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  • 1
    Electronic Resource
    Electronic Resource
    Optically enhanced electron attachment to thiophenol (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 6275-6289 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Enhanced electron attachment to KrF excimer laser irradiated thiophenol (C6H5SH) molecules has been studied in a electron swarm experiment using nitrogen as the buffer gas. Two distinct electron attachment processes were found to be responsible for the observed large enhancement in electron attachment under different experimental conditions. One enhanced electron attachment process occurred immediately (within a few μs) after laser irradiation and is shown to be due to dissociative electron attachment to electronically excited thiophenol molecules in their first excited triplet state produced indirectly via excited singlet states reached by excimer laser irradiation. At low mean electron energies (∼0.1 eV), up to 5 orders of magnitude enhancement in electron attachment has been observed for the triplet state compared to the ground electronic state. This enhanced electron attachment decreased with (i) increasing nitrogen pressure due to quenching of the first excited singlet state of thiophenol (precursor of the triplet state) by nitrogen, and (ii) increasing time delay between laser irradiation and subsequent electron attachment to the laser-irradiated molecules. This latter observation is shown to be due to the self-(triplet–triplet) quenching of the electron attaching triplet state molecules. The second observed enhanced electron attachment process occurred at longer times (〉100 μs) after laser irradiation and is attributed to the electron attachment to diphenyl disulfide (C6H5SSC6H5) produced by the interaction of thiophenoxy radicals (C6H5S (overdot)) formed directly or indirectly via laser irradiation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456344
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  • 2
    Electronic Resource
    Electronic Resource
    Enhanced electron attachment to superexcited states of saturated tertiary amines (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 274-287 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Electron attachment measurements on excimer–laser-excited superexcited states (SES) of saturated amine compounds, and in particular on triethylamine (TEA), have been carried out employing a new experimental technique. A rate equation analysis based on a proposed model shows that the electron attachment rate constant for the SES is several orders of magnitude larger than that for the ground electronic state. The proposed mechanism for electron attachment to SES involves the capture of a near-zero-energy electron—(produced by the same laser pulse that produces the SES)—by a superexcited molecule to form a transient parent anion which subsequently dissociates producing a stable fragment anion. The similarity of the above mechanism to an electron-excited Feshbach resonance is indicated and a scheme for the identification of molecular systems that can be excited (via resonance-enhanced multiphoton excitation) to SES is outlined.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461484
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  • 3
    Electronic Resource
    Electronic Resource
    Spatio-temporal dynamics of the resonantly excited relativistic plasma wave driven by a CO2 laser (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 1434-1447 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The dynamics of a relativistic plasma wave (RPW) resonantly excited by a two frequency CO2 laser pulse and the effects of this wave on a co-propagating relativistic electron beam were studied through experiments and supporting simulations. The amplitude of the RPW and its harmonics were resolved in time and space with a Thomson scattering diagnostic. In addition, the plasma wave amplitude-length product and temporal duration were independently measured through time and frequency resolved forward scattering. The transverse electric and magnetic fields associated with the RPW were studied by the scattering of a 2 MeV electron beam, and the eventual heating of the plasma after the breakup of the RPW was measured from the x-ray radiation spectrum. The experiments and simulations show that the RPW reaches a peak amplitude of approximately 30%, with the amplitude limited by plasma blowout driven by the radial ponderomotive forces of the plasma wave. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872318
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  • 4
    Electronic Resource
    Electronic Resource
    Acceleration and scattering of injected electrons in plasma beat wave accelerator experimentsf| (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 1753-1760 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The results from experiments in which a two-frequency CO2 laser is used to beat-excite large-amplitude, relativistic electron plasma waves in a tunnel-ionized plasma are reported. The plasma wave is diagnosed by injecting a beam of 2 MeV electrons and observing the energy gain and loss of these electrons, as well as the scattering and deflection of the transmitted electrons near 2 MeV. Accelerated electrons up to 30 MeV have been observed. The lifetime of the accelerating structure as seen by small-angle Thomson scattering is about 100 ps, whereas the injected electrons are seen to be scattered or deflected by the plasma for several ns, with diffuse scattering occurring 0.5–1 ns after forming the plasma wave and whole beam deflection occurring at later times. A simple model, which includes laser focusing, ionization, transit time, and relativistic saturation effects, suggests that the wave coherence may be short lived while the wave fields themselves persist for a longer time. This may be the reason for the disparate time scales between the Thomson scattering and the electron scattering diagnostic. The whole beam deflection may be evidence for a Weibel-like instability at later times.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870679
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  • 5
