Physical Review A

Direct Demonstration of Spin-Angular-Momentum Conservation in the Reaction He(2S12)+He(2S13)→He(1S01)+He++e−

J. C. Hill, Lynn L. Hatfield, N. D. Stockwell, G. K. Walters

Published Jan 1, 1972• 37 citations

Abstract

Conservation of spin angular momentum in the reaction $\mathrm{He}(2^{2}S_{1})+\mathrm{He}(2^{3}S_{1})\ensuremath{\rightarrow}\mathrm{He}(1^{1}S_{0}+{\mathrm{He}}^{+}+{e}^{\ensuremath{-}}$ is demonstrated quantitatively in the afterglow of a helium discharge by measuring the dependence of the electron production rate upon $2^{3}S_{1}$ spin-state populations, which are manipulated by an optical-pumping technique.

DOI: 10.1103/physreva.5.189

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Physical Review A

Direct Demonstration of Spin-Angular-Momentum Conservation in the Reaction He(2S12)+He(2S13)→He(1S01)+He++e−

J. C. Hill, Lynn L. Hatfield, N. D. Stockwell, G. K. Walters

Published Jan 1, 1972• 37 citations

Publisher

Abstract

Conservation of spin angular momentum in the reaction

\mathrm{He}(2^{2}S_{1})+\mathrm{He}(2^{3}S_{1})\ensuremath{\rightarrow}\mathrm{He}(1^{1}S_{0}+{\mathrm{He}}^{+}+{e}^{\ensuremath{-}}

is demonstrated quantitatively in the afterglow of a helium discharge by measuring the dependence of the electron production rate upon

2^{3}S_{1}

spin-state populations, which are manipulated by an optical-pumping technique.

DOI: 10.1103/physreva.5.189

Related papers

Observation of the Forbidden 2S13→1S01 Spontaneous Emission Line from Helium and Measurement of the Transition Rate

Henry W. Moos, Joseph R. Woodworth

The extremely forbidden transition $2^{3}S_{1}\ensuremath{\rightarrow}^{1}S_{0}$ at 625.56 \AA{} has been observed in a He afterglow using time-resolved high-resolution spectrophotometric techniques. The spontaneous radiative transition rate was determined by measuring the photon emission rate from a known number of metastables at pressures of 0.05, 0.30, and 0.75 Torr. The value measured is 2.4\ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}4}$ ${\mathrm{sec}}^{\ensuremath{-}1}$ with an experimental uncertainty of a factor of 3.The extremely forbidden transition $2^{3}S_{1}\ensuremath{\rightarrow}^{1}S_{0}$ at 625.56 \AA{} has been observed in a He afterglow using time-resolved high-resolution spectrophotometric techniques. The spontaneous radiative transition rate was determined by measuring the photon emission rate from a known number of metastables at pressures of 0.05, 0.30, and 0.75 Torr. The value measured is 2.4\ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}4}$ ${\mathrm{sec}}^{\ensuremath{-}1}$ with an experimental uncertainty of a factor of 3.

Physical Review LettersApr 23, 197346 citations

Low-Energy Inelastic Scattering of He(2 S3) on He(1 S1)

R. E. Olson, Reinhard Morgenstern, D. C. Lorents +2 more

Time-of-flight scattering measurements at 8.65 eV (c.m.) display strong inelastic scattering from $\mathrm{He}(2 ^{3}S)+\mathrm{He}(1 ^{1}S)$ to $\mathrm{He}(2 ^{3}P)+\mathrm{He}(1 ^{1}S)$ . Close-coupled quantum-mechanical calculations employing ab initio potential curves and matrix elements show the inelastic process is due to strong rotational coupling between the $c ^{3}\ensuremath{\Sigma}_{g}^{+}$ state of $\mathrm{He}(2 ^{3}S)+\mathrm{He}(1 ^{1}S)$ and the $b ^{3}\ensuremath{\Pi}_{g}$ state of $\mathrm{He}(2 ^{3}P)+\mathrm{He}(1 ^{1}S)$ . Good agreement is found between the calculated and the experimentally measured inelastic-scattering cross sections.Time-of-flight scattering measurements at 8.65 eV (c.m.) display strong inelastic scattering from $\mathrm{He}(2 ^{3}S)+\mathrm{He}(1 ^{1}S)$ to $\mathrm{He}(2 ^{3}P)+\mathrm{He}(1 ^{1}S)$. Close-coupled quantum-mechanical calculations employing ab initio potential curves and matrix elements show the inelastic process is due to strong rotational coupling between the $c ^{3}\ensuremath{\Sigma}_{g}^{+}$ state of $\mathrm{He}(2 ^{3}S)+\mathrm{He}(1 ^{1}S)$ and the $b ^{3}\ensuremath{\Pi}_{g}$ state of $\mathrm{He}(2 ^{3}P)+\mathrm{He}(1 ^{1}S)$. Good agreement is found between the calculated and the experimentally measured inelastic-scattering cross sections.

