Physical Review Letters

Quenching of Metastable Hydrogen by Helium

Robert S. Kass, W. Williams

Published Aug 23, 1971• 13 citations

Abstract

Measurements of collisional quenching of metastable hydrogen by helium in the thermal region ($v\ensuremath{\simeq}5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$ a.u.) have been made. The resulting cross section ${\ensuremath{\sigma}}_{Q}\ensuremath{\simeq}8\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}15}$ ${\mathrm{cm}}^{2}$ per atom is 20-25% larger than the theoretical results obtained by Byron and Gersten using a pseudopotential method.

DOI: 10.1103/physrevlett.27.473

Related papers

Collisional quenching of antiprotonic helium atoms in gaseous helium

Boyan Obreshkov, D. Bakalov, Bruno Lepetit +1 more

Physical Review AApr 1, 200417 citations

Temperature Dependence of Helium Metastability Exchange Cross Section

F. D. Colegrove, L. D. Schearer, G. K. Walters

Physical ReviewJul 20, 196451 citations

Quenching of metastable states of antiprotonic helium atoms by collisions with H2 molecules

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

The Journal of Chemical PhysicsJul 8, 199817 citations

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

Helen K. Holt

Physical Review AAug 1, 19830 citations

Scattering of H¯(1s) off metastable helium atom at thermal energies

Prabal K. Sinha, Arnab Ghosh

Physical Review AJun 12, 20062 citations

Hydrogen-Assisted Laser-Induced Resonant Transitions between Metastable States of Antiprotonic Helium Atoms

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

Physical Review LettersMar 3, 199735 citations

Physical Review Letters

Quenching of Metastable Hydrogen by Helium

Robert S. Kass, W. Williams

Published Aug 23, 1971• 13 citations

Publisher

Abstract

Measurements of collisional quenching of metastable hydrogen by helium in the thermal region (

v\ensuremath{\simeq}5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}

a.u.) have been made. The resulting cross section

{\ensuremath{\sigma}}_{Q}\ensuremath{\simeq}8\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}15}

{\mathrm{cm}}^{2}

per atom is 20-25% larger than the theoretical results obtained by Byron and Gersten using a pseudopotential method.

DOI: 10.1103/physrevlett.27.473

Related papers

Collisional quenching of antiprotonic helium atoms in gaseous helium

Boyan Obreshkov, D. Bakalov, Bruno Lepetit +1 more

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 $n\ensuremath{\geqslant}38$.

Physical Review AApr 1, 200417 citations

Temperature Dependence of Helium Metastability Exchange Cross Section

F. D. Colegrove, L. D. Schearer, G. K. Walters

The cross section for exchange of metastability in collisions between ${\mathrm{He}}^{3}$ atoms in the ground ( $1^{1}S_{0}$ ) state and metastable ( $2^{3}S_{1}$ ) state has been measured as a function of temperature by optical pumping techniques. The exchange cross section decreases from about 5.5\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}16}$ ${\mathrm{cm}}^{2}$ at 500\ifmmode^\circ\else\textdegree\fi{}K to less than ${10}^{\ensuremath{-}17}$ ${\mathrm{cm}}^{2}$ at 4.2\ifmmode^\circ\else\textdegree\fi{}K. These results suggest a thermally activated exchange process in qualitative agreement with the predicted existence of a long-range repulsive interaction between metastable and ground-state helium atoms as proposed by Buckingham and Dalgarno.The cross section for exchange of metastability in collisions between ${\mathrm{He}}^{3}$ atoms in the ground ($1^{1}S_{0}$) state and metastable ($2^{3}S_{1}$) state has been measured as a function of temperature by optical pumping techniques. The exchange cross section decreases from about 5.5\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}16}$ ${\mathrm{cm}}^{2}$ at 500\ifmmode^\circ\else\textdegree\fi{}K to less than ${10}^{\ensuremath{-}17}$ ${\mathrm{cm}}^{2}$ at 4.2\ifmmode^\circ\else\textdegree\fi{}K. These results suggest a thermally activated exchange process in qualitative agreement with the predicted existence of a long-range repulsive interaction between metastable and ground-state helium atoms as proposed by Buckingham and Dalgarno.

Physical ReviewJul 20, 196451 citations

Quenching of metastable states of antiprotonic helium atoms by collisions with H2 molecules

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.