    Electronic Resource
    Electronic Resource
    Coupling between electron plasma waves in laser–plasma interactions (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 2041-2046 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A Lagrangian fluid model (cold plasma, fixed ions) is developed for analyzing the coupling between electron plasma waves. This model shows that a small wave number electron plasma wave (ω2,k2) will strongly affect a large wave number electron plasma wave (ω1,k1), transferring its energy into daughter waves or sidebands at (ω1+nω2,k1+nk2) in the lab frame. The accuracy of the model is checked via particle-in-cell simulations, which confirm that the energy in the mode at (ω1,k1) can be completely transferred to the sidebands at (ω1+nω2,k1+nk2) by the presence of the electron plasma mode at (ω2,k2). Conclusive experimental evidence for the generation of daughter waves via this coupling is then presented using time- and wave number-resolved spectra of the light from a probe laser coherently Thomson scattered by the electron plasma waves generated by the interaction of a two-frequency CO2 laser with a plasma. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871678
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  • 6
    Electronic Resource
    Electronic Resource
    Dissociation of benzene in a pulsed glow discharge (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 3550-3557 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Destruction of benzene in a benzene/Ar mixture subjected to a pulsed glow discharge was studied. The destruction efficiency was much improved compared to a dc glow discharge, and the destruction efficiency increased with decreasing pulse width at a constant pulse frequency. Diagnostics experiments were conducted to elucidate the destruction mechanisms involved. The results show that excitation transfer from the metastable states of Ar to benzene in the afterglow of the discharge was primarily responsible for the destruction of benzene. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.371257
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  • 7
    Electronic Resource
    Electronic Resource
    Two-dimensional Cherenkov emission array for studies of relativistic electron dynamics in a laser plasma : Proceedings of the eleventh topical conference on high temperature plasma diagnostics (1997)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 358-360 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: In laser-produced plasmas there are several effects which will scatter a longitudinally probing relativistic electron beam. In vacuum, the laser itself will ponderomotively defocus the electron beam, while in plasma the ponderomotive force can dig an ion channel which would focus the electron beam. In the cases of plasma wave excitation via the beat-wave or wake-field mechanisms, the thermalization of the electron distribution function can lead to large scale magnetic fields via the Weibel instability. One way of studying such phenomena is to time resolve the transverse current distribution of the electron beam after it exits the plasma. A wire mesh has insufficient time resolution for this purpose, so we instead use a mesh of optical fibers. When the electron beam strikes the fiber mesh, Cherenkov radiation is generated within whichever fibers have current running across them. The Cherenkov radiation from all the fibers can then be analyzed on a streak camera. This allows the reconstruction of j(x,y,t) where j is the current density. We have successfully implemented this technique in the study of beat-excited laser plasmas. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147829
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  • 8
    Electronic Resource
    Electronic Resource
    Enhanced electron attachment to highly excited molecules using a plasma mixing scheme (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 71 (1997), S. 3634-3636 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present preliminary results on a glow discharge-based technique to populate highly excited states of molecules using a novel excitation transfer process, and to efficiently produce negative ions via electron attachment to those excited states. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.120464
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  • 9
    Electronic Resource
    Electronic Resource
    Electron attachment to boron trichloride (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 84 (1998), S. 5805-5807 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Low-energy electron attachment to BCl3 was measured using an electron swarm technique. The parent negative ion, BCl3−, was observed within a narrow electron range close to thermal energy. Previous negative ion measurements in BCl3 discharges, which yielded seemingly inconsistent results, can be shown to be self-consistent based on the present observations. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.368846
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  • 10
    Electronic Resource
    Electronic Resource
    Enhanced formation of negative ions by electron attachment to highly excited molecules in a flowing afterglow plasma (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 84 (1998), S. 3051-3058 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Preliminary evidence for efficient negative-ion formation using a plasma mixing scheme was reported in a recent letter [L. A. Pinnaduwage, W. Ding, and D. L. McCorkle, Appl. Phys. Lett. 71, 3634 (1997)]. In the present article we confirm the negative ion formation using a probe-assisted photodetachment technique and estimate rate constants for electron attachment to electronically excited CH4 and NO in a flowing afterglow plasma. It is shown that enhanced electron attachment to molecules in highly excited states populated via excitation transfer from rare gas metastables is responsible for the observed negative ion formation. Implications for plasma processing and plasma remediation discharges are also discussed. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.368459
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