Physical Review A

Quenching of metastable He+ 2s ions by molecules

Govind P. Gupta, K. C. Mathur

Published May 1, 1981• 3 citations

Abstract

A time-dependent perturbation theory is used to obtain the cross sections and rates for the quenching of metastable helium ions in collision with molecules (${\mathrm{H}}_{2}$, ${\mathrm{N}}_{2}$, ${\mathrm{O}}_{2}$, and C${\mathrm{O}}_{2}$). The results are compared with the recent experimental data of Prior and Wang.

DOI: 10.1103/physreva.23.2347

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Physical Review A

Quenching of metastable He+ 2s ions by molecules

Govind P. Gupta, K. C. Mathur

Published May 1, 1981• 3 citations

Publisher

Abstract

A time-dependent perturbation theory is used to obtain the cross sections and rates for the quenching of metastable helium ions in collision with molecules (

{\mathrm{H}}_{2}

{\mathrm{N}}_{2}

{\mathrm{O}}_{2}

, and C

{\mathrm{O}}_{2}

). The results are compared with the recent experimental data of Prior and Wang.

DOI: 10.1103/physreva.23.2347

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B. Ketzer, F. J. Hartmann, Till von Egidy +13 more

Laser resonance transitions between normally metastable states of antiprotonic helium atoms were induced making use of state dependent quenching effects caused by trace admixtures of H2 to the target helium gas. With this method of “H2-assisted inverse resonances” the decay rates of the states (n,l)=(39,l),l=36,37,38, and (38,l),l=35,36,37 of p̄He+ were determined as a function of the H2 admixture. The quenching cross sections at 30 K deduced therefrom for the states with n=39 were found to be of the order of the geometrical cross section for p̄He+–H2 collisons (2⋅10−15 cm2), with a moderate decrease with increasing l. Within a given cascade with constant v=n−l−1, the quenching cross sections for states with n=38 are smaller by a factor of 4–6 than those for states with n=39.Laser resonance transitions between normally metastable states of antiprotonic helium atoms were induced making use of state dependent quenching effects caused by trace admixtures of H2 to the target helium gas. With this method of “H2-assisted inverse resonances” the decay rates of the states (n,l)=(39,l),l=36,37,38, and (38,l),l=35,36,37 of p̄He+ were determined as a function of the H2 admixture. The quenching cross sections at 30 K deduced therefrom for the states with n=39 were found to be of the order of the geometrical cross section for p̄He+–H2 collisons (2⋅10−15 cm2), with a moderate decrease with increasing l. Within a given cascade with constant v=n−l−1, the quenching cross sections for states with n=38 are smaller by a factor of 4–6 than those for states with n=39.

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The cross sections and rates for quenching of thermalized antiprotonic helium atoms in binary collisions with ordinary helium atoms are calculated in perturbation theory and in the coupled-channel formalism at the temperature and the number density of the helium gas, $T=6\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and $N={10}^{21}\phantom{\rule{0.3em}{0ex}}{\text{cm}}^{\ensuremath{-}3}$, respectively. It is shown that quenching is unlikely to be relevant for the metastable states of the antiprotonic helium atom with $32\ensuremath{\leqslant}n\ensuremath{\leqslant}40$. Comparison with experiment shows a good quantitative agreement for the $(n,l)=(39,35)$ state of antiprotonic helium and a large disagreement for the $(37,34)$ state. As a byproduct of this work, the existence of a series of bound states of the $\mathrm{He}--\overline{p}\phantom{\rule{0.2em}{0ex}}^{4}\mathrm{He}^{+}$ dimer is demonstrated numerically for $n\ensuremath{\geqslant}38$.The cross sections and rates for quenching of thermalized antiprotonic helium atoms in binary collisions with ordinary helium atoms are calculated in perturbation theory and in the coupled-channel formalism at the temperature and the number density of the helium gas, $T=6\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and $N={10}^{21}\phantom{\rule{0.3em}{0ex}}{\text{cm}}^{\ensuremath{-}3}$, respectively. It is shown that quenching is unlikely to be relevant for the metastable states of the antiprotonic helium atom with $32\ensuremath{\leqslant}n\ensuremath{\leqslant}40$. Comparison with experiment shows a good quantitative agreement for the $(n,l)=(39,35)$ state of antiprotonic helium and a large disagreement for the $(37,34)$ state. As a byproduct of this work, the existence of a series of bound states of the $\mathrm{He}--\overline{p}\phantom{\rule{0.2em}{0ex}}^{4}\mathrm{He}^{+}$ dimer is demonstrated numerically for $n\ensuremath{\geqslant}38$.

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Joel I. Gersten

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Quenching of the Heμ + (2s) atom