The Journal of Chemical PhysicsJul 8, 199817 citations

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

Scattering of H¯(1s) off metastable helium atom at thermal energies

Prabal K. Sinha, Arnab Ghosh

Quantal calculations for scattering of ground-state antihydrogen by metastable $(n=2S)$ helium atoms have been performed using the nonadiabatic, atomic orbital expansion technique at thermal energies. The zero-energy elastic cross sections of the present systems are much greater than the corresponding value for the ground-state helium target. The low-energy elastic cross section for the singlet metastable helium $[\mathrm{He}(2\phantom{\rule{0.2em}{0ex}}^{1}S)]$ target is higher than the corresponding value when the target is in the metastable triplet state $[\mathrm{He}(2\phantom{\rule{0.2em}{0ex}}^{3}S)]$ .Quantal calculations for scattering of ground-state antihydrogen by metastable $(n=2S)$ helium atoms have been performed using the nonadiabatic, atomic orbital expansion technique at thermal energies. The zero-energy elastic cross sections of the present systems are much greater than the corresponding value for the ground-state helium target. The low-energy elastic cross section for the singlet metastable helium $[\mathrm{He}(2\phantom{\rule{0.2em}{0ex}}^{1}S)]$ target is higher than the corresponding value when the target is in the metastable triplet state $[\mathrm{He}(2\phantom{\rule{0.2em}{0ex}}^{3}S)]$.

Physical Review AJun 12, 20062 citations

Hydrogen-Assisted Laser-Induced Resonant Transitions between Metastable States of Antiprotonic Helium Atoms

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

Laser resonance transitions between normally metastable states of antiprotonic helium atoms were observed making use of state dependent quenching effects caused by small admixtures of ${\mathrm{H}}_{2}$ molecules. By selectively shortening the lifetimes of states with higher principal quantum number $n$ as compared to those of lower $n$ , this method for the first time provides access to all initially populated metastable states of $\overline{p}{\mathrm{He}}^{+}$ atoms. This was demonstrated by observing the transitions $(n,l)\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}(38,l)\ensuremath{\rightarrow}(39,l+1)$, $l\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}35,36,37$ and $(n,l)\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}(37,l)\ensuremath{\rightarrow}(38,l+1)$, $l\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}34,35,36$ .Laser resonance transitions between normally metastable states of antiprotonic helium atoms were observed making use of state dependent quenching effects caused by small admixtures of ${\mathrm{H}}_{2}$ molecules. By selectively shortening the lifetimes of states with higher principal quantum number $n$ as compared to those of lower $n$, this method for the first time provides access to all initially populated metastable states of $\overline{p}{\mathrm{He}}^{+}$ atoms. This was demonstrated by observing the transitions $(n,l)\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}(38,l)\ensuremath{\rightarrow}(39,l+1)$, $l\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}35,36,37$ and $(n,l)\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}(37,l)\ensuremath{\rightarrow}(38,l+1)$, $l\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}34,35,36$.

Physical Review LettersMar 3, 199735 citations

Measurements of collisional quenching of metastable hydrogen by helium in the thermal region (

v\ensuremath{\simeq}5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}

a.u.) have been made. The resulting cross section

{\ensuremath{\sigma}}_{Q}\ensuremath{\simeq}8\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}15}

{\mathrm{cm}}^{2}

per atom is 20-25% larger than the theoretical results obtained by Byron and Gersten using a pseudopotential method.

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 section for exchange of metastability in collisions between

{\mathrm{He}}^{3}

atoms in the ground (

1^{1}S_{0}

) state and metastable (

2^{3}S_{1}

) state has been measured as a function of temperature by optical pumping techniques. The exchange cross section decreases from about 5.5\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}16}$

{\mathrm{cm}}^{2}

at 500\ifmmode^\circ\else\textdegree\fi{}K to less than ${10}^{\ensuremath{-}17}$

{\mathrm{cm}}^{2}

at 4.2\ifmmode^\circ\else\textdegree\fi{}K. These results suggest a thermally activated exchange process in qualitative agreement with the predicted existence of a long-range repulsive interaction between metastable and ground-state helium atoms as proposed by Buckingham and Dalgarno.

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.

Quantal calculations for scattering of ground-state antihydrogen by metastable

(n=2S)

helium atoms have been performed using the nonadiabatic, atomic orbital expansion technique at thermal energies. The zero-energy elastic cross sections of the present systems are much greater than the corresponding value for the ground-state helium target. The low-energy elastic cross section for the singlet metastable helium

[\mathrm{He}(2\phantom{\rule{0.2em}{0ex}}^{1}S)]

target is higher than the corresponding value when the target is in the metastable triplet state

[\mathrm{He}(2\phantom{\rule{0.2em}{0ex}}^{3}S)]

Laser resonance transitions between normally metastable states of antiprotonic helium atoms were observed making use of state dependent quenching effects caused by small admixtures of

{\mathrm{H}}_{2}

molecules. By selectively shortening the lifetimes of states with higher principal quantum number

n

as compared to those of lower

n

, this method for the first time provides access to all initially populated metastable states of

\overline{p}{\mathrm{He}}^{+}

atoms. This was demonstrated by observing the transitions $(n,l)\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}(38,l)\ensuremath{\rightarrow}(39,l+1)$,

l\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}35,36,37

and $(n,l)\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}(37,l)\ensuremath{\rightarrow}(38,l+1)$,

l\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}34,35,36