Physical Review A

Bound states and decay mechanisms of He−

Cleanthes A. Nicolaides, Yannis Komninos, Donald R. Beck

Published Aug 1, 1981• 84 citations

Abstract

Detailed electron-correlation calculations which include the mixing of closed channel with open channels, suggest that ${\mathrm{He}}^{\ensuremath{-}}$ has only two bound states: The $1s2s2p^{4}P^{o}$ and the $2{p}^{3}^{4}S^{o}$. The $1s2{p}^{2}^{4}P$ and $^{2}P$ states are above the He $1s2p^{3}P^{o}$ threshold and therefore qualify only as core-excited shape resonances. This conclusion contradicts certain previous theoretical and experimental findings which implied the existence of bound ${\mathrm{He}}^{\ensuremath{-}}^{4}P$ and $^{2}P$ states. Both $^{4}P^{o}$ and $^{4}S^{o}$ autoionize to the adjacent continuum via spin-dependent forces---a well-known decay mechanism. However, there are two more decay mechanisms: nonrelativistic (for $^{4}S^{o}$) and relativistic (for $^{4}P^{o}$) radiative autoionization (RA). The probability for RA of the $^{4}S^{o}$ state in the Hartree-Fock approximation is computed to be 1.14\ifmmode\times\else\texttimes\fi{}${10}^{10}$ ${\mathrm{sec}}^{\ensuremath{-}1}$

DOI: 10.1103/physreva.24.1103

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Metastable-ion lifetime studies utilizing a heavy-ion storage ring: Measurements on He−

T. Andersen, L. H. Andersen, Péter Balling +4 more

Physical Review AFeb 1, 199377 citations

2P0resonances in He-

B. R. Junker

Journal of Physics B Atomic and Molecular PhysicsDec 28, 198218 citations

Near-threshold excitation of the λ132.2 nm resonance line of the Tl+ ion by electron impact

Г. М. Гомонай, V Roman, Л. О. Бандуріна +3 more

Scientific Herald of Uzhhorod University Series PhysicsDec 31, 20180 citations

Resonance profiles for electron-ion photorecombination at an isolated resonance

Stanley L. Haan

Physical Review AOct 1, 19895 citations

Bound state properties, positron annihilation and hyperfine structure splittings in the four-body positron-helium $$e^{+} [^{3}$$He($$2^{3}S_e$$)] and $$e^{+} [^{4}$$He($$2^{3}S_e$$)] ions

Alexei M. Frolov

The European Physical Journal DApr 1, 20251 citation

1s2s2pP2 resonance of He−

Kwong T. Chung

Physical Review AMar 1, 198134 citations

Physical Review A

Bound states and decay mechanisms of He−

Cleanthes A. Nicolaides, Yannis Komninos, Donald R. Beck

Published Aug 1, 1981• 84 citations

Publisher

Abstract

Detailed electron-correlation calculations which include the mixing of closed channel with open channels, suggest that

{\mathrm{He}}^{\ensuremath{-}}

has only two bound states: The

1s2s2p^{4}P^{o}

and the

2{p}^{3}^{4}S^{o}

. The

1s2{p}^{2}^{4}P

and

^{2}P

states are above the He

1s2p^{3}P^{o}

threshold and therefore qualify only as core-excited shape resonances. This conclusion contradicts certain previous theoretical and experimental findings which implied the existence of bound

{\mathrm{He}}^{\ensuremath{-}}^{4}P

and

^{2}P

states. Both

^{4}P^{o}

and

^{4}S^{o}

autoionize to the adjacent continuum via spin-dependent forces---a well-known decay mechanism. However, there are two more decay mechanisms: nonrelativistic (for

^{4}S^{o}

) and relativistic (for

^{4}P^{o}

) radiative autoionization (RA). The probability for RA of the

^{4}S^{o}

state in the Hartree-Fock approximation is computed to be 1.14\ifmmode\times\else\texttimes\fi{}

{10}^{10}

{\mathrm{sec}}^{\ensuremath{-}1}

DOI: 10.1103/physreva.24.1103

Related papers

Metastable-ion lifetime studies utilizing a heavy-ion storage ring: Measurements on He−

