Physical Review Letters

Influence of Coherence on Associative Ionization in Na(3p)+Na(3p) Collisions

Harro A. J. Meijer, T. J. C. Pelgrim, H G M Heideman, Reinhard Morgenstern, N. Andersen

Published Dec 28, 1987• 20 citations

Abstract

We have investigated the associative ionization of Na atoms in two counterpropagating thermal beams independently excited by various combinations of linearly and circularly polarized light. In this way information about coherence contributions to the ion signal has been obtained for the first time. These contributions which correspond to off-diagonal elements of the detection matrix have hitherto been neglected, but are of the same magnitude as the cross sections themselves and depend on the velocity.

DOI: 10.1103/physrevlett.59.2939

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Physical Review Letters

Influence of Coherence on Associative Ionization in Na(3p)+Na(3p) Collisions

Harro A. J. Meijer, T. J. C. Pelgrim, H G M Heideman, Reinhard Morgenstern, N. Andersen

Published Dec 28, 1987• 20 citations

Publisher

Abstract

DOI: 10.1103/physrevlett.59.2939

Related papers

Cross sections and coherences for energy pooling reactions between two Na*(3p) atoms

J H Nijland, J. A. de Gouw, H.A. Dijkerman +1 more

The authors have studied, in a beam experiment, the energy pooling reaction between two laser excited Na*(3p) atoms, where in the final state one of the Na atoms is in the 5s or 4d state and the other in the ground state. The polarization of the Na*(3p) atoms can be varied by changing the laser polarization. By using two counterpropagating Na beams and intersecting them twice by a laser beam (directly and indirectly after reflection against a mirror) the polarization of the two collision partners can be varied independently. Since the laser beam intersects the Na beams at an angle of 87.6 degrees , the relative velocity of the atoms can furthermore be selected by exploiting the Doppler effect. In the authors' experiment the relevant cross sections and coherences, specified according to the various magnetic substate combinations of the colliding Na*(3p) atoms, can be determined.The authors have studied, in a beam experiment, the energy pooling reaction between two laser excited Na*(3p) atoms, where in the final state one of the Na atoms is in the 5s or 4d state and the other in the ground state. The polarization of the Na*(3p) atoms can be varied by changing the laser polarization. By using two counterpropagating Na beams and intersecting them twice by a laser beam (directly and indirectly after reflection against a mirror) the polarization of the two collision partners can be varied independently. Since the laser beam intersects the Na beams at an angle of 87.6 degrees , the relative velocity of the atoms can furthermore be selected by exploiting the Doppler effect. In the authors' experiment the relevant cross sections and coherences, specified according to the various magnetic substate combinations of the colliding Na*(3p) atoms, can be determined.

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We report cross-section measurements of the associative-ionization process, Na(3 ${\mathit{p}}^{2}$ ${\mathit{P}}_{3/2}$ )+Na(3 ${\mathit{p}}^{2}$ ${\mathit{P}}_{3/2}$ )\ensuremath{\rightarrow} ${\mathrm{Na}}_{2}^{+}$ +e as a function of velocity, alignment, and orientation in the collision energy range from 300 to 5 K. Two independently tunable laser beams select narrow velocity classes of excited sodium in a well-collimated atomic beam. Circular and linear polarization of the excitation lasers permits alignment and orientation of the excited atoms in the two velocity classes. The excitation functions show pronounced differences reflecting different molecular pathways to the final product, and they bridge the energy range between conventional and ``cold'' collision dynamics.We report cross-section measurements of the associative-ionization process, Na(3${\mathit{p}}^{2}$${\mathit{P}}_{3/2}$)+Na(3${\mathit{p}}^{2}$${\mathit{P}}_{3/2}$)\ensuremath{\rightarrow}${\mathrm{Na}}_{2}^{+}$+e as a function of velocity, alignment, and orientation in the collision energy range from 300 to 5 K. Two independently tunable laser beams select narrow velocity classes of excited sodium in a well-collimated atomic beam. Circular and linear polarization of the excitation lasers permits alignment and orientation of the excited atoms in the two velocity classes. The excitation functions show pronounced differences reflecting different molecular pathways to the final product, and they bridge the energy range between conventional and ``cold'' collision dynamics.

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M-X. Wang, J. Keller, Jacques Boulmer +1 more

We report new results on the direct measurement of the associative ionization (AI) cross section in collisions between velocity-selected and spin-oriented Na(3p) atoms. Improvements in the Doppler-shift velocity-selection technique permit measurement over an energy range spanning more than two orders of magnitude from subthermal to suprathermal regions. Spin orientations, parallel and antiparallel, enable determination of the excitation function (velocity dependence of the AI cross section) for the separate singlet and triplet manifolds of ${\mathrm{Na}}_{2}$ states contributing to the AI process.We report new results on the direct measurement of the associative ionization (AI) cross section in collisions between velocity-selected and spin-oriented Na(3p) atoms. Improvements in the Doppler-shift velocity-selection technique permit measurement over an energy range spanning more than two orders of magnitude from subthermal to suprathermal regions. Spin orientations, parallel and antiparallel, enable determination of the excitation function (velocity dependence of the AI cross section) for the separate singlet and triplet manifolds of ${\mathrm{Na}}_{2}$ states contributing to the AI process.

Physical Review AJan 1, 198731 citations

K

obey the relations

K(\frac{1}{2}, \frac{3}{2})=0

and

K(\frac{1}{2}, \frac{1}{2})=1.4K(\frac{3}{2}, \frac{3}{2})

, where the arguments indicate the initial magnetic substates

|{M}_{J}|

of the two colliding atoms.

{K}_{65\mathrm{m}\mathrm{K}{}^{\mathrm{lin}}}

=(12.2\ifmmode\pm\else\textpm\fi{}4.3)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}13}$

{\mathrm{cm}}^{3}

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

{K}_{65\mathrm{m}\mathrm{K}{}^{\mathrm{cir}}}

=(6.1\ifmmode\pm\else\textpm\fi{}1.8)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}13}$

{\mathrm{cm}}^{3}

${\mathrm{sec}}^{\mathrm{\ensuremath{-}}1}$. The experimental arrangement also permits absolute calibration of earlier crossed-beam measurements of the excitation function (cross section versus velocity) at conventional thermal beam kinetic energies. Present results together with earlier work show that the cross-sectional temperature dependence is in qualitative accord with theory.

We report cross-section measurements of the associative-ionization process, Na(3

{\mathit{p}}^{2}

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

)+Na(3

{\mathit{p}}^{2}

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

)\ensuremath{\rightarrow}

{\mathrm{Na}}_{2}^{+}

+e as a function of velocity, alignment, and orientation in the collision energy range from 300 to 5 K. Two independently tunable laser beams select narrow velocity classes of excited sodium in a well-collimated atomic beam. Circular and linear polarization of the excitation lasers permits alignment and orientation of the excited atoms in the two velocity classes. The excitation functions show pronounced differences reflecting different molecular pathways to the final product, and they bridge the energy range between conventional and ``cold'' collision dynamics.

{\mathrm{Na}}_{2}

states contributing to the AI process.