Physical Review A

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

Helen K. Holt

Published Aug 1, 1983• 0 citations

Abstract

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.

DOI: 10.1103/physreva.28.1157

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Time-Dependent Theory of Stark Quenching of 2S States in Hydrogen and Helium

Helen K. Holt, Ivan A. Sellin

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Quenching of the 2S01 Metastable State of Helium by an Electric Field

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Metastability of Hydrogen and Helium Levels.

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Coherent excitation of two n=3 Stark states in a fast hydrogen beam and their evolution inside a time-dependent electric field

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Journal of Physics B Atomic and Molecular PhysicsApr 28, 19872 citations

Physical Review A

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

Helen K. Holt

Published Aug 1, 1983• 0 citations

Publisher

Abstract

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.

DOI: 10.1103/physreva.28.1157

Related papers

Time-Dependent Theory of Stark Quenching of 2S States in Hydrogen and Helium

Helen K. Holt, Ivan A. Sellin

A nonperturbative time-dependent theory which gives Stark-quenching lifetimes in agreement with experiment for both one- and two-electron $2S$ states is presented. This theory differs from the conventional Bethe-Lamb theory of Stark quenching, but reduces to this older theory, for one electron atoms only, when a well-known sum rule is applied.A nonperturbative time-dependent theory which gives Stark-quenching lifetimes in agreement with experiment for both one- and two-electron $2S$ states is presented. This theory differs from the conventional Bethe-Lamb theory of Stark quenching, but reduces to this older theory, for one electron atoms only, when a well-known sum rule is applied.

Physical Review AJul 1, 197219 citations

Quenching of the 2S01 Metastable State of Helium by an Electric Field

Charles E. Johnson

A time-of-flight technique has been used to measure the quenching of the $2^{1}S_{0}$ metastable state of helium by a static electric field. Neutral ground-state helium atoms effusing from a cooled source slit are immediately excited to the $2^{1}S_{0}$ and $2^{3}S_{1}$ metastable states by a pulse of antiparallel magnetically focused electrons. The metastable beam is collimated before passing through a uniform electric field region 0.5 m long and is then preferentially detected at the end of the time-of-flight region, 1.825 m from the electron gun. The time-of-flight distribution for the $2^{1}S_{0}$ state is separated from that of the $2^{3}S_{1}$ state by illuminating the beam before the electric field region with an rf-discharge helium lamp. The $2^{1}S_{0}$ state is quenched by resonant absorption of a 20 581-\AA{} photon, raising the atom to the $2^{1}P_{1}$ state, which then decays to the $^{1}S_{0}$ ground state; the $2^{3}S_{1}$ state remains unaffected because it is the ground state for the triplet system. The $2^{1}S_{0}$ time-of-flight distribution is therefore obtained from the difference between the full beam and the quenched beam. The number of $2^{1}S_{0}$ atoms arriving at the detector in specific velocity intervals with the electric field off is compared to the number with the field on to determine the quenching rate ( $=k{E}^{2}$ ). The result for the quenching constant $k$ for both ${\mathrm{He}}^{3}$ and ${\mathrm{He}}^{4}$ with $E$ in kV/cm is $k=0.933\ifmmode\pm\else\textpm\fi{}0.005$; this value is in good agreement with theory and with an earlier less accurate experiment. The error in the present experiment arises from a 0.5% uncertainty in the effective length of the electric field region.A time-of-flight technique has been used to measure the quenching of the $2^{1}S_{0}$ metastable state of helium by a static electric field. Neutral ground-state helium atoms effusing from a cooled source slit are immediately excited to the $2^{1}S_{0}$ and $2^{3}S_{1}$ metastable states by a pulse of antiparallel magnetically focused electrons. The metastable beam is collimated before passing through a uniform electric field region 0.5 m long and is then preferentially detected at the end of the time-of-flight region, 1.825 m from the electron gun. The time-of-flight distribution for the $2^{1}S_{0}$ state is separated from that of the $2^{3}S_{1}$ state by illuminating the beam before the electric field region with an rf-discharge helium lamp. The $2^{1}S_{0}$ state is quenched by resonant absorption of a 20 581-\AA{} photon, raising the atom to the $2^{1}P_{1}$ state, which then decays to the $^{1}S_{0}$ ground state; the $2^{3}S_{1}$ state remains unaffected because it is the ground state for the triplet system. The $2^{1}S_{0}$ time-of-flight distribution is therefore obtained from the difference between the full beam and the quenched beam. The number of $2^{1}S_{0}$ atoms arriving at the detector in specific velocity intervals with the electric field off is compared to the number with the field on to determine the quenching rate ($=k{E}^{2}$). The result for the quenching constant $k$ for both ${\mathrm{He}}^{3}$ and ${\mathrm{He}}^{4}$ with $E$ in kV/cm is $k=0.933\ifmmode\pm\else\textpm\fi{}0.005$; this value is in good agreement with theory and with an earlier less accurate experiment. The error in the present experiment arises from a 0.5% uncertainty in the effective length of the electric field region.

