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Journal of Physics B Atomic Molecular and Optical Physics

Na-Cs Hornbeck-Molnar ionization

C. Gabbanini, M Biagini, Silvia Gozzini, A. Lucchesini, L. Moi

Published Sep 14, 1991• 5 citations
Publisher

Abstract

An investigation of the 'Hornbeck-Molnar ionization' process between laser-excited Cs and ground state Na atoms has been performed in a crossed beam apparatus. Caesium atoms in the 8d, 10s, 9d, 11s and 10d levels respectively have been obtained by two-step resonant CW laser excitation. The relative collisional cross sections and the dissociation energy of the NaCs + molecular ion have been obtained from quantitative analysis of the produced atomic and molecular ions. The experimental results are compared with the theoretical values calculated using a model developed by Janev and Mihajlov (1980).

DOI
10.1088/0953-4075/24/17/016

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Cesium molecules are pumped by a CW dye laser. Some of the excited molecules then pre-dissociate or collisionally transfer excitation to produce excited atoms at the 5D and 6P levels. The cross sections (in units of 10-14cm2) for the excitation transfer process Cs(6P)+Cs(5D) →Cs(7DJ)+Cs(6S)for J being 5/2 and 3/2 are 5. 4 ± 50% and 4. 9 ± 50%, respectively. The cross sections (in units of 10-14cm2) for the excitation transfer out of the 7D doublet [i. e. , Cs(7DJ)+Cs(6S) →states other than Cs(7D)] for J being 5/2 and 3/2 are 1. 6 ±50% and 0. 34±50%, respectively. To obtain these cross sections, the intensities of 7D and 5D fluorescence emissions and the 6P atom density are measured by using the absorption equivalent width technique. The results are discussed in eomparison with those of other experiments.

Acta Physica Sinica•Jan 1, 1993•1 citation
An investigation of the 'Hornbeck-Molnar ionization' process between laser-excited Cs and ground state Na atoms has been performed in a crossed beam apparatus. Caesium atoms in the 8d, 10s, 9d, 11s and 10d levels respectively have been obtained by two-step resonant CW laser excitation. The relative collisional cross sections and the dissociation energy of the NaCs + molecular ion have been obtained from quantitative analysis of the produced atomic and molecular ions. The experimental results are compared with the theoretical values calculated using a model developed by Janev and Mihajlov (1980).
Rb + and Rb 2 + formation in a laser-excited Rb vapour is extensively studied for s and d levels ranging from 5d to 11s levels. Collisional ionisation with a ground-state atom leads to Rb 2 + formation by Hornbeck-Molnar reaction with rate coefficients lying in the 10 -10 cm 3 s -1 range. This reaction is analysed theoretically. Penning ionisation occurs in collision with a resonant-state atom, Rb(5p), with a high efficiency (rate coefficient above 10 -8 cm 3 s -1 ). Associative ionisation between the 7s level and the 5p level is also observed (rate coefficient about 10 -10 cm 3 s -1 ). This reaction appears negligible for the neighbouring 5d level.
In studying ionization reactions in a single dense effusive beam of laser-excited Na(3p) atoms, we observe production of both Na{sub 2}{sup +} and Na{sup +} ions. The Na{sup +} results from the familiar associative ionization reaction of two Na(3p) atoms and the Na{sup +} ions under our conditions result mostly from the collisional dissociation of the Na{sub 2}{sup +} by reaction with a third excited Na(3p) atom, rather than from photo- dissociation or photoionization. A CW, single-frequency dye laser tuned to 589 nm resonantly excites the Na(3s) atoms to the 3p state. The atomic beam Na(3s) density is determined from low-intensity 589 absorption measurements. Na{sup +} ion yield depends on the cube of the Na beam density, suggesting successive collisions of three Na(3p) atoms: we believe the Na{sub 2}{sup +} ions polarize the third Na(3p) atom, resulting in a R{sup -4} orbiting collision interaction. A large collisional dissociation cross-section of approximately (4{plus_minus}2)x10{sup -13} cm{sup 2} results, for oven temperatures in the 500-600K range.
Using stepwise excitation of the cesium 8S atoms level in Cs vapor,several collisional and radiative processes have been identified from the intensities and spectra of the Cs fluorescence.The 5D state was populated by 8S→7P→5D transitions.In cesium densities 1016-1017?cm-3,the energy pooling collisions 5D+5D→nL+6S(nL=9D,11S,7F are studied.Since the 5D→6P(3.0-3.6 μm) fluorescence could not be detected with this experiment,the EP rate coefficients have been measured relative to the known rate coefficient of the collision,i.e.,6P+5D→6S+7D.The excited-atom density and spatial distribution were mapped by monitoring the absorption of a counterpropagating single-mode laser beam,tuned to 6P3/2→8S1/2 transition,which could be translated parallel to the pump beam.The excited atom densities are combined with measured fluorescene ratios to determine cross sections for the cesium energy pooling process.The average values(in units of 10-10?cm3s-1) for nL=9D,11S and 7F are 8.4±4.2,7.3±3.6,and 9.7±4.8,respectively.Influence on k11S and k7F of the energy transfer process 11S+6S7F+6S is also dicussed.
The results of an experiment on the associative ionization collision between sodium and cesium excited atoms are reported. The atoms are excited by two resonant cw lasers to the 3P3/2{\mathit{P}}_{3/2}P3/2​ and 6P3/2{\mathit{P}}_{3/2}P3/2​ levels, respectively, and the formation of the NaCs+{\mathrm{NaCs}}^{+}NaCs+ molecular ion is observed. The rate constant of such process has been measured relative to the known rate constant of sodium associative ionization and its value resulted in K=(5.4\ifmmode\pm\else\textpm\fi{}3.2)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}11}$ cm3{\mathrm{cm}}^{3}cm3 ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$.
Cesium molecules are pumped by a CW dye laser. Some of the excited molecules then pre-dissociate or collisionally transfer excitation to produce excited atoms at the 5D and 6P levels. The cross sections (in units of 10-14cm2) for the excitation transfer process Cs(6P)+Cs(5D) →Cs(7DJ)+Cs(6S)for J being 5/2 and 3/2 are 5. 4 ± 50% and 4. 9 ± 50%, respectively. The cross sections (in units of 10-14cm2) for the excitation transfer out of the 7D doublet [i. e. , Cs(7DJ)+Cs(6S) →states other than Cs(7D)] for J being 5/2 and 3/2 are 1. 6 ±50% and 0. 34±50%, respectively. To obtain these cross sections, the intensities of 7D and 5D fluorescence emissions and the 6P atom density are measured by using the absorption equivalent width technique. The results are discussed in eomparison with those of other experiments.