Physical Review A

Experimental measurements of field effects on dielectronic recombination cross sections and Rydberg product-state distributions

Alfred Müller, D. Belić, Brett D DePaola, Nada Djurić, G. H. Dunn, D. W. Mueller, C. Timmer

Published Jul 1, 1987• 78 citations

Abstract

Experimental details are presented for the measurement of the effects of extrinsic electric fields on cross sections and Rydberg product-state distributions for dielectronic recombination of ${\mathrm{Mg}}^{+}$ with electrons. A new type of Rydberg state detector is described. Experimental results for dielectronic recombination in the presence of fields are presented for three field values, and these results are compared with theoretical calculations.

DOI: 10.1103/physreva.36.599

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Physical Review A

Experimental measurements of field effects on dielectronic recombination cross sections and Rydberg product-state distributions

Alfred Müller, D. Belić, Brett D DePaola, Nada Djurić, G. H. Dunn, D. W. Mueller, C. Timmer

Published Jul 1, 1987• 78 citations

Publisher

Abstract

Experimental details are presented for the measurement of the effects of extrinsic electric fields on cross sections and Rydberg product-state distributions for dielectronic recombination of

{\mathrm{Mg}}^{+}

with electrons. A new type of Rydberg state detector is described. Experimental results for dielectronic recombination in the presence of fields are presented for three field values, and these results are compared with theoretical calculations.

DOI: 10.1103/physreva.36.599

Related papers

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Alfred Müller, D. Belić, Brett D DePaola +4 more

The effects of state mixing by extrinsic fields in the collision region have been investigated for the dielectronic recombination process ${\mathrm{Mg}}^{+}$ (3s)+e\ensuremath{\rightarrow}Mg(3p,nl)\ensuremath{\rightarrow}Mg(3s ,nl)+h\ensuremath{\nu}. By field ionization of the Rydberg atoms produced, cross sections \ensuremath{\sigma}( ${n}_{f}$ ) have been measured. The observed large changes of \ensuremath{\sigma}( ${n}_{f}$ ) with alteration of the extrinsic field provide the first incontrovertible experimental evidence that dielectronic recombination can be changed by external fields.The effects of state mixing by extrinsic fields in the collision region have been investigated for the dielectronic recombination process ${\mathrm{Mg}}^{+}$(3s)+e\ensuremath{\rightarrow}Mg(3p,nl)\ensuremath{\rightarrow}Mg(3s ,nl)+h\ensuremath{\nu}. By field ionization of the Rydberg atoms produced, cross sections \ensuremath{\sigma}(${n}_{f}$) have been measured. The observed large changes of \ensuremath{\sigma}(${n}_{f}$) with alteration of the extrinsic field provide the first incontrovertible experimental evidence that dielectronic recombination can be changed by external fields.

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Dielectronic recombination has been directly observed with a crossed, modulated electron and calciumion beams technique. The stabilizing photons (about 397 nm) and the 500-eV Rydberg-state neutral atoms were detected in coincidence following electron-impact excitation in the vicinity of doubly excited ${\mathrm{Ca}}^{**}$ resonant states below the ${\mathrm{Ca}}^{+}(4p^{2}P)$ excited ionic state. A peak ${\mathrm{Ca}}^{+}(4P^{2}P_{\frac{3}{2}})$ excitation cross section of 1.7 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}15}$ ${\mathrm{cm}}^{2}$ was measured simultaneously with the peak dielectronic recombination cross section of 1.8 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}17}$ ${\mathrm{cm}}^{2}$ which is about double the Burgess-Mertz theoretical value.Dielectronic recombination has been directly observed with a crossed, modulated electron and calciumion beams technique. The stabilizing photons (about 397 nm) and the 500-eV Rydberg-state neutral atoms were detected in coincidence following electron-impact excitation in the vicinity of doubly excited ${\mathrm{Ca}}^{**}$ resonant states below the ${\mathrm{Ca}}^{+}(4p^{2}P)$ excited ionic state. A peak ${\mathrm{Ca}}^{+}(4P^{2}P_{\frac{3}{2}})$ excitation cross section of 1.7 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}15}$ ${\mathrm{cm}}^{2}$ was measured simultaneously with the peak dielectronic recombination cross section of 1.8 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}17}$ ${\mathrm{cm}}^{2}$ which is about double the Burgess-Mertz theoretical value.

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Effects of electric fields on doubly excited autoionizing Rydberg states of barium

Kambiz Ali Safinya, J. F. Delpech, Thomas F. Gallagher

We report the effects of static electric fields on the doubly excited $6{p}_{\frac{1}{2}}\mathrm{nl}$ states of barium in the region ${n}^{*}=12$ . Using a three-step laser excitation scheme we have measured the electric-field dependence of the positions and autoionization widths of the $6{p}_{\frac{1}{2}}\ensuremath{-}17s,16p,15d,12l (l=4\ensuremath{-}10),12f, \mathrm{and} 16s$ states at field values of up to 4.92 kV/cm. The photoexcitation spectra of the autoionizing states exhibit interference effects which are well understood and provide a better understanding of the character of these states in electric fields. The systematic study of the spectra and positions allows us to explain the field dependence of the autoionization widths in terms of electric-field mixing of the discrete portions of the auoionizing states. The relationship of these effects to dielectronic recombination rates of ions and electrons in plasma microfields is discussed.We report the effects of static electric fields on the doubly excited $6{p}_{\frac{1}{2}}\mathrm{nl}$ states of barium in the region ${n}^{*}=12$. Using a three-step laser excitation scheme we have measured the electric-field dependence of the positions and autoionization widths of the $6{p}_{\frac{1}{2}}\ensuremath{-}17s,16p,15d,12l (l=4\ensuremath{-}10),12f, \mathrm{and} 16s$ states at field values of up to 4.92 kV/cm. The photoexcitation spectra of the autoionizing states exhibit interference effects which are well understood and provide a better understanding of the character of these states in electric fields. The systematic study of the spectra and positions allows us to explain the field dependence of the autoionization widths in terms of electric-field mixing of the discrete portions of the auoionizing states. The relationship of these effects to dielectronic recombination rates of ions and electrons in plasma microfields is discussed.