Physical Review AMar 1, 197310 citations

Metastability of Hydrogen and Helium Levels.

GREGORY A. BREIT, Edward Teller

The mean life of the 2S state of hydrogen in the absence of collisions is primarily determined by the simultaneous emission of two photons. Owing to this cause the mean life is `-*4 sec. It is expected that the mean life of is 2S `S of He i is of the same order of magnitude and is much shorter than that of is 2S 3S of He i. The non-adiabatic collisions with electrons are found to be more important than the static effects at small electron densities, leading to a transition probability `-*-`~h sec ` for an electron temper- ature `-.--`io,ooo° C and an electron density 30 cm3. The effect of static electric fields on the 2S state of hydrogen is worked out in more detail than previously by taking into account the hyperfine structure. The mean life in static electric fields which are strong enough to make double emission of little importance and yet weak enough to give a mean life > io7 sec is found to be the sum of two lives: (i) the mean life calculated neglecting hyperfine structure and (2) the mean life calculated neglecting radiation coupling. In both (i) and (2) the mixing of 2~ into 2S by the Stark effect is taken into account. Radiations due to quadrupole and magnetic dipole effects are considered qualita- tively for is 2S 3S of helium and quantitatively for 2S of hydrogen. For the latter there exists a small radiative magnetic dipole effect on Dirac's theory of the electron which is absent in the ordinary spin modelThe mean life of the 2S state of hydrogen in the absence of collisions is primarily determined by the simultaneous emission of two photons. Owing to this cause the mean life is `-*4 sec. It is expected that the mean life of is 2S `S of He i is of the same order of magnitude and is much shorter than that of is 2S 3S of He i. The non-adiabatic collisions with electrons are found to be more important than the static effects at small electron densities, leading to a transition probability `-*-`~h sec ` for an electron temper- ature `-.--`io,ooo° C and an electron density 30 cm3. The effect of static electric fields on the 2S state of hydrogen is worked out in more detail than previously by taking into account the hyperfine structure. The mean life in static electric fields which are strong enough to make double emission of little importance and yet weak enough to give a mean life > io7 sec is found to be the sum of two lives: (i) the mean life calculated neglecting hyperfine structure and (2) the mean life calculated neglecting radiation coupling. In both (i) and (2) the mixing of 2~ into 2S by the Stark effect is taken into account. Radiations due to quadrupole and magnetic dipole effects are considered qualita- tively for is 2S 3S of helium and quantitatively for 2S of hydrogen. For the latter there exists a small radiative magnetic dipole effect on Dirac's theory of the electron which is absent in the ordinary spin model

