Excitation of the 3p 3Πu level of H2 by electron impact; pressure effects

Baltayan, P.; Nedelec, O.

doi:10.1016/0022-4073(76)90102-3

Cited by 15 publications

(8 citation statements)

References 27 publications

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“…The values labeled with an asterisk for v ′ = 3 − 6 were obtained by extrapolating the lifetimes with the help of a third order polynomial fit of the data from [5] and a constant factor obtained from the average value of the ratios with our values for v ′ = 0 − 2. 6 The dependences of d 3 Π − u , v ′ , N ′ ← X 1 Σ + g ,0,N electron impact excitation on the incident electron energy have been studied in [32,39,40]. They have a normal form for singlet-triplet transitions: a sharp increase from the threshold to the maximum and a rather sharp decrease for higher energies.…”

Section: Constants Of Elementary Processesmentioning

confidence: 99%

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uv continuum emission and diagnostics of hydrogen-containing nonequilibrium plasmas

Lavrov

Melnikov

Käning³

et al. 1999

Phys. Rev. E

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For the first time the emission of the radiative dissociation continuum of the hydrogen molecule (a 3 Σ + g → b 3 Σ + u electronic transition) is proposed to be used as a source of information for the spectroscopic diagnostics of non-equilibrium plasmas. The detailed analysis of excitation-deactivation kinetics, rate constants of various collisional and radiative transitions and fitting procedures made it possible to develop two new methods of diagnostics of: (1) the ground X 1 Σ + g state vibrational temperature T vib from the relative intensity distribution, and (2) the rate of electron impact dissociation (d[H 2 ]/dt) diss from the absolute intensity of the continuum. The known method of determination of T vib from relative intensities of Fulcher-α bands was seriously corrected and simplified due to the revision of d → a transition probabilities and cross sections of d ← X electron impact excitation. General considerations are illustrated with examples of experiments in pure hydrogen capillary-arc and H 2 +Ar microwave discharges. In pure H 2 plasma the values of T vib obtained by two independent methods are in rather good accordance (T vib =3000-5000 K). In the H 2 +Ar microwave plasma it was observed for the first time that the shape of the continuum depends on the ratio of the mixture components. Absorption measurements of the population of the 3s 2 3p 5 4s levels of Ar together with certain computer simulations showed that the Ar*→H 2 excitation transfer plays a significant role. In our typical conditions (power flux: 4 W cm −2 , pressure p = 0.5 mbar, H 2 :Ar=1:1) the following values were obtained for the microwave discharge: (d[H 2 ]/dt) diss ≈ 2.5 − 5 · 10 17 cm −3 s −1 . The contribution of the excitation transfer is about 10-30% of the total population of the a 3 Σ + g state.

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Section: Constants Of Elementary Processesmentioning

confidence: 99%

“…,N electron impact excitation on the incident electron energy have been studied in [32,39,40]. They have a normal form for singlet-triplet transitions: a sharp increase from the threshold to the maximum and a rather sharp decrease for higher energies.…”

mentioning

confidence: 99%

uv continuum emission and diagnostics of hydrogen-containing nonequilibrium plasmas

Lavrov

Melnikov

Käning³

et al. 1999

Phys. Rev. E

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“…58 The cross sections for reaction ͑16͒ with the excitation of molecular hydrogen from the ground H 2 ͑X 1 ⌺ g ϩ ͒ to radiative state H 2 ͑d 3 ⌸ u ͒ are also known both from the theoretical calculations, 59 and from the direct experiments. 60,61 In the interpretation of this experiment we used the most reliable, from our point of view, experimental excitation cross section of Möhlmann and de Heer, 61 with a maximum value about 4.2ϫ10 Ϫ22 m 2 at electron energy of 15.6 eV, which is close to the threshold of excitation.…”

Section: B Kinetic Of Hydrogen Excited Statesmentioning

confidence: 99%

“…Analysis of the experimental and theoretical data on electron impact excitation of atomic and molecular radiative states H*͑pϭ3,4,5͒ and H 2 ͑d 3 ⌸ u ͒ [51][52][53][54][55][56][57][58][59][60][61] show that the cross sections have similar shapes: a sharp rise near the thresholds, and a slow decrease for higher electron energies. Therefore, the ratio between the corresponding excitation cross sections can be used for the ratio between the rate constants of the direct electron excitation of H* and H 2 * as a first approximation.…”

