Physical Review A

Velocity-selected atomic-beam collisions in the energy range from 300 to 5 K

Yinde Wang, J. Weiner

Published Jul 1, 1990• 13 citations

Abstract

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.

DOI: 10.1103/physreva.42.675

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Cold collisions in an atomic beam

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Physical Review AMar 1, 199025 citations

Spin-selected velocity dependence of the associative ionization cross section in Na(3p)+Na(3p) collisions over the collision energy range from 2.4 to 290 meV

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Physical Review A

Velocity-selected atomic-beam collisions in the energy range from 300 to 5 K

Yinde Wang, J. Weiner

Published Jul 1, 1990• 13 citations

Publisher

Abstract

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.

DOI: 10.1103/physreva.42.675

Related papers

Cold collisions in an atomic beam

H. R. Thorsheim, Yanping Wang, J. Weiner

We report a measurement of the rate constant for associative ionization (AI) between excited Na(3p) atoms colliding within a single beam at a velocity of 11.9 ${\mathrm{msec}}^{\mathrm{\ensuremath{-}}1}$, corresponding to a temperature of 65 mK. The collisions take place in a narrow velocity class of excited atoms produced by crossing the collimated Na beam with a monomode dye laser at an angle of 45\ifmmode^\circ\else\textdegree\fi{}. Light polarized linearly in the collision plane yields an AI rate constant greater than that for circular polarization by a factor of 2. We find ${K}_{65\mathrm{m}\mathrm{K}{}^{\mathrm{lin}}}$ =(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 a measurement of the rate constant for associative ionization (AI) between excited Na(3p) atoms colliding within a single beam at a velocity of 11.9 ${\mathrm{msec}}^{\mathrm{\ensuremath{-}}1}$, corresponding to a temperature of 65 mK. The collisions take place in a narrow velocity class of excited atoms produced by crossing the collimated Na beam with a monomode dye laser at an angle of 45\ifmmode^\circ\else\textdegree\fi{}. Light polarized linearly in the collision plane yields an AI rate constant greater than that for circular polarization by a factor of 2. We find ${K}_{65\mathrm{m}\mathrm{K}{}^{\mathrm{lin}}}$ =(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.

Physical Review AMar 1, 199025 citations

Spin-selected velocity dependence of the associative ionization cross section in Na(3p)+Na(3p) collisions over the collision energy range from 2.4 to 290 meV

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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

Ultracold photoassociative ionization collisions in an atomic beam: Optical field intensity and polarization dependence of the rate constant

Chun-Cheng Tsao, Reginaldo de Jesus Napolitano, Yang Wang +1 more

We report here measurements of two-body photoassociative ionization collisions between sodium atoms within an ultranarrow velocity class selected from a well-collimated, thermal atomic beam. Doppler-shifted excitation of the Na(3s ${\mathrm{}}^{2}$ ${\mathit{S}}_{1/2}$ ;F=1)\ensuremath{\rightarrow}Na(5p ${\mathrm{}}^{2}$ ${\mathit{P}}_{3/2}$ ) transition at 285 nm by a single-mode laser defines the narrow velocity class that subsequently populates the F=2 hyperfine level of the Na ground state by optical pumping. Probe laser beam excitation tuned near the Na(3s ${\mathrm{}}^{2}$ ${\mathit{S}}_{1/2}$ ;F=2)\ensuremath{\rightarrow}Na(3p ${\mathrm{}}^{2}$ ${\mathit{P}}_{3/2}$ ;F=3) transition produced photoassociative ionization with an average collision energy ${\mathit{E}}_{\mathit{K}}$ corresponding to a temperature of 5.3 mK ( ${\mathit{E}}_{\mathit{K}}$ =3/2kT). We determine the rate constant for the process as a function of probe beam intensity and polarization.We report here measurements of two-body photoassociative ionization collisions between sodium atoms within an ultranarrow velocity class selected from a well-collimated, thermal atomic beam. Doppler-shifted excitation of the Na(3s${\mathrm{}}^{2}$${\mathit{S}}_{1/2}$;F=1)\ensuremath{\rightarrow}Na(5p${\mathrm{}}^{2}$${\mathit{P}}_{3/2}$) transition at 285 nm by a single-mode laser defines the narrow velocity class that subsequently populates the F=2 hyperfine level of the Na ground state by optical pumping. Probe laser beam excitation tuned near the Na(3s${\mathrm{}}^{2}$${\mathit{S}}_{1/2}$;F=2)\ensuremath{\rightarrow}Na(3p${\mathrm{}}^{2}$${\mathit{P}}_{3/2}$;F=3) transition produced photoassociative ionization with an average collision energy ${\mathit{E}}_{\mathit{K}}$ corresponding to a temperature of 5.3 mK (${\mathit{E}}_{\mathit{K}}$=3/2kT). We determine the rate constant for the process as a function of probe beam intensity and polarization.