T. Andersen, L. H. Andersen, Péter Balling +4 more

The lifetime of the metastable autodetaching 1s2s2p $^{4}$ ${\mathit{P}}_{5/2}$ level of the $^{4}\mathrm{He}^{\mathrm{\ensuremath{-}}}$ ion has been measured by a time-of-flight technique to be 350\ifmmode\pm\else\textpm\fi{}15 \ensuremath{\mu}s using a heavy-ion storage ring. Blackbody-induced photodetachment of this weakly bound level is shown to influence the decay rate by nearly 20%, an effect not discussed previously. The magnetic-field-induced mixing effects provide additional information about the lifetime of the close-lying $^{4}$ ${\mathit{P}}_{3/2}$ level, yielding \ensuremath{\tau} ${(}^{4}$ ${\mathit{P}}_{3/2}$ )=12\ifmmode\pm\else\textpm\fi{}2 \ensuremath{\mu}s. The observed lifetimes are consistent with previous experimental values, but the accuracy of the $^{4}$ ${\mathit{P}}_{5/2}$ lifetime is improved by a factor of 6, allowing a detailed test of theoretical predictions to be performed. The $^{4}$ ${\mathit{P}}_{5/2}$ lifetime is significantly shorter than most recent advanced theoretical results, but in agreement with a multiconfiguration Hartree-Fock approach accurately describing the initial bound $^{4}$ ${\mathit{P}}_{5/2}$ and the final continuum $^{2}$ ${\mathit{F}}_{5/2}$ states.The lifetime of the metastable autodetaching 1s2s2p $^{4}$${\mathit{P}}_{5/2}$ level of the $^{4}\mathrm{He}^{\mathrm{\ensuremath{-}}}$ ion has been measured by a time-of-flight technique to be 350\ifmmode\pm\else\textpm\fi{}15 \ensuremath{\mu}s using a heavy-ion storage ring. Blackbody-induced photodetachment of this weakly bound level is shown to influence the decay rate by nearly 20%, an effect not discussed previously. The magnetic-field-induced mixing effects provide additional information about the lifetime of the close-lying $^{4}$${\mathit{P}}_{3/2}$ level, yielding \ensuremath{\tau}${(}^{4}$${\mathit{P}}_{3/2}$)=12\ifmmode\pm\else\textpm\fi{}2 \ensuremath{\mu}s. The observed lifetimes are consistent with previous experimental values, but the accuracy of the $^{4}$${\mathit{P}}_{5/2}$ lifetime is improved by a factor of 6, allowing a detailed test of theoretical predictions to be performed. The $^{4}$${\mathit{P}}_{5/2}$ lifetime is significantly shorter than most recent advanced theoretical results, but in agreement with a multiconfiguration Hartree-Fock approach accurately describing the initial bound $^{4}$${\mathit{P}}_{5/2}$ and the final continuum $^{2}$${\mathit{F}}_{5/2}$ states.

Physical Review AFeb 1, 199377 citations

2P0resonances in He-

B. R. Junker

Reports a number of calculations for the 2 P 0 resonances in He - below the 2 3 P 0 state of He. These calculations indicate that there is no 2 P 0 shape resonance associated with the 2 3 S state of helium that the Feshbach resonance associated with the 2 1 S state of He (as calculated by Chung (1981), and Bhatia and Temkin (1981)) is shifted down to the vicinity of the resonance computed by Burke et al. (1969) and Oberoi and Nesbet (1973), and that there appears to be no second 2 P 0 resonance between the 2 1 S and 2 3 P 0 states of He.Reports a number of calculations for the 2 P 0 resonances in He - below the 2 3 P 0 state of He. These calculations indicate that there is no 2 P 0 shape resonance associated with the 2 3 S state of helium that the Feshbach resonance associated with the 2 1 S state of He (as calculated by Chung (1981), and Bhatia and Temkin (1981)) is shifted down to the vicinity of the resonance computed by Burke et al. (1969) and Oberoi and Nesbet (1973), and that there appears to be no second 2 P 0 resonance between the 2 1 S and 2 3 P 0 states of He.

Journal of Physics B Atomic and Molecular PhysicsDec 28, 198218 citations

Near-threshold excitation of the λ132.2 nm resonance line of the Tl+ ion by electron impact

