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Journal of Physics B Atomic Molecular and Optical Physics

Differential cross sections for radiation assisted collisions between atoms

Joachim Großer, D Hohmeier, Selina Klose

Published Jan 28, 1996• 9 citations
Publisher

Abstract

We report angle resolved measurements of the excited Na atoms from the process with non-resonant light. The experiment provides a method to probe the NaKr collision pair by a photon. The Na( ) angular distribution shows an oscillatory structure, which can be used for a test of the NaKr potential curve system. The signal depends strongly upon the polarization of the photon. The effect provides information about the geometric properties of the collision pair.

DOI
10.1088/0953-4075/29/2/017

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We report angle resolved measurements of the excited Na atoms from the process with non-resonant light. The experiment provides a method to probe the NaKr collision pair by a photon. The Na( ) angular distribution shows an oscillatory structure, which can be used for a test of the NaKr potential curve system. The signal depends strongly upon the polarization of the photon. The effect provides information about the geometric properties of the collision pair.
We measured the angular distribution of the excited Na atoms from the process Na(Ss)+Kr+h nu to Na(3p)+Kr. The photon energy is detuned by 50 cm -1 from the Na resonance energy and the optical transition can occur only when the atoms are close to each other. The angular resolution allows the observation only of the general structure of the cross section, but not of finer details. We describe the experimental method and the experimental difficulties, especially the origin of a number of competing signals. We discuss the process as a new way of observing the collision Na+Kr, using the photon as a probe.
The optical collision Na(3s)+Kr+hν→Na(3p)+Kr has been investigated in an experiment with crossed atomic beams and with a differential detection of the excited collision products. Three groups of experimental results have been obtained, which all demonstrate unprecedented possibilities for the observation of atomic collisions. 1. The oscillatory structure of the differential cross sections allows a sensitive test of the molecular potentials. 2. Polarization experiments give direct information about the geometric characteristics of the collision complex. 3. State analysis of the collision products provides a tool for the observation of elementary nonadiabatic processes. A number of possible future experiments, which make use of the new ideas, is discussed, in addition.
Optical collisions in a crossed beam experiment are examined for the atomic collision pairs LiHe, LiNe, NaNe.Differential cross sections are measured in order to probe the quallity of quantum chemical calculated and spectroscopical determined molecular potentials.The linear polarization of the excitation laser is used to manipulate the contrast of the differential cross sections for NaNe.Using elliptical polarized light total control over the angular position and the contrast of the interference pattern is demonstrated.Differential cross sections for the collision pairs LiH and LiD show a pronounced oscillatory structure, which for the first time is observed for atom-molecule optical collisions.
We study the laser excitation of atomic collision pairs in a differential scattering experiment. The interference structure in the differential cross-section is resolved and shows a considerable variation with the linear polarization of the laser light. A systematic analysis allows the accurate determination of the Condon vectors characterizing the optical transition. The method is thus capable to directly visualize geometric aspects of the collision event, very much like an everyday photography.
The cross sections for the excitation energy transfer in the collisional processes Na*(3P 1 2/)+M(nS 1 2/) to or from Na*(3p 3 2/)+m(Ns 3 2/), m being ground-state Rb (n=5) or Cs (n=6) atom, have been measured by laser fluorescence method. With either of the two sodium 3P fine-structure states optically excited, the intensity ratio of the sensitized to direct fluorescence was measured. The polarization effects due to partially polarized and anisotropic direct fluorescence were investigated. The measured cross sections (T=530 K) for the sodium 3P fine-structure excitation transfer induced by collisions with Rb are: sigma ( 1 / 2 to 3 / 2 )=170 AA 2 , with an overall accuracy of 20%. The corresponding values in the Cs case are: sigma ( 1 / 2 to 3 / 2 )=140 AA 2 , sigma ( 3 / 2 to 1 / 2 )=83 AA 2 . The theoretical calculations reveal the decisive role of the dipole-quadrupole interaction. The obtained values are in satisfactory agreement with the experiment only if both the dipole-dipole and dipole-quadrupole interactions are taken into account, while the calculations involving the dipole-dipole term alone yield the cross section values which are as much as one order of magnitude lower than the experimentally observed ones.