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Physical Review Letters

Fine-Structure Transition in Ne( P03 ) on Ne( S01 ) Collisions at Thermal Energies

I. Colomb de Daunant, G. Vassilev, M. Dumont, J. Baudon

Published May 18, 1981• 13 citations
Publisher

Abstract

The collision-induced exothermic fine-structure transition $\mathrm{Ne}(^{3}P_{0})\ensuremath{-}\mathrm{Ne}(^{3}P_{2})$ has been observed in a crossed-effusive-beam experiment, by measuring the time of flight of metastable atoms scattered perpendicularly to the incident-beam plane. In this direction, the elastic scattering is kinematically discriminated. The identification of the transition is achieved by pumping $^{3}P_{0}$ or $^{3}P_{2}$ levels with a cw dye laser.

DOI
10.1103/physrevlett.46.1322

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The collision-induced exothermic fine-structure transition Ne(3P0)\ensuremath−Ne(3P2)\mathrm{Ne}(^{3}P_{0})\ensuremath{-}\mathrm{Ne}(^{3}P_{2})Ne(3P0​)\ensuremath−Ne(3P2​) has been observed in a crossed-effusive-beam experiment, by measuring the time of flight of metastable atoms scattered perpendicularly to the incident-beam plane. In this direction, the elastic scattering is kinematically discriminated. The identification of the transition is achieved by pumping 3P0^{3}P_{0}3P0​ or 3P2^{3}P_{2}3P2​ levels with a cw dye laser.
Absolute velocity-resolved total integral cross sections have been measured for collisions of helium singlet (2 1 S 0 ) and triplet (2 3 S 1 2) metastable (He*) atoms with ground-state helium, neon, and argon atoms in the thermal velocity range of 1.0-3.5*10 5 cm s -1 . Additional measurements on the He*-Ne system with a large input aperture at the detector to suppress the sensitivity of the apparatus to elastic scattering failed to show the previously predicted (Arathoon) sharply rising velocity structure in the inelastic excitation transfer cross sections.
Laser spectroscopy has been performed on a beam of neutral 4He^{4}\mathrm{He}4He atoms. By using transverse laser cooling and focusing, we are able to prepare a bright beam of atoms in the metastable state 23S12\phantom{\rule{0.16em}{0ex}}{}^{3}{S}_{1}23S1​ deflected from the original effusive atomic beam. The initial state preparation is completed with optical pumping on the $2\phantom{\rule{0.16em}{0ex}}{}^{3}{P}_{1}\ensuremath{\leftarrow}2\phantom{\rule{0.16em}{0ex}}{}^{3}{S}_{1}$ transition at the wavelength of 1083 nm, followed by laser spectroscopy on the $2\phantom{\rule{0.16em}{0ex}}{}^{3}{P}_{1,2}\ensuremath{\leftarrow}2\phantom{\rule{0.16em}{0ex}}{}^{3}{S}_{1}$ transitions. The $2\phantom{\rule{0.16em}{0ex}}{}^{3}{P}_{1}\ensuremath{-}2\phantom{\rule{0.16em}{0ex}}{}^{3}{P}_{2}$ fine-structure splitting is determined to be $2\phantom{\rule{0.16em}{0ex}}291\phantom{\rule{0.16em}{0ex}}177.69\ifmmode\pm\else\textpm\fi{}0.36\phantom{\rule{0.16em}{0ex}}\mathrm{kHz}$. The quantum interference effect is included in data extraction. This is the most precise laser spectroscopy measurement of the interval. Our result is in agreement with both the latest QED-based calculation and the most precise measurement conducted with microwave spectroscopy.
The cross section for the transfer of excitation from the 23P02^{3}P_{0}23P0​ level of helium to the 23P12^{3}P_{1}23P1​ and 23P22^{3}P_{2}23P2​ levels as a result of collisions with the ground-state helium atom (11S01^{1}S_{0}11S0​) has been measured with a conventional resonance-fluorescence technique. A He4{\mathrm{He}}^{4}He4 source excited the $2^{3}S_{1}\ensuremath{-}2^{3}P_{0}$ transition in a He3{\mathrm{He}}^{3}He3 absorption cell. The scattered light was examined with a high-resolution grating spectrometer and the ratio of the $2^{3}P_{0}\ensuremath{\rightarrow}2^{3}S_{1}$ to the $2^{3}P_{1,2}\ensuremath{\rightarrow}2^{3}S_{1}$ intensities was measured as a function of cell pressure from 0.05 to 10 Torr. The cross section for collision-induced transitions out of the 23P02^{3}P_{0}23P0​ level is found to be (68\ifmmode\pm\else\textpm\fi{}3) \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}16}$ cm2{\mathrm{cm}}^{2}cm2 at room temperature.
