Journal of Physics B Atomic Molecular and Optical Physics

Excitation transfer from 31P, 31D to 33D of neutral helium by atomic collisions in a magnetic field: extension to higher magnetic fields

S Matsumoto, Ken-ichiro Shiozawa, T. Fujimoto

Published Jul 14, 1989• 1 citation

Abstract

The authors have extended their observation of the excitation transfer process to magnetic fields up to 10 T, which is higher than the value of 7.3 T at which the magnetic substates belonging to the 3 1 D and 3 3 D levels undergo level anticrossings. It is found that, with an increase in the magnetic field strength starting from zero, both the rate coefficients for excitation transfer 3 1 P to 3 3 D and 3 1 D to 3 3 D increase and then decrease. These dependences are almost exactly proportional to the magnetic-field dependence of the degree of mixing of the spin wavefunctions of the 3 1 D and 3 3 D levels.

DOI: 10.1088/0953-4075/22/13/005

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Publisher

Abstract

DOI: 10.1088/0953-4075/22/13/005

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An experimental study of excitation transfer between certain Zeeman sublevels of the

3^{2}P_{J}

states in strong magnetic fields is reported for $\mathrm{Na}(3^{2}S_{\frac{1}{2}})\ensuremath{-}{\mathrm{Na}}^{*}(3^{2}P_{J})$ resonant collisions. A major decrease in the $M=\ensuremath{-}\frac{3}{2}\ensuremath{\rightarrow}M=\frac{3}{2}$ transfer rate is observed between 4 and 80 kG. Approximate calculations in the correlation-function framework are performed, and the experimental results and theoretical predictions for the field dependence are in good agreement. Some insights into the mechanisms of the collision process are deduced and the particularly important role of the electronic spin is emphasized. The importance of the symmetry properties of the interaction potential is also directly demonstrated.

Transitions between the Zeeman substates of Cs 6

^{2}\mathrm{P}_{1/2}

and Rb 5

^{2}

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

atoms, induced in collisions with He atoms, have been investigated experimentally by methods of atomic fluorescence spectroscopy. The collision process has also been studied theoretically with time-dependent perturbation theory. Cs or Rb vapor contained in a quartz cell together with helium at low pressure was selectively excited by pulsed dye-laser radiation to the

^{2}

${\mathit{P}}_{1/2,\mathrm{\ensuremath{-}}1/2}$ Zeeman substate in a magnetic field ranging from 1.5 T to 7 T. The fluorescence spectrum, consisting of components emitted from the directly excited state and from the collisionally populated state, was resolved with a Fabry-P\'erot interferometer. Measurements of the relative intensities of the fluorescence components yielded the Zeeman mixing cross section for Cs-He and Rb-He collisions. It was found that the Cs 6

^{2}

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

cross section varied approximately as

{\mathit{B}}^{2}

in the range 0B0.76 T, showed a much weaker field dependence in the range from 0.76 T to 5 T, where it peaked, and declined slightly at B>5 T. The Rb 5

^{2}

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

cross section did not exhibit any variation with B. A theoretical calculation of the Cs cross section carried out using time-dependent perturbation theory explains the magnetic-field enhancement in terms of the minute magnetic-field-induced mixing of the

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

and

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

states and the resulting breaking of time-reversal symmetry. The results of the calculation are in good agreement with the experimental results at fields in the range 0B5 T.

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\\rm 6\\sp2P\\sb{1/2}

atoms in collisions with He atoms have been investigated by methods of atomic fluorescence spectroscopy. Cs vapour contained in a quartz cell together with helium at low pressure, was selectively excited by pulsed dye-laser radiation to the

\\rm 6\\sp2P\\sb{1/2,-1/2}

Zeeman substate in a magnetic field of strength ranging from 1.5 T to 7 T. The fluorescence spectrum consisting of components emitted from the directly excited state and from the collisionally populated state, was resolved with a Fabry-Perot interferometer. Measurements of the relative intensities of the fluorescence components yielded the Zeeman mixing cross section for Cs-He collisions. It was found that the enhancement in the cross section varied as B

\\sp2

in the range 0 $$ 5 T. A theoretical calculation of the magnetic-field enhancement of the cross section was also carried out, using time-dependent perturbation theory. The results of the calculation are in very good agreement with the experimental results at fields in the range 0

<

<

5 T, though not beyond 5 T where further theoretical work remains to be done.Dept. of Physics. Paper copy at Leddy Library: Theses & Major Papers - Basement, West Bldg. / Call Number: Thesis1993 .G365. Source: Masters Abstracts International, Volume: 32-02, page: 0636. Adviser: L. Krause. Thesis (M.Sc.)--University of Windsor (Canada), 1993.