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1

Digitale Medien

Study of two-body and three-body channels for the reaction of metastable helium atoms with selected atomic and molecular species (1988)

Pouvesle, J. M. ; Khacef, A. ; Stevefelt, J. ; [weitere]

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 88 (1988), S. 3061-3071

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ISSN: 1089-7690

Quelle: AIP Digital Archive

Thema: Physik , Chemie und Pharmazie

Notizen: This work reports the measurements of rate coefficients for excitation transfer reactions of metastable He(2 3S) atoms, produced in 0.3–4 atm of helium, with various reactants presenting a wide range of characteristics. In all cases studied, three-body reaction channels were identified with most probable values of rate coefficients lying in the range from 0.2 to 6.7×10−31 cm6 s−1, for Ne and N2O, respectively. These are generally more than one order of magnitude smaller than previously reported. The interpretation of this discrepancy in terms of a more reactive intermediate He2(Σ*) complex in dynamic equilibrium with the He(2 3S) population seems to be confirmed, and is analyzed in some detail.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.453949

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2

Digitale Medien

Study of a fast ablative capillary discharge dedicated to soft x-ray production (2000)

Hong, D. ; Dussart, R. ; Cachoncinlle, C. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Review of Scientific Instruments 71 (2000), S. 15-19

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ISSN: 1089-7623

Quelle: AIP Digital Archive

Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik

Notizen: A capillary discharge has been developed to produce pulses of intense soft x-ray radiation of tens of nanoseconds duration. The soft x-ray photons were emitted in a plasma column resulting from polyethylene in capillary wall ablation. The spectrum was dominated by the C IV, C V, and C VI emission lines in the soft x-ray spectral range. The experimental value of the electrical circuit inductance has been measured and compared to the calculated one. The electron temperature was estimated to be higher than 50 eV from the plasma resistivity measurement. The time dependence of the electron density outside the capillary channel has been determined using spectroscopic measurement in the visible range. The time dependence of the electron temperature has been determined from the intensity ratio of C V and C VI emission lines, using a collisional radiative equilibrium code. © 2000 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.1150152

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3

Digitale Medien

Reactivity of metastable helium molecules in atmospheric pressure afterglows (1985)

Pouvesle, J. M. ; Stevefelt, J. ; Lee, F. W. ; [weitere]

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 83 (1985), S. 2836-2839

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ISSN: 1089-7690

Quelle: AIP Digital Archive

Thema: Physik , Chemie und Pharmazie

Notizen: This work focuses upon previously encountered problems that have impeded the understanding of the role of He2(3Σu) metastable molecules in the afterglows of electrical discharges into atmospheric pressures of helium containing admixtures of reactants. New data are reported that generally confirm the literature values for the reactivities of this species at high pressures and continue the disagreement with earlier measurements in low pressure plasmas. Results are presented for reactions with HCl and HBr for the first time. A study of systematic dependencies of rates upon molecular parameters is reported which shows that the ratio for bimolecular reactions of vibrationally excited and unexcited He2(3Σu) molecules is largely independent of the identity of the reacting partner. This provides a means for using data on the pressure dependent part of the effective rate of reaction of He(2 3S) atoms to estimate the rate coefficients for the bimolecular reactions of the more elusive He2(3Σu) molecule.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.449233

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4

Digitale Medien

Spectroscopic study of the afterglow excited by intense electrical discharges in high-pressure helium hydrogen mixtures (1985)

Motret, O. ; Pouvesle, J. M. ; Stevefelt, J.

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 83 (1985), S. 1095-1100

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ISSN: 1089-7690

Quelle: AIP Digital Archive

Thema: Physik , Chemie und Pharmazie

Notizen: In this work, we report the study of afterglow plasmas with initial electron density over 1015 cm−3 excited by repetitive 3 kA, 7 ns duration discharges in He–H2 mixtures with helium pressure in the range 310–760 Torr and partial pressure of hydrogen from 20 to 400 mTorr. The afterglow radiation was emitted in He2 transitions as well as in atomic hydrogen spectral lines, with Lα being particularly intense. The ground state H concentration was estimated from the profile of the self-absorbed Lα line, indicating that dissociation of hydrogen occurs mainly in the afterglow by electron–ion recombination. He (2 3S) destruction frequencies have been determined from measurements of the optical absorption of the 2 3S→3 3P helium transition and were analyzed in terms of rate coefficients for various quenching processes. Among these, the Penning reaction with atomic hydrogen was found to be important.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.449856

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5

Digitale Medien

Reactions of He(2 3S) with argon at atmospheric pressures (1986)

Pouvesle, J. M. ; Viladrosa, R. ; Motret, O. ; [weitere]

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 85 (1986), S. 2338-2340

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ISSN: 1089-7690

Quelle: AIP Digital Archive

Thema: Physik , Chemie und Pharmazie

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.451084

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6

Digitale Medien

Study of two-body and three-body channels for the reaction of metastable helium atoms with nitrogen (1985)

Pouvesle, J. M. ; Stevefelt, J. ; Collins, C. B.

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 82 (1985), S. 2274-2279

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ISSN: 1089-7690

Quelle: AIP Digital Archive

Thema: Physik , Chemie und Pharmazie

Notizen: This work reports the characterization of late time periods in the decay of metastable He(2 3S) atoms produced in 1–4 atm of helium containing up to 1400 mTorr of N2. Results have been obtained that exploit the large dynamic range and high data acquisition rates available from time resolved spectroscopic studies of preionized stripline discharges. A new value was found for the termolecular reaction of (2 3S) with N2 of 1.5×10−31 cm6 s−1 that is in good agreement with a model of collisionally induced capture. An indirect channel of reaction was also found that seems to explain the anomalously rapid and conflicting termolecular rates that were previously reported.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.448322

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7

Digitale Medien

Study of the gamma emission from the 31-yr isomer of 178Hf induced by x-ray irradiation (2000)

Collins, C. B. ; Davanloo, F. ; Iosif, M. C. ; [weitere]

Springer

Physics of atomic nuclei 63 (2000), S. 2067-2072

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ISSN: 1063-7788

Quelle: Springer Online Journal Archives 1860-2000

Thema: Physik

Notizen: Abstract A sample containing 6.3×1014 nuclei of the 16+ isomer of 178Hf having a half-life of 31 yr and an excitation energy of 2.446 MeV was irradiated with x-ray pulses from a device operated at 15 mA to produce bremsstrahlung with an endpoint energy of 90 keV. The gamma spectra of the isomeric target were taken with a Ge detector. The intensity of the 325.5-keV (6+ → 4+) transition in the ground-state band of 178Hf was found to increase by about 2%. Such an enhanced decay of the 178Hf isomer is consistent with an integrated cross section value of 3×10−23 cm2 keV if resonance absorption occurs within energy ranges corresponding to the maxima of the x-ray flux, either near 20 keV or at the energies of the characteristic emission lines of W.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1134/1.1333875

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