James Earl Russell

Quenching of the metastable 2s state of the ${\mathrm{He}}_{\mathrm{\ensuremath{\mu}}}$ ${\mathrm{}}^{+}$ atom in helium gas is discussed. The first part of the discussion, which is devoted entirely to processes occurring after the ${\mathrm{He}}_{\mathrm{\ensuremath{\mu}}}$ ${\mathrm{}}^{+}$ has become bound to one or more ordinary helium atoms, is based partly on Cohen's calculations of rates of vibrational quenching and partly on estimates obtained in the present paper of rates of Burbidge--de Borde quenching and Ruderman quenching. It is concluded that Burbidge--de Borde quenching or Ruderman quenching, or both, are likely to be more effective than Cohen quenching if the vibrational level of the bound system is low. A recent experiment by von Arb et al. is then analyzed in the light of this conclusion. The analysis is based on the reported absence, or near absence, of Auger electrons accompanying 2s quenching. While it is agreed that the Cohen mechanism occurring in the molecular ion ${\mathrm{HeHe}}_{\mathrm{\ensuremath{\mu}}}$ ${\mathrm{}}^{+}$ remains the most likely explanation of the experiment, it is concluded that the quenching occurs in comparatively high levels. It is then argued that this conclusion is in accord with some theoretical investigations of three-body association reactions and also with some elementary considerations regarding the relaxation of highly excited diatomic molecules, and it is further concluded that the quenching is most likely to occur in states with very low rotational quantum number and vibrational quantum number 8\ensuremath{\le}v\ensuremath{\le}14.Quenching of the metastable 2s state of the ${\mathrm{He}}_{\mathrm{\ensuremath{\mu}}}$${\mathrm{}}^{+}$ atom in helium gas is discussed. The first part of the discussion, which is devoted entirely to processes occurring after the ${\mathrm{He}}_{\mathrm{\ensuremath{\mu}}}$${\mathrm{}}^{+}$ has become bound to one or more ordinary helium atoms, is based partly on Cohen's calculations of rates of vibrational quenching and partly on estimates obtained in the present paper of rates of Burbidge--de Borde quenching and Ruderman quenching. It is concluded that Burbidge--de Borde quenching or Ruderman quenching, or both, are likely to be more effective than Cohen quenching if the vibrational level of the bound system is low. A recent experiment by von Arb et al. is then analyzed in the light of this conclusion. The analysis is based on the reported absence, or near absence, of Auger electrons accompanying 2s quenching. While it is agreed that the Cohen mechanism occurring in the molecular ion ${\mathrm{HeHe}}_{\mathrm{\ensuremath{\mu}}}$${\mathrm{}}^{+}$ remains the most likely explanation of the experiment, it is concluded that the quenching occurs in comparatively high levels. It is then argued that this conclusion is in accord with some theoretical investigations of three-body association reactions and also with some elementary considerations regarding the relaxation of highly excited diatomic molecules, and it is further concluded that the quenching is most likely to occur in states with very low rotational quantum number and vibrational quantum number 8\ensuremath{\le}v\ensuremath{\le}14.

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Martina Zámečníková, Lucie D. Augustovičová, Wolfgang P Kraemer +1 more

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Stark quenching of metastable 2S states in hydrogen and helium at high fields

Helen K. Holt

The time-dependent theory of the Stark quenching of $2S$ states in hydrogen and helium is developed for high electric fields, fields for which the Stark matrix element is large compared to the state separations. The metastable $2S$ state of an atom is mixed with two $P$ states by the field, and the subsequent decay is described.The time-dependent theory of the Stark quenching of $2S$ states in hydrogen and helium is developed for high electric fields, fields for which the Stark matrix element is large compared to the state separations. The metastable $2S$ state of an atom is mixed with two $P$ states by the field, and the subsequent decay is described.

Physical Review AAug 1, 19830 citations

A time-dependent perturbation theory is used to obtain the cross sections and rates for the quenching of metastable helium ions in collision with molecules (

{\mathrm{H}}_{2}

{\mathrm{N}}_{2}

{\mathrm{O}}_{2}

, and C

{\mathrm{O}}_{2}

). The results are compared with the recent experimental data of Prior and Wang.

T=6\phantom{\rule{0.3em}{0ex}}\mathrm{K}

and $N={10}^{21}\phantom{\rule{0.3em}{0ex}}{\text{cm}}^{\ensuremath{-}3}$, respectively. It is shown that quenching is unlikely to be relevant for the metastable states of the antiprotonic helium atom with $32\ensuremath{\leqslant}n\ensuremath{\leqslant}40$. Comparison with experiment shows a good quantitative agreement for the

(n,l)=(39,35)

state of antiprotonic helium and a large disagreement for the

(37,34)

state. As a byproduct of this work, the existence of a series of bound states of the

\mathrm{He}--\overline{p}\phantom{\rule{0.2em}{0ex}}^{4}\mathrm{He}^{+}

dimer is demonstrated numerically for $n\ensuremath{\geqslant}38$.

Quenching of the metastable 2s state of the ${\mathrm{He}}_{\mathrm{\ensuremath{\mu}}}$

{\mathrm{}}^{+}

atom in helium gas is discussed. The first part of the discussion, which is devoted entirely to processes occurring after the ${\mathrm{He}}_{\mathrm{\ensuremath{\mu}}}$

{\mathrm{}}^{+}

has become bound to one or more ordinary helium atoms, is based partly on Cohen's calculations of rates of vibrational quenching and partly on estimates obtained in the present paper of rates of Burbidge--de Borde quenching and Ruderman quenching. It is concluded that Burbidge--de Borde quenching or Ruderman quenching, or both, are likely to be more effective than Cohen quenching if the vibrational level of the bound system is low. A recent experiment by von Arb et al. is then analyzed in the light of this conclusion. The analysis is based on the reported absence, or near absence, of Auger electrons accompanying 2s quenching. While it is agreed that the Cohen mechanism occurring in the molecular ion ${\mathrm{HeHe}}_{\mathrm{\ensuremath{\mu}}}$

{\mathrm{}}^{+}

remains the most likely explanation of the experiment, it is concluded that the quenching occurs in comparatively high levels. It is then argued that this conclusion is in accord with some theoretical investigations of three-body association reactions and also with some elementary considerations regarding the relaxation of highly excited diatomic molecules, and it is further concluded that the quenching is most likely to occur in states with very low rotational quantum number and vibrational quantum number 8\ensuremath{\le}v\ensuremath{\le}14.

The time-dependent theory of the Stark quenching of

2S

states in hydrogen and helium is developed for high electric fields, fields for which the Stark matrix element is large compared to the state separations. The metastable

2S

state of an atom is mixed with two

P

states by the field, and the subsequent decay is described.