Physical Review AJan 1, 199511 citations

Associative ionization in collisions between excited Na atoms in the and the states

Jan Jette Blange, G Aben, H. Rudolph +2 more

For the first time, associative ionization has been observed in an atomic beam of excited sodium atoms in both the and the state. Relative values for the partial cross sections were obtained specified according to the different magnetic substate combinations of the two fine-structure states. These were found to be comparable to those for associative ionization between two atoms. However, the effect of the excitation on the ion production rate was found to be considerable and to depend strongly on the relative polarizations of the laser beams producing the two populations due to the redistribution of the involved magnetic sublevels. The results indicate that the initial orientation of the electron spin S does not significantly influence the associative ionization reaction at the mean collision energy of 25 meV.For the first time, associative ionization has been observed in an atomic beam of excited sodium atoms in both the and the state. Relative values for the partial cross sections were obtained specified according to the different magnetic substate combinations of the two fine-structure states. These were found to be comparable to those for associative ionization between two atoms. However, the effect of the excitation on the ion production rate was found to be considerable and to depend strongly on the relative polarizations of the laser beams producing the two populations due to the redistribution of the involved magnetic sublevels. The results indicate that the initial orientation of the electron spin S does not significantly influence the associative ionization reaction at the mean collision energy of 25 meV.

Journal of Physics B Atomic Molecular and Optical PhysicsJun 28, 19972 citations

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.

Journal of Physics B Atomic Molecular and Optical PhysicsJun 28, 199219 citations

Polarization-dependent spectra in the photoassociative ionization of cold atoms in a bright sodium beam

Jaime Ramirez-Serrano, W. DeGraffenreid, J. Weiner

We report measurements of cold photoassociative ionization (PAI) spectra obtained from collisions within a slow, bright Na atomic beam. A high-brightness atom flux, obtained by optical cooling and focusing of the atom beam, permits a high degree of alignment and orientation of binary collisions with respect to the laboratory atom-beam axis. The results reveal features of PAI spectra not accessible in conventional magneto-optical trap studies. We take advantage of this high degree of alignment to selectively excite autoionizing doubly excited states of specific symmetry.We report measurements of cold photoassociative ionization (PAI) spectra obtained from collisions within a slow, bright Na atomic beam. A high-brightness atom flux, obtained by optical cooling and focusing of the atom beam, permits a high degree of alignment and orientation of binary collisions with respect to the laboratory atom-beam axis. The results reveal features of PAI spectra not accessible in conventional magneto-optical trap studies. We take advantage of this high degree of alignment to selectively excite autoionizing doubly excited states of specific symmetry.

Physical Review AMay 8, 20026 citations

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}^{+}

{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.

{\mathrm{Na}}_{2}

states contributing to the AI process.

{\mathrm{}}^{2}

{\mathit{S}}_{1/2}

;F=1)\ensuremath{\rightarrow}Na(5p

{\mathrm{}}^{2}

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

) transition at 285 nm by a single-mode laser defines the narrow velocity class that subsequently populates the F=2 hyperfine level of the Na ground state by optical pumping. Probe laser beam excitation tuned near the Na(3s

{\mathrm{}}^{2}

{\mathit{S}}_{1/2}

;F=2)\ensuremath{\rightarrow}Na(3p

{\mathrm{}}^{2}

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

;F=3) transition produced photoassociative ionization with an average collision energy

{\mathit{E}}_{\mathit{K}}

corresponding to a temperature of 5.3 mK (

{\mathit{E}}_{\mathit{K}}

=3/2kT). We determine the rate constant for the process as a function of probe beam intensity and polarization.