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Physical Review A

Alignment of ions in Penning collisions

David W. Fahey, L. D. Schearer, W. F. Parks

Published Oct 1, 1979• 3 citations
Publisher

Abstract

The authors have observed the alignment of the $5p^{2}P_{\frac{3}{2}}$ state of strontium ions produced in Penning collisions between an unpolarized beam of helium metastable atoms and a strontium vapor target. The alignment is shown by a linear polarization of the optical emission from the excited ion. For a 66-meV beam of helium metastable atoms a 3.5% linear polarization of the emission relative to the beam axis was measured. It is shown how the alignment may be used to determine the probabilities for populating the various final quasimolecular states of the ion-atom pair. The alignment of the Penning ions is an important new parameter in the description of these reactions.

DOI
10.1103/physreva.20.1372

Related papers

Coherence in Penning Ionization and First Kind Collisions: Volume Recombination of Ions/Electrons.

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A thermal energy beam of helium atoms in the metastable state is used to coherently excite ions of Sr, Ca, and Ba in a Penning collision. The anisotropic excited state distributions appears as Polarized line emission from the excited ions. The degree of ion alignment may be used to determine the populations of the quasi-molecular states of the ion-atom pair. The coherent emission is also utilized to obtain Hanle signals from which the radiative decay rate of the excited ion is determined. This is the first case in which coherence is produced in a collision process involving Penning ionization. The alignment of the Penning ions is an important new parameter in the description of these reactions. In an effort to extend such observations to molecular systems a nitrogen molecular metastable beam source was demonstrated. The use of metal vapor targets and the excitation rate of the excited states of Cd and Zn in energy transfer collisions with the N2(m) enable us to determine the vibrational distribution of the A 3Sigma state of N2 in the beam. Energy transfer cross sections and some Penning cross sections were measured in the beam system. (Author)

•Dec 1, 1979•0 citations

Coherence in penning ionization and first kind collisions: volume recombination of ions/electrons. Technical report no. 12, dec 78-dec 79

L. D. Schearer, W. F. Parks

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A thermal beam of helium (2 3 S 1 ) metastable atoms was used to excite coherently the 2 P 3/2 levels of Ca, Sr and Ba in a Penning ionising collision. The coherent excitation of the ions appears as a linear polarisation of the optical emission from the excited ions. The degree of linear polarisation is 5.5, 3.5 and 0.5% for Ca, Sr and Ba, respectively, with the polarisation parallel to the beam direction. Hanle effect signals from the 2 P 3/2 level of Sr were observed and the radioactive decay rate measured.

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Effects of alignment on strontium energy pooling collisions

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The dependence of energy pooling cross sections on the alignment of atomic angular momentum with respect to the collision axis is investigated. In a vapor cell, excitation with counter-propagating polarized laser beams that define the collision axis prepares aligned strontium atoms in the $5s5p{}^{3}{P}_{1}$ level. Excited-state energy pooling collision products from the endothermic $5s5p{}^{3}{P}_{1}+5s5p{}^{3}{P}_{1}\ensuremath{\rightarrow}5s6s{}^{1}{S}_{0}{+5s}^{2}{}^{1}{S}_{0}$ reaction and the exothermic $5s5p{}^{3}{P}_{1}+5s5p{}^{3}{P}_{1}\ensuremath{\rightarrow}5s5p{}^{1}{P}_{1}{+5s}^{2}{}^{1}{S}_{0}$ reaction are studied. Alignment effects are studied as a function of collision energy, using pulsed laser excitation followed by delayed fluorescence detection to lower the transverse collision velocity and laser detuning to vary the collision velocity in the laser-beam direction. The rate coefficient for energy transfer to the $6{}^{1}{S}_{0}$ state is enhanced by $38\ifmmode\pm\else\textpm\fi{}13%$ when the ${M}_{J}$ alignment of the collision partners is perpendicular to the collision axis and parallel to each other compared to when there is no alignment of the collision partners. No alignment dependence is observed for energy transfer to the $5{}^{1}{P}_{1}$ state. This experiment offers the unique capability of simultaneously and independently controlling collision velocity and angular momentum alignment.

Physical Review A•Mar 1, 1998•2 citations

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Modulation of the intensity of light emitted by ${\mathrm{Sr}}^{+}(^{2}P_{\frac{3}{2}})$ ions at the resonance frequency of metastable helium atoms has been observed, demonstrating that coherence has been transferred in the Penning collision. The coherent excitation of the Penning ions suggests that the techniques of "coherence spectroscopy" such as level-crossing and Hanle experiments can be extended to excited states of Penning ions which are currently inaccessible by means of optical excitation.