Г. М. Гомонай, V Roman, Л. О. Бандуріна +3 more

Background : Among all processes of collision of electrons with atomic particles the study of the interaction between electrons and ions is extremely important and necessary for a better understanding of the basic collisional processes in plasma. In the processes of excitation, recombination, and ionization of ions by electron impact autoionization states play an important role. Their radiation decay makes an additional contribution to the photo-recombination process and leads to dielectronic recombination of an ion. Such contribution is most significant in the case of heavy many-electron ions such as the Tl + ion. Excitation of the Tl + ion by an electron impact at electron-ion collisions is practically not investigated up to date. Methods: Experiments were performed using a spectroscopic method in conditions of electron and ion beams intersecting at an angle of 90°. The ribbon electron beam (cross section 1×8 mm 2 , energy E e = 6–14 eV, current I e = (2–10)×10 –5 A) was formed by a low-energy three-electrode electron gun. The ion beam (cross section 2.5×2.5 mm 2 , energy E i = 800 eV, current I i = (5–7)×10 –7 A) was obtained using a low-voltage arc discharge source. The radiation due to decay of the ion states excited during the collisions was detected perpendicular to the plane of the beams intersection. Spectral separation of the radiation in a vacuum ultraviolet region was carried out by 70° vacuum monochromator based on the Seya-Namioka scheme. Results: Thorough measurements of the near-threshold region of the energy dependence of the effective cross section of the electron excitation of the resonance l 132.2 nm line (6 s 6 p 1 P o 1 → 6 s 2 1 S 0 ) of the Tl + ion in the 6–14 eV energy range revealed resonant features both after and before the excitation threshold of the line. The widths of the before-threshold peculiarities is defined by the dispersion of the excited electrons energy. This is indicative of their resonant nature, i.e., they are due to the formation and decay of the atoionization states (AIS) of the Tl atom. Most likely, they are related to the formation and decay of the AIS of the 6 s 6 pnp configuration ( n ≥ 7) to the excited levels of the Tl atom. The nature of the after-threshold structure indicates that it is also the result of resonance processes and is due to the formation and decay of the AIS, most likely of the 5 d 9 6 s 2 6 p 2 configuration, in the electronic channel. The absolute values of the excitation cross sections of the dielectronic satellites were determined by comparison of their intensities with the intensity of the resonance l 132.2 nm line which effective excitation cross section was obtained by normalizing the experimental data on the theoretical calculation by the tight-binding method of two states of the excitation cross section of the 6 s 6 p 1 P o 1 level of the Tl + ion at the 100 eV energy. Conclusions: The energy dependence of the effective excitation cross section of the dielectronic satellites of the Tl + ion resonance line showed that the absolute values of their excitation cross sections are ~ 10 –16 cm 2 and are of the same order of magnitude with that for the resonance line. It is shown that the main excitation mechanism of the resonance line satellites is dielectronic recombination which effectiveness essentially depends on the ratio of the probabilities of the AIS radiation and electron decay. In the case of the relativistic Tl + ion a strong configuration mixing of levels leads to significant increase of the AIS radiation decay probability.Background : Among all processes of collision of electrons with atomic particles the study of the interaction between electrons and ions is extremely important and necessary for a better understanding of the basic collisional processes in plasma. In the processes of excitation, recombination, and ionization of ions by electron impact autoionization states play an important role. Their radiation decay makes an additional contribution to the photo-recombination process and leads to dielectronic recombination of an ion. Such contribution is most significant in the case of heavy many-electron ions such as the Tl + ion. Excitation of the Tl + ion by an electron impact at electron-ion collisions is practically not investigated up to date. Methods: Experiments were performed using a spectroscopic method in conditions of electron and ion beams intersecting at an angle of 90°. The ribbon electron beam (cross section 1×8 mm 2 , energy E e = 6–14 eV, current I e = (2–10)×10 –5 A) was formed by a low-energy three-electrode electron gun. The ion beam (cross section 2.5×2.5 mm 2 , energy E i = 800 eV, current I i = (5–7)×10 –7 A) was obtained using a low-voltage arc discharge source. The radiation due to decay of the ion states excited during the collisions was detected perpendicular to the plane of the beams intersection. Spectral separation of the radiation in a vacuum ultraviolet region was carried out by 70° vacuum monochromator based on the Seya-Namioka scheme. Results: Thorough measurements of the near-threshold region of the energy dependence of the effective cross section of the electron excitation of the resonance l 132.2 nm line (6 s 6 p 1 P o 1 → 6 s 2 1 S 0 ) of the Tl + ion in the 6–14 eV energy range revealed resonant features both after and before the excitation threshold of the line. The widths of the before-threshold peculiarities is defined by the dispersion of the excited electrons energy. This is indicative of their resonant nature, i.e., they are due to the formation and decay of the atoionization states (AIS) of the Tl atom. Most likely, they are related to the formation and decay of the AIS of the 6 s 6 pnp configuration ( n ≥ 7) to the excited levels of the Tl atom. The nature of the after-threshold structure indicates that it is also the result of resonance processes and is due to the formation and decay of the AIS, most likely of the 5 d 9 6 s 2 6 p 2 configuration, in the electronic channel. The absolute values of the excitation cross sections of the dielectronic satellites were determined by comparison of their intensities with the intensity of the resonance l 132.2 nm line which effective excitation cross section was obtained by normalizing the experimental data on the theoretical calculation by the tight-binding method of two states of the excitation cross section of the 6 s 6 p 1 P o 1 level of the Tl + ion at the 100 eV energy. Conclusions: The energy dependence of the effective excitation cross section of the dielectronic satellites of the Tl + ion resonance line showed that the absolute values of their excitation cross sections are ~ 10 –16 cm 2 and are of the same order of magnitude with that for the resonance line. It is shown that the main excitation mechanism of the resonance line satellites is dielectronic recombination which effectiveness essentially depends on the ratio of the probabilities of the AIS radiation and electron decay. In the case of the relativistic Tl + ion a strong configuration mixing of levels leads to significant increase of the AIS radiation decay probability.

