each gas distribution system. As a result, we have demonstrated that evenly distributed gas injection systems are the most desirable producing uniform films. Film thickness uniformity was significantly influenced by the design of the gas ring as well as the gas flow. Theoretical models supported the observed results and identified desirable properties for gas ring distribution systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1144586
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  • 15
    Electronic Resource
    Electronic Resource
    A piston-actuated shock-tube, with laser–Schlieren diagnostics (1993)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 64 (1993), S. 1342-1346 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The essential construction features of a piston actuated shock tube are described, and its advantages relative to the conventional use of diaphragm ruptures for shock initiation are listed. Typical operational parameters are presented to illustrate the levels of reproducibility achieved. Tests with He and N2 drivers into ∼99% Ar (1.0%–0.1% reagent) covered shock speeds from 1.539±0.002–0.8143±0.002 mm/μs, corresponding to 2390–847K incident shock temperatures. Application of this tube for recording postshock front density gradients of the endoergic dissociation of ethane and the exoergic condensation of iron atoms via the laser–Schlieren technique is described.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1144090
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  • 16
    Electronic Resource
    Electronic Resource
    High spatial resolution infrared emission thermal measurement of laser-induced chemical vapor deposition (1992)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 3763-3766 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Infrared emission radiometry was used as a noncontact temperature probe with a tens of micron spatial resolution for monitoring laser-induced chemical vapor deposition (LCVD). With appropriate calibration of the emissivity, a temperature of 255±15 °C was measured during gold LCVD from dimethylhexafluoroacetylacetonate gold (III). Equivalent deposition temperatures were calculated for both continuous and modulated laser illumination. Depending on the deposition conditions, material deposited with a modulated laser beam varied from notably worse (due to stress cracking) to notably better (more uniform growth morphology) than material deposited with continuous laser illumination.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1143267
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  • 17
    Electronic Resource
    Electronic Resource
    Sources of error in a laser rangefinder (1994)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 65 (1994), S. 3165-3171 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We describe sources of error in a breadboard, low-cost, time-of-flight laser rangefinder. The rangefinder deduces the range of a retroreflecting target by directing an intensity-modulated laser beam at the target and measuring the phase difference between the returned and transmitted modulation envelopes. The phase measurement is performed by a combination of heterodyning and digital signal processing. We present an equation for the standard deviation of statistical errors generated by quantization in the digital signal processing. We show how both electrical crosstalk and stray light give rise to errors which are cyclic with target range, and we describe how these errors can be reduced. We demonstrate the importance of errors caused by the dependence of the photodiode's propagation delay upon the intensity and placement of the light spot incident upon its surface, and discuss how the instrument's optical components can be arranged to minimize such errors. Finally, we show that our rangefinder, using a modulation frequency of 140 MHz, has rms nonlinearity less than 85 μm.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1144545
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  • 18
    Electronic Resource
    Electronic Resource
    Structural Investigations of the Catalytic Mechanisms of Water Oxidation by the [(bpy)2Ru(OH2)]2O4+ Ion (1994)
    s.l. : American Chemical Society
    Inorganic chemistry 33 (1994), S. 4460-4467 
    Details
    ISSN: 1520-510X
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ic00098a010
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  • 19
    Electronic Resource
    Electronic Resource
    Pathways for water oxidation catalyzed by the (.mu.-oxo)bis[aquabis(bipyridine)ruthenium](4+) ion (1992)
    s.l. : American Chemical Society
    Inorganic chemistry 31 (1992), S. 1010-1017 
    Details
    ISSN: 1520-510X
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ic00032a017
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  • 20
    Electronic Resource
    Electronic Resource
    Denatured proteins inhibit translation in hemin-supplemented rabbit reticulocyte lysate by inducing the activation of the heme-regulated eIF-2.alpha. kinase (1993)
    s.l. : American Chemical Society
    Biochemistry 32 (1993), S. 7323-7328 
    Details
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/bi00080a001
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