Physical Review Letters•Mar 15, 1971•24 citations
The authors have observed the alignment of the 5p2P325p^{2}P_{\frac{3}{2}}5p2P23​​ state of strontium ions produced in Penning collisions between an unpolarized beam of helium metastable atoms and a strontium vapor target. The alignment is shown by a linear polarization of the optical emission from the excited ion. For a 66-meV beam of helium metastable atoms a 3.5% linear polarization of the emission relative to the beam axis was measured. It is shown how the alignment may be used to determine the probabilities for populating the various final quasimolecular states of the ion-atom pair. The alignment of the Penning ions is an important new parameter in the description of these reactions.
A thermal energy beam of helium atoms in the metastable state is used to coherently excite ions of Sr, Ca, and Ba in a Penning collision. The anisotropic excited state distributions appears as Polarized line emission from the excited ions. The degree of ion alignment may be used to determine the populations of the quasi-molecular states of the ion-atom pair. The coherent emission is also utilized to obtain Hanle signals from which the radiative decay rate of the excited ion is determined. This is the first case in which coherence is produced in a collision process involving Penning ionization. The alignment of the Penning ions is an important new parameter in the description of these reactions. In an effort to extend such observations to molecular systems a nitrogen molecular metastable beam source was demonstrated. The use of metal vapor targets and the excitation rate of the excited states of Cd and Zn in energy transfer collisions with the N2(m) enable us to determine the vibrational distribution of the A 3Sigma state of N2 in the beam. Energy transfer cross sections and some Penning cross sections were measured in the beam system. (Author)
A thermal-energy beam of helium atoms in the metastable state is used to coherently excite ions of Sr, Ca, and Ba in a Penning collision. The anisotropic excited state distributions appears as Polarized line emission from the excited ions. The degree of ion alignment may be used to determine the populations of the quasi-molecular states of the ion-atom pair. The coherent emission is also utilized to obtain Hanle signals from which the radiative decay rate of the excited ion is determined. This is the first case in which coherence is produced in a collision process involving Penning ionization. The alignment of the Penning ions is an important new parameter in the description of these reactions. In an effort to extend such observations to molecular systems a nitrogen molecular metastable beam source was demonstrated. The use of metal vapor targets and the excitation rate of the excited states of Cd and Zn in energy transfer collisions with the N2/sub (m)/ enable us to determine the vibrational distribution of the A /sup 3/SIGMA state of N/sub 2/ in the beam. Energy transfer cross sections and some Penning cross sections were measured in the beam system.
A thermal beam of helium (2 3 S 1 ) metastable atoms was used to excite coherently the 2 P 3/2 levels of Ca, Sr and Ba in a Penning ionising collision. The coherent excitation of the ions appears as a linear polarisation of the optical emission from the excited ions. The degree of linear polarisation is 5.5, 3.5 and 0.5% for Ca, Sr and Ba, respectively, with the polarisation parallel to the beam direction. Hanle effect signals from the 2 P 3/2 level of Sr were observed and the radioactive decay rate measured.
The dependence of energy pooling cross sections on the alignment of atomic angular momentum with respect to the collision axis is investigated. In a vapor cell, excitation with counter-propagating polarized laser beams that define the collision axis prepares aligned strontium atoms in the 5s5p3P15s5p{}^{3}{P}_{1}5s5p3P1​ level. Excited-state energy pooling collision products from the endothermic $5s5p{}^{3}{P}_{1}+5s5p{}^{3}{P}_{1}\ensuremath{\rightarrow}5s6s{}^{1}{S}_{0}{+5s}^{2}{}^{1}{S}_{0}$ reaction and the exothermic $5s5p{}^{3}{P}_{1}+5s5p{}^{3}{P}_{1}\ensuremath{\rightarrow}5s5p{}^{1}{P}_{1}{+5s}^{2}{}^{1}{S}_{0}$ reaction are studied. Alignment effects are studied as a function of collision energy, using pulsed laser excitation followed by delayed fluorescence detection to lower the transverse collision velocity and laser detuning to vary the collision velocity in the laser-beam direction. The rate coefficient for energy transfer to the 61S06{}^{1}{S}_{0}61S0​ state is enhanced by $38\ifmmode\pm\else\textpm\fi{}13%$ when the MJ{M}_{J}MJ​ alignment of the collision partners is perpendicular to the collision axis and parallel to each other compared to when there is no alignment of the collision partners. No alignment dependence is observed for energy transfer to the 51P15{}^{1}{P}_{1}51P1​ state. This experiment offers the unique capability of simultaneously and independently controlling collision velocity and angular momentum alignment.
Transfer of spin polarization from optically pumped metastable helium atoms to the ions of Cd, Sr, and Zn following Penning collisions has been demonstrated indicating that a component of spin angular momentum is conserved. The ion polarization, detected optically, exceeds 10% at ion concentrations on the order of 1010{10}^{10}1010-1011{10}^{11}1011 ${\mathrm{cm}}^{\ensuremath{-}3}$.
Modulation of the intensity of light emitted by Sr+(2P32){\mathrm{Sr}}^{+}(^{2}P_{\frac{3}{2}})Sr+(2P23​​) ions at the resonance frequency of metastable helium atoms has been observed, demonstrating that coherence has been transferred in the Penning collision. The coherent excitation of the Penning ions suggests that the techniques of "coherence spectroscopy" such as level-crossing and Hanle experiments can be extended to excited states of Penning ions which are currently inaccessible by means of optical excitation.