Scientific Herald of Uzhhorod University Series PhysicsDec 31, 20180 citations

Resonance profiles for electron-ion photorecombination at an isolated resonance

Stanley L. Haan

A projection-operator formalism is employed in studying photorecombination at energies close to an autoionizing resonance. A resonance profile is defined, and is presented without approximation for a model system consisting of one electron continuum, one autoionizing state, and one final radiatively stabilized atomic state. Effective line-profile parameters \ensuremath{\varepsilon}^ and q^ are defined, and the photorecombination resonance profile is shown to be the same as the photoionization resonance profile (for the process in which initial and final atomic states are interchanged from the photorecombination process), provided one-photon spontaneous radiative decay effects are included. The effective line-profile parameters are examined, and are shown to reduce to the standard autoionization line-profile parameters in the limit of no spontaneous radiative decay. Effective line-profile parameters are also defined in the pole approximation for two model systems featuring an isolated autoionizing state. Comparison is made with effective line-profile parameters that have been defined elsewhere in the context of photoionization into coupled electron-continuum channels. The similarity in mathematical formalism for systems supporting multiple continua, regardless of whether these continua are electron or photon continua, is discussed.A projection-operator formalism is employed in studying photorecombination at energies close to an autoionizing resonance. A resonance profile is defined, and is presented without approximation for a model system consisting of one electron continuum, one autoionizing state, and one final radiatively stabilized atomic state. Effective line-profile parameters \ensuremath{\varepsilon}^ and q^ are defined, and the photorecombination resonance profile is shown to be the same as the photoionization resonance profile (for the process in which initial and final atomic states are interchanged from the photorecombination process), provided one-photon spontaneous radiative decay effects are included. The effective line-profile parameters are examined, and are shown to reduce to the standard autoionization line-profile parameters in the limit of no spontaneous radiative decay. Effective line-profile parameters are also defined in the pole approximation for two model systems featuring an isolated autoionizing state. Comparison is made with effective line-profile parameters that have been defined elsewhere in the context of photoionization into coupled electron-continuum channels. The similarity in mathematical formalism for systems supporting multiple continua, regardless of whether these continua are electron or photon continua, is discussed.

Physical Review AOct 1, 19895 citations

Bound state properties, positron annihilation and hyperfine structure splittings in the four-body positron-helium $e^{+} [^{3}$ He( $2^{3}S_e$ )] and $e^{+} [^{4}$ He( $2^{3}S_e$ )] ionsBound state properties, positron annihilation and hyperfine structure splittings in the four-body positron-helium $$e^{+} [^{3}$$He($$2^{3}S_e$$)] and $$e^{+} [^{4}$$He($$2^{3}S_e$$)] ions