Physical Review ANov 1, 197311 citations

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L. G. Gray, Karl Giberson, Chu Cheng +3 more

A source of spin-polarized electrons based on a laser-pumped flowing helium afterglow is described. He(23S) atoms contained in the afterglow are optically pumped using circularly polarized 1.08-μm (23S→23P) radiation provided by a NaF (F2+)* color-center laser. Spin angular momentum conservation in subsequent chemi-ionization reactions with CO2 produces polarized electrons that are extracted from the afterglow. At low currents, ≲1 μA, polarizations of ∼70%–80% are achieved. At higher currents the polarization decreases, falling to ∼40% at 50 μA. The spin polarization can be simply reversed (P→−P) and the source is suitable for use in the majority of low-energy spin-dependent scattering experiments proposed to date.A source of spin-polarized electrons based on a laser-pumped flowing helium afterglow is described. He(23S) atoms contained in the afterglow are optically pumped using circularly polarized 1.08-μm (23S→23P) radiation provided by a NaF (F2+)* color-center laser. Spin angular momentum conservation in subsequent chemi-ionization reactions with CO2 produces polarized electrons that are extracted from the afterglow. At low currents, ≲1 μA, polarizations of ∼70%–80% are achieved. At higher currents the polarization decreases, falling to ∼40% at 50 μA. The spin polarization can be simply reversed (P→−P) and the source is suitable for use in the majority of low-energy spin-dependent scattering experiments proposed to date.

Review of Scientific InstrumentsMar 1, 198332 citations

On the limits of spin-exchange optical pumping of $^{3}$ HeOn the limits of spin-exchange optical pumping of $^{3}$He

T. Gentile, Wangchun Chen, Q. Ye +2 more

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An experimental determination of gJ(He4, 2S13)gJ(H1, 1S122)

George M. Keiser, H. G. Robinson, C. E. Johnson

The ratio of the ${g}_{J}$ factor of $^{4}\mathrm{He}(2^{3}S_{1})$ to that of $^{87}\mathrm{Rb}(5^{2}S_{\frac{1}{2}})$ has been measured to a fractional accuracy of \ifmmode\pm\else\textpm\fi{}5\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}8}$. The Rb atoms were optically pumped, and the $^{4}\mathrm{He}(2^{3}S_{1})$ Zeeman resonance was observed through a combination of spin-exchange collisions and spin-dependent Penning ionization. Linewidths as narrow as 220 Hz were observed for the $^{4}\mathrm{He}(2^{3}S_{1})$ Zeeman resonance. The accuracy of this experiment was limited by a systematic shift in the He ${g}_{J}$ factor that depended upon the intensity of the discharge used to excite the He atoms to the $2^{3}S_{1}$ state. Calculations indicate that transfer of coherence in spin-exchange collisions with free electrons contributes to this shift. The measured ratio $\frac{{g}_{J}(^{4}\mathrm{He}, 2^{3}S_{1})}{{g}_{J}(^{87}\mathrm{Rb}, 5^{2}S_{\frac{1}{2}})}=1\ensuremath{-}46.798(50)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$. Using the previously measured ratio of the ${g}_{J}$ factors of the ground state of rubidium to the ground state of hydrogen, we determine the ratio $\frac{{g}_{J}(^{4}\mathrm{He}, 2^{3}S_{1})}{{g}_{J}(^{1}\mathrm{H}, 1^{2}S_{\frac{1}{2}})}=1\ensuremath{-}23.214(50)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$. This result agrees with recent theoretical calculations and experimental determinations using atomic-beam techniques, but disagrees with an earlier experimental determination using optical-pumping techniques.The ratio of the ${g}_{J}$ factor of $^{4}\mathrm{He}(2^{3}S_{1})$ to that of $^{87}\mathrm{Rb}(5^{2}S_{\frac{1}{2}})$ has been measured to a fractional accuracy of \ifmmode\pm\else\textpm\fi{}5\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}8}$. The Rb atoms were optically pumped, and the $^{4}\mathrm{He}(2^{3}S_{1})$ Zeeman resonance was observed through a combination of spin-exchange collisions and spin-dependent Penning ionization. Linewidths as narrow as 220 Hz were observed for the $^{4}\mathrm{He}(2^{3}S_{1})$ Zeeman resonance. The accuracy of this experiment was limited by a systematic shift in the He ${g}_{J}$ factor that depended upon the intensity of the discharge used to excite the He atoms to the $2^{3}S_{1}$ state. Calculations indicate that transfer of coherence in spin-exchange collisions with free electrons contributes to this shift. The measured ratio $\frac{{g}_{J}(^{4}\mathrm{He}, 2^{3}S_{1})}{{g}_{J}(^{87}\mathrm{Rb}, 5^{2}S_{\frac{1}{2}})}=1\ensuremath{-}46.798(50)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$. Using the previously measured ratio of the ${g}_{J}$ factors of the ground state of rubidium to the ground state of hydrogen, we determine the ratio $\frac{{g}_{J}(^{4}\mathrm{He}, 2^{3}S_{1})}{{g}_{J}(^{1}\mathrm{H}, 1^{2}S_{\frac{1}{2}})}=1\ensuremath{-}23.214(50)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$. This result agrees with recent theoretical calculations and experimental determinations using atomic-beam techniques, but disagrees with an earlier experimental determination using optical-pumping techniques.

