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Applied Optics

Collisional Excitation Transfer Between the P2_12 and P2_32 Levels in Alkali Atoms

L. Krause

Published Sep 1, 1966• 128 citations
Publisher

Abstract

An account of recent work is given by the author and co-workers on the experimental determination of cross sections for excitation transfer between the (2)P((1/2)) and (2)P(3/2)resonance levels in potassium, rubidium and cesium, induced by inelastic collisions with alkali atoms and inert gas atoms in their ground states. Forty values of cross sections were obtained in a series of sensitized fluorescence experiments, in which alkali vapors and vapor-gas mixtures were irradiated with one component of the appropriate alkali resonance doublet, and the relative intensities of both components appearing in the fluorescent light were measured. The experiments indicate that the collisional interaction between an alkali atom in a (2)P state and a ground state inert gas atom probably occurs between the inert gas atom and the (2)P alkali valence electron which behaves like a quasi-free particle.

DOI
10.1364/ao.5.001375

Related papers

Inelastic Collisions between Excited Alkali Atoms and Molecules. I. Sensitized Fluorescence and Quenching in Cs- N2 and Cs- H2 Systems

D. A. McGillis, L. Krause

Excitation transfer between the $6 ^{2}P_{\frac{1}{2}}$ and $6 ^{2}P_{\frac{3}{2}}$ resonance states in cesium, induced by Cs-${\mathrm{N}}_{2}$ and Cs-${\mathrm{H}}_{2}$ collisions, was observed in the first experiment of its kind, in which techniques of sensitized fluorescence are used to investigate collisional mixing between resonance states of alkali atoms in mixtures with molecular gases. The cesium-vapor-gas system, in which the cesium vapor pressure was low enough to avoid radiation trapping, was irradiated with a single component of the resonance doublet. The fluorescent light, which contained both components of the doublet, was monitored at right angles to the direction of excitation. Measurements of relative intensities of the fluorescent components yielded the following cross sections for excitation transfer and for quenching of resonance radiation. For Cs-${\mathrm{N}}_{2}$ collisions: ${Q}_{12}(^{2}P_{\frac{1}{2}}\ensuremath{\rightarrow}^{2}P_{\frac{3}{2}})=3.6$ ${\mathrm{\AA{}}}^{2}$, ${Q}_{21}(^{2}P_{\frac{1}{2}}\ensuremath{\leftarrow}^{2}P_{\frac{3}{2}})=16.2$ ${\mathrm{\AA{}}}^{2}$, ${Q}_{10}(^{2}S_{\frac{1}{2}}\ensuremath{\leftarrow}^{2}P_{\frac{1}{2}})=55.2$ ${\mathrm{\AA{}}}^{2}$, ${Q}_{20}(^{2}S_{\frac{1}{2}}\ensuremath{\leftarrow}^{2}P_{\frac{3}{2}})=63.5$ ${\mathrm{\AA{}}}^{2}$. For Cs-${\mathrm{H}}_{2}$ collisions: ${Q}_{12}=6.7$ ${\mathrm{\AA{}}}^{2}$, ${Q}_{21}=29.6$ ${\mathrm{\AA{}}}^{2}$, ${Q}_{10}=11.7$ ${\mathrm{\AA{}}}^{2}$, ${Q}_{20}=6.7$ ${\mathrm{\AA{}}}^{2}$. The large sizes of the excitation-transfer cross sections, which are comparable to the corresponding Cs-Cs cross sections, are attributed to resonances with transitions in the molecules.