Section: ϫ3mentioning

confidence: 99%

Diagnostics of the magnetized low-pressure hydrogen plasma jet: Molecular regime

Qing

Otorbaev

Brussaard

et al. 1996

Journal of Applied Physics

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Optical emission and absorption spectroscopy and double Langmuir probe diagnostics have been applied to measure the plasma parameters of an expanding magnetized hydrogen plasma jet. The rotational temperature of the excited state H 2 ͑d 2 ⌸ u ) has been determined by analyzing the intensity distribution of the spectral lines of the Fulcher-␣ system of H 2 . The gas temperature in the plasma, which is twice the value of the rotational temperature is equal to Ӎ 520 K. Several clear indications of presence of the ''hot'' electrons have been observed in the plasma: ͑1͒ Langmuir probe measurements ͑T e Ӎ1.4 eV͒, ͑2͒ appearance of the Fulcher-␣ system of H 2 ͑excitation potential ⌬Eϭ13.87 eV͒, ͑3͒ low rotational temperature ͑T rot * Ӎ260 K͒ of the excited H 2 ͑d 3 ⌸ u ) molecules, ͑4͒ local excitation in the plasma of Ar I͑⌬E ϭ15.45 eV͒, and Ar II͑⌬E ϭ19.68 eV͒ spectral lines, ͑5͒ local excitation in the plasma of He I͑⌬E ϭ23.07 eV and ⌬Eϭ24.04 eV͒ spectral lines. Optical actinometry has been applied to measure the absolute density of hydrogen atoms and hydrogen dissociation degree in the plasma. The measured absolute density of hydrogen atoms are in the ͑1-1.4͒ϫ10 20 m Ϫ3 range, and the corresponding dissociation degree of the hydrogen plasma is in the range of 8%-13%.

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“…Cross sections of the excitation of the Fulcher-α system have been experimentally studied in a number of works [25][26][27][28]. The excitation function, i.e.…”

Section: Excitation Of the Fulcher-α (2-2)q1 Line Of Molecular Hydrogenmentioning

confidence: 99%

On determination of the degree of dissociation of hydrogen in non-equilibrium plasmas by means of emission spectroscopy: I. The collision-radiative model and numerical experiments

Lavrov¹,

Pipa²,

Röpcke³

2006

Plasma Sources Sci. Technol.

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A new spectroscopic method of determination of the degree of dissociation of hydrogen is proposed. The method is based on measurements of the relative intensities of two atomic lines of the Balmer series, H α and H β , and of one molecular line, the (2-2)Q1 line of the Fulcher-α system. These intensities are related to two plasma parameters: (i) the ratio of atomic and molecular hydrogen densities [H]/[H 2 ], connected with the degree of dissociation of hydrogen and (ii) the artificial parameter T eff e , characterizing a tail of an electron energy distribution function (EEDF) in the threshold region of electron impact excitation cross sections. The link between measured relative line intensities and plasma parameters was found in the framework of a most simple collision-radiative model taking into account only the direct and dissociative electron impact excitation and spontaneous decay of excited states. Numerical simulations made it possible to analyse main peculiarities and to estimate the range of the applicability of the method concerning numerical values of [H]/[H 2 ] and T eff e . For the first time, the fine structure of Balmer lines was taken into account in the spectroscopic determination of the degree of dissociation of hydrogen in non-equilibrium plasmas. The rate coefficients for electron impact excitation of the d 3 − u , v = 2, N = 1 rovibronic level of the hydrogen molecule were calculated with a Maxwellian EEDF for electron temperatures T e = 0.5-100 eV. Earlier calculated values of the emission rate coefficients for direct and dissociative electron impact excitation of H α and H β lines were extended for electron temperatures up to 100 eV.

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Excitation of the 3p 3Πu level of H2 by electron impact; pressure effects

Cited by 15 publications

References 27 publications

uv continuum emission and diagnostics of hydrogen-containing nonequilibrium plasmas

uv continuum emission and diagnostics of hydrogen-containing nonequilibrium plasmas

Diagnostics of the magnetized low-pressure hydrogen plasma jet: Molecular regime

On determination of the degree of dissociation of hydrogen in non-equilibrium plasmas by means of emission spectroscopy: I. The collision-radiative model and numerical experiments

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