Physical Review ASep 1, 197722 citations

Conservation of spin angular momentum in the reaction

\mathrm{He}(2^{2}S_{1})+\mathrm{He}(2^{3}S_{1})\ensuremath{\rightarrow}\mathrm{He}(1^{1}S_{0}+{\mathrm{He}}^{+}+{e}^{\ensuremath{-}}

is demonstrated quantitatively in the afterglow of a helium discharge by measuring the dependence of the electron production rate upon

2^{3}S_{1}

spin-state populations, which are manipulated by an optical-pumping technique.

Time-of-flight scattering measurements at 8.65 eV (c.m.) display strong inelastic scattering from

\mathrm{He}(2 ^{3}S)+\mathrm{He}(1 ^{1}S)

\mathrm{He}(2 ^{3}P)+\mathrm{He}(1 ^{1}S)

. Close-coupled quantum-mechanical calculations employing ab initio potential curves and matrix elements show the inelastic process is due to strong rotational coupling between the $c ^{3}\ensuremath{\Sigma}_{g}^{+}$ state of

\mathrm{He}(2 ^{3}S)+\mathrm{He}(1 ^{1}S)

and the $b ^{3}\ensuremath{\Pi}_{g}$ state of

\mathrm{He}(2 ^{3}P)+\mathrm{He}(1 ^{1}S)

. Good agreement is found between the calculated and the experimentally measured inelastic-scattering cross sections.

On the limits of spin-exchange optical pumping of

^{3}

The ratio of the

{g}_{J}

factor of

^{4}\mathrm{He}(2^{3}S_{1})

to that of

^{87}\mathrm{Rb}(5^{2}S_{\frac{1}{2}})

has been measured to a fractional accuracy of \ifmmode\pm\else\textpm\fi{}5\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}8}$. The Rb atoms were optically pumped, and the

^{4}\mathrm{He}(2^{3}S_{1})

Zeeman resonance was observed through a combination of spin-exchange collisions and spin-dependent Penning ionization. Linewidths as narrow as 220 Hz were observed for the

^{4}\mathrm{He}(2^{3}S_{1})

Zeeman resonance. The accuracy of this experiment was limited by a systematic shift in the He

{g}_{J}

factor that depended upon the intensity of the discharge used to excite the He atoms to the

2^{3}S_{1}

state. Calculations indicate that transfer of coherence in spin-exchange collisions with free electrons contributes to this shift. The measured ratio $\frac{{g}_{J}(^{4}\mathrm{He}, 2^{3}S_{1})}{{g}_{J}(^{87}\mathrm{Rb}, 5^{2}S_{\frac{1}{2}})}=1\ensuremath{-}46.798(50)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$. Using the previously measured ratio of the

{g}_{J}

factors of the ground state of rubidium to the ground state of hydrogen, we determine the ratio $\frac{{g}_{J}(^{4}\mathrm{He}, 2^{3}S_{1})}{{g}_{J}(^{1}\mathrm{H}, 1^{2}S_{\frac{1}{2}})}=1\ensuremath{-}23.214(50)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$. This result agrees with recent theoretical calculations and experimental determinations using atomic-beam techniques, but disagrees with an earlier experimental determination using optical-pumping techniques.