Physical Review•Jan 5, 1967•41 citations

SENSITIZED FLUORESCENCE IN VAPORS OF ALKALI METALS: V. ENERGY TRANSFER IN COLLISIONS BETWEEN CESIUM AND INERT GAS ATOMS

M. Czajkowski, D. A. McGillis, L. Krause

The total cross sections for excitation transfer between the 6 2P1/2 and 6 2P3/2 levels in cesium, induced by collisions of the second kind between cesium and inert gas atoms, have been determined using methods of sensitized fluorescence. The experiments were carried out at a cesium vapor pressure of 1 × 10−6 mm Hg, at which there is no trapping of resonance radiation, and over a range of inert gas pressures extending from 1 to 300 mm Hg. The cross sections Q1(2P1/2 → P3/2) and Q2(2P1/2 ← 2P3/2) are as follows: Cs–He: 5.7 × 10−21 and 3.9 × 10−20 cm2; Cs–Ne: 1.9 × 10−21 and 3.1 × 10−20 cm2; Cs–A: 1.6 × 10−21 and 5.2 × 10−20 cm2; Cs–Kr: 8.3 × 10−21 and 18.4 × 10−20 cm2; Cs–Xe: 7.2 × 10−21 and 27.4 × 10−20 cm2. A mechanism for the excitation transfer is suggested, which involves an interaction between the inert gas atoms and the 6 2P electron in cesium, behaving as a free particle.

Canadian Journal of Physics•Jan 1, 1966•31 citations

SENSITIZED FLUORESCENCE IN VAPORS OF ALKALI METALS: VI. ENERGY TRANSFER IN COLLISIONS BETWEEN RUBIDIUM AND INERT GAS ATOMS

Bruce Pitre, A. G. A. Rae, L. Krause

The total cross sections for inelastic collisions between rubidium and inert gas atoms, leading to a transfer of excitation between the 5 2P1/2 and 5 2P3/2 levels in rubidium, have been determined in a study of sensitized fluorescence in rubidium – inert gas mixtures. The experiments were performed at a rubidium vapor pressure of 1.5 × 10−6 mm Hg, at which there is no imprisonment of resonance radiation, and over a range of inert gas pressures extending from 1 to 350 mm Hg. The cross sections Q1(5 2P1/2 → 5 2P3/2) and Q2(5 2P1/2 ← 5 2P3/2) are as follows: Rb–He: 7.6 × 10−18 and 10.3 × 10−18 cm2; Rb–Ne: 1.7 × 10−19 and 2.3 × 10−19 cm2; Rb–A: 1.0 × 10−19 and 1.6 × 10−19 cm2; Rb–Kr: 6.4 × 10−20 and 1.5 × 10−19 cm2; Rb–Xe: 7.9 × 10−20 and 2.1 × 10−19 cm2. The cross sections are subject to two apparent anomalies: they do not vary monotonically with the polarizabilities of the inert gases and not all of their ratios Q1/Q2 have values predicted by the principle of detailed balancing. These properties of the cross sections, as well as a partial disagreement with Franck's rule, are interpreted qualitatively in terms of a "free particle" interaction between the inert gas atoms and the 5 2P orbital electron in rubidium. A competing process involving three-body collisions and the possible formation of Rb – inert gas van der Waals' molecules is also suggested.

Canadian Journal of Physics•Apr 1, 1966•38 citations

Sensitized Fluorescence in Vapors of Alkali Atoms. XIII. 62P1/2−62P3/2 Excitation Transfer in Rubidium, Induced in Collisions with Noble Gas Atoms

I. N. Siara, E. S. Hrycyshyn, L. Krause

The cross sections for excitation transfer between the 62P fine-structure substates in rubidium, induced in collisions with noble gas atoms, have been determined in a series of sensitized fluorescence experiments. Mixtures of rubidium vapor and noble gases at pressures varying in the range 0–5 Torr were irradiated with each component of the second 2P rubidium doublet in turn and the following cross sections for 2P mixing were obtained from measurements of sensitised-to-resonance fluorescent intensity ratios. Rb–He: Q12(2P1/2 → 2P3/2) = 29.3 Å2; Q21(2P1/2 ← 2P3/2) = 19.0 Å2. Rb–Ne: Q12 = 10.3 Å2; Q21 = 6.4 Å2. Rb–Ar: Q12 = 24.0 Å2; Q21 = 14.9 Å2. Rb–Kr: Q12 = 23.2 Å2; Q21 = 14.6 Å2. Rb–Xe: Q12 = 43.9 Å2; Q21 = 27.7 Å2 In their dependence on the magnitude of the fine-structure splitting, the values are consistent with previously determined cross sections for mixing in the first and third 2P doublets of alkali atoms.

