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Journal of Physics B Atomic Molecular and Optical Physics

Energy pooling reactions between two Na* (3p) atoms specified according to magnetic substate combinations

J H Nijland, Jan Jette Blange, H. Rudolph, H.A. Dijkerman, H G M Heideman

Published Nov 28, 1992• 10 citations
Publisher

Abstract

In a beam experiment the authors have studied the energy pooling reaction between two laser excited Na* (3p) atoms, where in the final state one of the sodium atoms is in the 5s or 4d state and the other in the ground state. They have determined all eight independent partial cross sections and coherence terms, specified according to the various magnetic substate combinations of the colliding Na* (3p) atoms, as a function of the collision velocity. This is the maximum information that can be extracted from the experiment given the symmetry of the detection scheme. By applying a weak magnetic field, to orient the Na* (3p) atoms, the authors were able to distinguish between the two partial cross sections sigma 11 and sigma 1-1 , where the subscripts 11 and 1-1 refer to the initial magnetic substate combinations of the two collision partners. By using an electro-optical modulator the authors have furthermore improved the signal-to-noise ratio to an extent where it was possible to measure all coherence terms.

DOI
10.1088/0953-4075/25/22/018

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•Feb 1, 1997•0 citations
In a beam experiment the authors have studied the energy pooling reaction between two laser excited Na* (3p) atoms, where in the final state one of the sodium atoms is in the 5s or 4d state and the other in the ground state. They have determined all eight independent partial cross sections and coherence terms, specified according to the various magnetic substate combinations of the colliding Na* (3p) atoms, as a function of the collision velocity. This is the maximum information that can be extracted from the experiment given the symmetry of the detection scheme. By applying a weak magnetic field, to orient the Na* (3p) atoms, the authors were able to distinguish between the two partial cross sections sigma 11 and sigma 1-1 , where the subscripts 11 and 1-1 refer to the initial magnetic substate combinations of the two collision partners. By using an electro-optical modulator the authors have furthermore improved the signal-to-noise ratio to an extent where it was possible to measure all coherence terms.
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 Na atom is in the 5s or 4d state and the other in the ground state. They have found that this reaction is strongly dependent on the polarization of the laser light used to prepare the Na*(3p) atoms. An analysis of theoretical potential curves suggests that the reaction mainly proceeds via the input channel where one of the atoms is in the M=0 and the other in the M=1 substate. Their experimental results are in qualitative agreement with that suggestion.
Cross sections sigma (m 1 m 2 ) nl for the energy pooling processes in the collision between two excited sodium atoms are calculated for the case when the partners are prepared in the 3p-excited states with the definite orbital momentum projections m 1 and m 2 . As a result of the process one of the colliding atoms comes to the ground state and the other partner is excited to nl state with nl=5s, 4d, 4f. The collision velocity is equal to or higher than thermal. The Landau-Zener-locking model (LZ-locking) is developed: the sudden change of the type of the coupling between the electron orbital momentum and the internuclear axis (the locking approximation) is combined with the multicrossing Landau-Zener model. The validity of the LZ-locking model is analysed. The results show strong cross section dependence on the initial quantum numbers m 1 and m 2 , especially in the 5s channel.
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.
We report our measurements of the cross sections ${\ensuremath{\sigma}}_{5S}$ and ${\ensuremath{\sigma}}_{4D}$ for the electronic-energy-transfer process $\mathrm{Na}(3P)+\mathrm{Na}(3P)\ensuremath{\rightarrow}\mathrm{Na}(5S,4D)+\mathrm{Na}(3S)$. To obtain these cross sections we have measured the fluorescence intensity for the transitions $5S\ensuremath{\rightarrow}3P$, $4D\ensuremath{\rightarrow}3P$, and $3P\ensuremath{\rightarrow}3S$ in sodium vapor excited with a cw dye laser. The study of this electronic energy transfer is complicated and there is a large disagreement (\ensuremath{\gtrsim}104{10}^{4}104) among reported measurements. We believe we have avoided most of the difficulties of previous experiments. Our results are ${\ensuremath{\sigma}}_{5S}=(2.0\ifmmode\pm\else\textpm\fi{}0.7)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}15}$ cm2{\mathrm{cm}}^{2}cm2 and ${\ensuremath{\sigma}}_{4D}=(3.2\ifmmode\pm\else\textpm\fi{}1.1)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}15}$ ${\mathrm{cm}}^{\ensuremath{-}2}$, and they are compared with the results of other experiments.
Two different atomic species, sodium and potassium, are resonantly excited in a ceel by a CW dye laser and a potassium lamp, respectively. The density of the excited Na (3P) atoms in the cell is measured directly using the absorption-equivalent-width technique on the lines of the diffuse series. To isolate the heteronuclear contribution in the fluorescence spectrum, a modulation detection technique is adopted. The energy-pooling collisions between Na (3P) and K (4P) are observed and cross sections are obtained.