Alexei M. Frolov

The European Physical Journal DApr 1, 20251 citation

1s2s2pP2 resonance of He−

Kwong T. Chung

By using a saddle-point technique, the $1s2s2p^{2}P$ resonance of ${\mathrm{He}}^{\ensuremath{-}}$ is found to be a Feshbach resonance. It is formed by the strong coupling of [ $(1s2s)^{1}S$ , $2p$ ] and [ $(1s2p)^{1}P$ , $3d$ ] configurations. By using a seven-partial-wave 54-term wave function and neglecting the open channels, the energy is -2.149 045 a.u. This is higher than the -2.175 23 a.u. $(1s2s)^{3}S$ threshold, but significantly below the -2.145 97 a.u. $(1s2s)^{1}S$ threshold. A quasi-projection-operator method is also carried out. Using the same wave function, the energy is -2.150 54 a.u. These results generally agree with that of experiment.By using a saddle-point technique, the $1s2s2p^{2}P$ resonance of ${\mathrm{He}}^{\ensuremath{-}}$ is found to be a Feshbach resonance. It is formed by the strong coupling of [$(1s2s)^{1}S$,$2p$] and [$(1s2p)^{1}P$,$3d$] configurations. By using a seven-partial-wave 54-term wave function and neglecting the open channels, the energy is -2.149 045 a.u. This is higher than the -2.175 23 a.u. $(1s2s)^{3}S$ threshold, but significantly below the -2.145 97 a.u. $(1s2s)^{1}S$ threshold. A quasi-projection-operator method is also carried out. Using the same wave function, the energy is -2.150 54 a.u. These results generally agree with that of experiment.

Physical Review AMar 1, 198134 citations

Detailed electron-correlation calculations which include the mixing of closed channel with open channels, suggest that

{\mathrm{He}}^{\ensuremath{-}}

has only two bound states: The

1s2s2p^{4}P^{o}

and the

2{p}^{3}^{4}S^{o}

. The

1s2{p}^{2}^{4}P

and

^{2}P

states are above the He

1s2p^{3}P^{o}

threshold and therefore qualify only as core-excited shape resonances. This conclusion contradicts certain previous theoretical and experimental findings which implied the existence of bound

{\mathrm{He}}^{\ensuremath{-}}^{4}P

and

^{2}P

states. Both

^{4}P^{o}

and

^{4}S^{o}

autoionize to the adjacent continuum via spin-dependent forces---a well-known decay mechanism. However, there are two more decay mechanisms: nonrelativistic (for

^{4}S^{o}

) and relativistic (for

^{4}P^{o}

) radiative autoionization (RA). The probability for RA of the

^{4}S^{o}

state in the Hartree-Fock approximation is computed to be 1.14\ifmmode\times\else\texttimes\fi{}

{10}^{10}

{\mathrm{sec}}^{\ensuremath{-}1}

The lifetime of the metastable autodetaching 1s2s2p

^{4}

{\mathit{P}}_{5/2}

level of the $^{4}\mathrm{He}^{\mathrm{\ensuremath{-}}}$ ion has been measured by a time-of-flight technique to be 350\ifmmode\pm\else\textpm\fi{}15 \ensuremath{\mu}s using a heavy-ion storage ring. Blackbody-induced photodetachment of this weakly bound level is shown to influence the decay rate by nearly 20%, an effect not discussed previously. The magnetic-field-induced mixing effects provide additional information about the lifetime of the close-lying

^{4}

{\mathit{P}}_{3/2}

level, yielding \ensuremath{\tau}

{(}^{4}

{\mathit{P}}_{3/2}

)=12\ifmmode\pm\else\textpm\fi{}2 \ensuremath{\mu}s. The observed lifetimes are consistent with previous experimental values, but the accuracy of the

^{4}

{\mathit{P}}_{5/2}

lifetime is improved by a factor of 6, allowing a detailed test of theoretical predictions to be performed. The

^{4}

{\mathit{P}}_{5/2}

lifetime is significantly shorter than most recent advanced theoretical results, but in agreement with a multiconfiguration Hartree-Fock approach accurately describing the initial bound

^{4}

{\mathit{P}}_{5/2}

and the final continuum

^{2}

{\mathit{F}}_{5/2}

states.

Bound state properties, positron annihilation and hyperfine structure splittings in the four-body positron-helium

e^{+} [^{3}

He(

2^{3}S_e

)] and

e^{+} [^{4}

He(

2^{3}S_e

)] ions

By using a saddle-point technique, the

1s2s2p^{2}P

resonance of ${\mathrm{He}}^{\ensuremath{-}}$ is found to be a Feshbach resonance. It is formed by the strong coupling of [

(1s2s)^{1}S

2p

] and [

(1s2p)^{1}P

3d

] configurations. By using a seven-partial-wave 54-term wave function and neglecting the open channels, the energy is -2.149 045 a.u. This is higher than the -2.175 23 a.u.

(1s2s)^{3}S

threshold, but significantly below the -2.145 97 a.u.

(1s2s)^{1}S

threshold. A quasi-projection-operator method is also carried out. Using the same wave function, the energy is -2.150 54 a.u. These results generally agree with that of experiment.