The Astrophysical JournalMar 1, 1940337 citations

Non-adiabatic 2s-2p state mixing in metastable hydrogen by electric fields

Freddy Brouillard, G. Van Wassenhove

The evolution of a (n=2) hydrogen atom passing through a linearly increasing or decreasing electric field is calculated in a three-state approximation. The observable fraction of 2p 1/2 , 2s 1/2 and 2p 3/2 quantum state in the resulting coherent mixture is calculated. The amplitude of the oscillations, which appear when the field parameters are varied, is shown to depend only on the rate of change of the field, as seen by the atom. Maps of oscillation amplitudes and average values are given for the metastable atom. Comparison is made with the sudden and adiabatic approximations.The evolution of a (n=2) hydrogen atom passing through a linearly increasing or decreasing electric field is calculated in a three-state approximation. The observable fraction of 2p 1/2 , 2s 1/2 and 2p 3/2 quantum state in the resulting coherent mixture is calculated. The amplitude of the oscillations, which appear when the field parameters are varied, is shown to depend only on the rate of change of the field, as seen by the atom. Maps of oscillation amplitudes and average values are given for the metastable atom. Comparison is made with the sudden and adiabatic approximations.

Journal of Physics B Atomic and Molecular PhysicsDec 1, 19744 citations

Quenching of metastable He+ 2s ions by molecules

Govind P. Gupta, K. C. Mathur

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.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.

Physical Review AMay 1, 19813 citations

Coherent excitation of two n=3 Stark states in a fast hydrogen beam and their evolution inside a time-dependent electric field

V. Lorent, W. Claeys, A Cornet +1 more

The authors studied in an earlier paper (1985) the production of a fast beam of H(3s) atoms. They investigated the particular problem of a coherent laser excitation of the 3s 1/2 and 3p 1/2 Stark states from the 2s 1/2 metastable Stark state. They measured the 3s 1/2 fluorescence outside the electric field and quantal interference effects have been observed as a function of the electric field strength. A simple theoretical interpretation is proposed which takes into account the quasi-adiabatic evolution of the atom in the electric field under the authors' experimental conditions.The authors studied in an earlier paper (1985) the production of a fast beam of H(3s) atoms. They investigated the particular problem of a coherent laser excitation of the 3s 1/2 and 3p 1/2 Stark states from the 2s 1/2 metastable Stark state. They measured the 3s 1/2 fluorescence outside the electric field and quantal interference effects have been observed as a function of the electric field strength. A simple theoretical interpretation is proposed which takes into account the quasi-adiabatic evolution of the atom in the electric field under the authors' experimental conditions.

Journal of Physics B Atomic and Molecular PhysicsApr 28, 19872 citations

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.

A nonperturbative time-dependent theory which gives Stark-quenching lifetimes in agreement with experiment for both one- and two-electron

2S

states is presented. This theory differs from the conventional Bethe-Lamb theory of Stark quenching, but reduces to this older theory, for one electron atoms only, when a well-known sum rule is applied.

A time-of-flight technique has been used to measure the quenching of the

2^{1}S_{0}

metastable state of helium by a static electric field. Neutral ground-state helium atoms effusing from a cooled source slit are immediately excited to the

2^{1}S_{0}

and

2^{3}S_{1}

metastable states by a pulse of antiparallel magnetically focused electrons. The metastable beam is collimated before passing through a uniform electric field region 0.5 m long and is then preferentially detected at the end of the time-of-flight region, 1.825 m from the electron gun. The time-of-flight distribution for the

2^{1}S_{0}

state is separated from that of the

2^{3}S_{1}

state by illuminating the beam before the electric field region with an rf-discharge helium lamp. The

2^{1}S_{0}

state is quenched by resonant absorption of a 20 581-\AA{} photon, raising the atom to the

2^{1}P_{1}

state, which then decays to the

^{1}S_{0}

ground state; the

2^{3}S_{1}

state remains unaffected because it is the ground state for the triplet system. The

2^{1}S_{0}

time-of-flight distribution is therefore obtained from the difference between the full beam and the quenched beam. The number of

2^{1}S_{0}

atoms arriving at the detector in specific velocity intervals with the electric field off is compared to the number with the field on to determine the quenching rate (

=k{E}^{2}

). The result for the quenching constant

k

for both

{\mathrm{He}}^{3}

and

{\mathrm{He}}^{4}

with

E

in kV/cm is $k=0.933\ifmmode\pm\else\textpm\fi{}0.005$; this value is in good agreement with theory and with an earlier less accurate experiment. The error in the present experiment arises from a 0.5% uncertainty in the effective length of the electric field region.

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.