Electron scattering by excited sodium atoms has been carried out in a crossed-beam experiment. The atoms have been optically pumped into a well defined hyperfine level (3 2 P 3 2/F=3) by a tunable CW dye laser. For two of the most prominent scattering processes, the 3 2 P to 3 2 S and 3 2 P to 4 2 S transitions, the effect of the anisotropy of the initial state introduced by the laser light is studied in detail and is interpreted in terms of multipole moments describing the optical excitation and the collision process. Possibilities and limitations of the experiment are discussed. Electron collisions may be seen as a test case for the understanding of more involved interaction processes.
Collision kernels describing elastic collision effects in saturation spectroscopy are completely calculated for the metastable 3P0^{3}P_{0}3P0​ state of neon, starting from true experiment-deduced potentials. Collision processes with and without metastability exchange are respectively considered. A direct observation of these two kernels is provided by a two-laser time-resolved saturated absorption experiment. They are in good agreement with theory.
Intramultiplet mixing collisions have been investigated using polarized Ne(3p)\mathrm{Ne}(3p)Ne(3p) atoms with a well-defined initial relative velocity, i.e., two initial-state vectors. By analyzing the final-state center-of-mass velocity with a (Doppler-detuned) probe laser with a well-defined polarization and detecting the laser-induced fluorescence we measure the differential cross section and the polarization of the final state, i.e., two final-state vectors. Measurements have been done at a collision energy E=70meV,E=70\mathrm{meV},E=70meV, for both the ${\ensuremath{\alpha}}_{7}$ and ${\ensuremath{\alpha}}_{9}$ (Paschen numbering) initial states. For the elastic ${\ensuremath{\alpha}}_{7}\ensuremath{\rightarrow}{\ensuremath{\alpha}}_{7}$ collisions the experimental results are strongly hindered by the undesired response on elastic scattering of the metastable Ne(3s,3P0)\mathrm{Ne}{(3s,}^{3}{P}_{0})Ne(3s,3P0​) state. Inelastic collisions have been investigated for the ${\ensuremath{\alpha}}_{9}$ state, that forms a closed level system with the metastable Ne(3s,3P2)\mathrm{Ne}{(3s,}^{3}{P}_{2})Ne(3s,3P2​) state. For the ${\ensuremath{\alpha}}_{9}\ensuremath{\rightarrow}{\ensuremath{\alpha}}_{8}$ transition experimental results are presented for both parallel and perpendicular orientations of the polarizations of the pump and probe laser, respectively, as well as for circular polarized $({\ensuremath{\sigma}}^{+},{\ensuremath{\sigma}}^{+})$ and $({\ensuremath{\sigma}}^{+},{\ensuremath{\sigma}}^{\ensuremath{-}})$ configurations. The experiments are compared to a full quantum-mechanical coupled channels calculation of the scattering process, using the model potentials of Hennecart and Masnou-Seeuws as input. The output of this calculation is combined with a density matrix description of the initial- and final-state polarization. Both shape of the differential cross sections and their relative scaling for different laser polarizarion configurations agree well with experiment. This gives strong support for the quality of the model potentials used.