Physical Review ASep 1, 198020 citations

Enhancement of dielectronic recombination in crossed electric and magnetic fields

Victor Klimenko, Lung Ko, Thomas F. Gallagher

Dielectronic recombination (DR) from a continuum of finite bandwidth in Ba atoms has been studied in electric fields of 0--5 V/cm and magnetic fields of 0--240 G for both $\stackrel{\ensuremath{\rightarrow}}{B}\ensuremath{\parallel}\stackrel{\ensuremath{\rightarrow}}{E}$ and $\stackrel{\ensuremath{\rightarrow}}{B}\ensuremath{\perp}\stackrel{\ensuremath{\rightarrow}}{E}.$ In electric fields of \ensuremath{\geqslant}0.1 V/cm, the presence of a perpendicular magnetic field increases the integrated DR rate by up to 60%, with the peak enhancement moving towards higher magnetic fields as the electric field is increased. The general behavior of the enhancement for $\stackrel{\ensuremath{\rightarrow}}{B}\ensuremath{\perp}\stackrel{\ensuremath{\rightarrow}}{E}$---as well its absence for $\stackrel{\ensuremath{\rightarrow}}{B}\ensuremath{\parallel}\stackrel{\ensuremath{\rightarrow}}{E}$ is in agreement with theoretical expectations. A simple model is presented to provide insight into the results, and reasons for its shortcomings are presented.Dielectronic recombination (DR) from a continuum of finite bandwidth in Ba atoms has been studied in electric fields of 0--5 V/cm and magnetic fields of 0--240 G for both $\stackrel{\ensuremath{\rightarrow}}{B}\ensuremath{\parallel}\stackrel{\ensuremath{\rightarrow}}{E}$ and $\stackrel{\ensuremath{\rightarrow}}{B}\ensuremath{\perp}\stackrel{\ensuremath{\rightarrow}}{E}.$ In electric fields of \ensuremath{\geqslant}0.1 V/cm, the presence of a perpendicular magnetic field increases the integrated DR rate by up to 60%, with the peak enhancement moving towards higher magnetic fields as the electric field is increased. The general behavior of the enhancement for $\stackrel{\ensuremath{\rightarrow}}{B}\ensuremath{\perp}\stackrel{\ensuremath{\rightarrow}}{E}$---as well its absence for $\stackrel{\ensuremath{\rightarrow}}{B}\ensuremath{\parallel}\stackrel{\ensuremath{\rightarrow}}{E}$ is in agreement with theoretical expectations. A simple model is presented to provide insight into the results, and reasons for its shortcomings are presented.

Physical Review AJul 30, 20032 citations

Experimental details are presented for the measurement of the effects of extrinsic electric fields on cross sections and Rydberg product-state distributions for dielectronic recombination of

{\mathrm{Mg}}^{+}

The effects of state mixing by extrinsic fields in the collision region have been investigated for the dielectronic recombination process

{\mathrm{Mg}}^{+}

(3s)+e\ensuremath{\rightarrow}Mg(3p,nl)\ensuremath{\rightarrow}Mg(3s ,nl)+h\ensuremath{\nu}. By field ionization of the Rydberg atoms produced, cross sections \ensuremath{\sigma}(

{n}_{f}

) have been measured. The observed large changes of \ensuremath{\sigma}(

{n}_{f}

) with alteration of the extrinsic field provide the first incontrovertible experimental evidence that dielectronic recombination can be changed by external fields.

{\mathrm{Ca}}^{**}

resonant states below the

{\mathrm{Ca}}^{+}(4p^{2}P)

excited ionic state. A peak

{\mathrm{Ca}}^{+}(4P^{2}P_{\frac{3}{2}})

excitation cross section of 1.7 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}15}$

{\mathrm{cm}}^{2}

was measured simultaneously with the peak dielectronic recombination cross section of 1.8 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}17}$

{\mathrm{cm}}^{2}

which is about double the Burgess-Mertz theoretical value.

We report the effects of static electric fields on the doubly excited

6{p}_{\frac{1}{2}}\mathrm{nl}

states of barium in the region

{n}^{*}=12

. Using a three-step laser excitation scheme we have measured the electric-field dependence of the positions and autoionization widths of the $6{p}_{\frac{1}{2}}\ensuremath{-}17s,16p,15d,12l (l=4\ensuremath{-}10),12f, \mathrm{and} 16s$ states at field values of up to 4.92 kV/cm. The photoexcitation spectra of the autoionizing states exhibit interference effects which are well understood and provide a better understanding of the character of these states in electric fields. The systematic study of the spectra and positions allows us to explain the field dependence of the autoionization widths in terms of electric-field mixing of the discrete portions of the auoionizing states. The relationship of these effects to dielectronic recombination rates of ions and electrons in plasma microfields is discussed.