Canadian Journal of Physics•Aug 15, 1972•19 citations

Sensitized fluorescence in vapors of alkali metals. XI Energy transfer in potassium–rubidium collisions

E. S. Hrycyshyn, L. Krause

Sensitized fluorescence in rubidium vapor, induced by collisions with excited potassium atoms, was investigated to determine the total cross sections for inelastic collisions between excited potassium atoms and rubidium atoms in their ground states. The collision cross sections for the various excitation transfer processes are as follows: Q12′ (K42P1/2 → Rb52P3/2) = 40 Å2, Q22′ (K42P3/2 → Rb52P3/2) = 27 Å2, Q11′ (K42P1/2 → Rb52P1/2) = 2.7 Å2, and Q21′ (K42P3/2 → Rb52P1/2) = 1.9 Å2. The partial pressure of potassium vapor in the K–Rb mixture was kept largely below 10−5 mm Hg to eliminate effects due to the trapping of potassium resonance radiation.

Canadian Journal of Physics•Jan 15, 1969•15 citations

Inelastic collisions between excited alkali atoms and molecules. V. Sensitized fluorescence in mixtures of sodium with N2, H2, HD, and D2

M. Stupavsky, L. Krause

3 2P1/2 ↔ 3 2P3/2 excitation transfer in sodium, induced in inelastic collisions with ground-state N2, H2, HD, and D2 molecules, has been investigated in a series of sensitized fluorescence experiments. Mixtures of sodium vapor at a pressure of 5 × 10−7 Torr, and the gases, were irradiated with each NaD component in turn, and the fluorescence which contained both D components was monitored at right angles to the direction of the exciting beam. Measurements of the relative intensities of the NaD fluorescent components yielded the following collision cross sections for excitation transfer. For Na–N2 collisions: Q12(2P1/2 → P3/2) = 144 Å2, Q21(2P1,2 ← 2P3/2) = 76 Å2 for Na–H2 collisions: Q12 = 80 Å2, Q21 = 42 Å2. For Na–HD collisions: Q12 = 84 Å2, Q21 = 44 Å2. For Na–D2 collisions: Q12 = 98 Å2, Q21 = 52 Å2. The cross sections Q21 exhibit a slight resonance effect between the atomic and molecular rotational transitions.

