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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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Focuses on a study which reexamined the reactions of helium with argon at atmospheric pressures. Information on effective rate coefficient and destruction frequency; Methodology of the study; Results and discussion.

Intense (up to a few 10(17) W/ cm2) femtosecond (down to 40 fs) laser pulses are focused onto a partially clusterized argon gas jet. The target was previously characterized and optimized in order to get a homogeneous and dense jet of clusters with a well controlled size. The interaction leads to x-ray emission that is absolutely calibrated and spectrally resolved using a high resolution time-integrated spectrometer in the K-shell range (from 2.9 to 4.3 keV). X-ray spectra are investigated as a function of different laser temporal parameters such as the nanosecond prepulse contrast, the laser pulse duration, and the femtosecond delay between two different laser pulses. The cluster size ranges from 180 to 350 angstroms and irradiation by laser pulses with both linear and circular polarization is investigated. The experimental results are discussed in terms of the laser-cluster interaction dynamics. They are compared with the predictions of collision-dominated nanoplasma models. However, further interaction processes are required in order to explain the observed characteristic lines demonstrating highly charged ions up to Ar16+.