Canadian Journal of Physics•Oct 1, 1968•23 citations
An account of recent work is given by the author and co-workers on the experimental determination of cross sections for excitation transfer between the (2)P((1/2)) and (2)P(3/2)resonance levels in potassium, rubidium and cesium, induced by inelastic collisions with alkali atoms and inert gas atoms in their ground states. Forty values of cross sections were obtained in a series of sensitized fluorescence experiments, in which alkali vapors and vapor-gas mixtures were irradiated with one component of the appropriate alkali resonance doublet, and the relative intensities of both components appearing in the fluorescent light were measured. The experiments indicate that the collisional interaction between an alkali atom in a (2)P state and a ground state inert gas atom probably occurs between the inert gas atom and the (2)P alkali valence electron which behaves like a quasi-free particle.
Excitation transfer between the 62P126 ^{2}P_{\frac{1}{2}}62P21​​ and 62P326 ^{2}P_{\frac{3}{2}}62P23​​ resonance states in cesium, induced by Cs-N2{\mathrm{N}}_{2}N2​ and Cs-H2{\mathrm{H}}_{2}H2​ collisions, was observed in the first experiment of its kind, in which techniques of sensitized fluorescence are used to investigate collisional mixing between resonance states of alkali atoms in mixtures with molecular gases. The cesium-vapor-gas system, in which the cesium vapor pressure was low enough to avoid radiation trapping, was irradiated with a single component of the resonance doublet. The fluorescent light, which contained both components of the doublet, was monitored at right angles to the direction of excitation. Measurements of relative intensities of the fluorescent components yielded the following cross sections for excitation transfer and for quenching of resonance radiation. For Cs-N2{\mathrm{N}}_{2}N2​ collisions: ${Q}_{12}(^{2}P_{\frac{1}{2}}\ensuremath{\rightarrow}^{2}P_{\frac{3}{2}})=3.6$ A˚2{\mathrm{\AA{}}}^{2}A˚2, ${Q}_{21}(^{2}P_{\frac{1}{2}}\ensuremath{\leftarrow}^{2}P_{\frac{3}{2}})=16.2$ A˚2{\mathrm{\AA{}}}^{2}A˚2, ${Q}_{10}(^{2}S_{\frac{1}{2}}\ensuremath{\leftarrow}^{2}P_{\frac{1}{2}})=55.2$ A˚2{\mathrm{\AA{}}}^{2}A˚2, ${Q}_{20}(^{2}S_{\frac{1}{2}}\ensuremath{\leftarrow}^{2}P_{\frac{3}{2}})=63.5$ A˚2{\mathrm{\AA{}}}^{2}A˚2. For Cs-H2{\mathrm{H}}_{2}H2​ collisions: Q12=6.7{Q}_{12}=6.7Q12​=6.7 A˚2{\mathrm{\AA{}}}^{2}A˚2, Q21=29.6{Q}_{21}=29.6Q21​=29.6 A˚2{\mathrm{\AA{}}}^{2}A˚2, Q10=11.7{Q}_{10}=11.7Q10​=11.7 A˚2{\mathrm{\AA{}}}^{2}A˚2, Q20=6.7{Q}_{20}=6.7Q20​=6.7 A˚2{\mathrm{\AA{}}}^{2}A˚2. The large sizes of the excitation-transfer cross sections, which are comparable to the corresponding Cs-Cs cross sections, are attributed to resonances with transitions in the molecules.
The total cross sections for excitation transfer between the 6 2P1/2 and 6 2P3/2 levels in cesium, induced by collisions of the second kind between cesium and inert gas atoms, have been determined using methods of sensitized fluorescence. The experiments were carried out at a cesium vapor pressure of 1 × 10−6 mm Hg, at which there is no trapping of resonance radiation, and over a range of inert gas pressures extending from 1 to 300 mm Hg. The cross sections Q1(2P1/2 → P3/2) and Q2(2P1/2 ← 2P3/2) are as follows: Cs–He: 5.7 × 10−21 and 3.9 × 10−20 cm2; Cs–Ne: 1.9 × 10−21 and 3.1 × 10−20 cm2; Cs–A: 1.6 × 10−21 and 5.2 × 10−20 cm2; Cs–Kr: 8.3 × 10−21 and 18.4 × 10−20 cm2; Cs–Xe: 7.2 × 10−21 and 27.4 × 10−20 cm2. A mechanism for the excitation transfer is suggested, which involves an interaction between the inert gas atoms and the 6 2P electron in cesium, behaving as a free particle.
The total cross sections for inelastic collisions between rubidium and inert gas atoms, leading to a transfer of excitation between the 5 2P1/2 and 5 2P3/2 levels in rubidium, have been determined in a study of sensitized fluorescence in rubidium – inert gas mixtures. The experiments were performed at a rubidium vapor pressure of 1.5 × 10−6 mm Hg, at which there is no imprisonment of resonance radiation, and over a range of inert gas pressures extending from 1 to 350 mm Hg. The cross sections Q1(5 2P1/2 → 5 2P3/2) and Q2(5 2P1/2 ← 5 2P3/2) are as follows: Rb–He: 7.6 × 10−18 and 10.3 × 10−18 cm2; Rb–Ne: 1.7 × 10−19 and 2.3 × 10−19 cm2; Rb–A: 1.0 × 10−19 and 1.6 × 10−19 cm2; Rb–Kr: 6.4 × 10−20 and 1.5 × 10−19 cm2; Rb–Xe: 7.9 × 10−20 and 2.1 × 10−19 cm2. The cross sections are subject to two apparent anomalies: they do not vary monotonically with the polarizabilities of the inert gases and not all of their ratios Q1/Q2 have values predicted by the principle of detailed balancing. These properties of the cross sections, as well as a partial disagreement with Franck's rule, are interpreted qualitatively in terms of a "free particle" interaction between the inert gas atoms and the 5 2P orbital electron in rubidium. A competing process involving three-body collisions and the possible formation of Rb – inert gas van der Waals' molecules is also suggested.
The cross sections for excitation transfer between the 62P fine-structure substates in rubidium, induced in collisions with noble gas atoms, have been determined in a series of sensitized fluorescence experiments. Mixtures of rubidium vapor and noble gases at pressures varying in the range 0–5 Torr were irradiated with each component of the second 2P rubidium doublet in turn and the following cross sections for 2P mixing were obtained from measurements of sensitised-to-resonance fluorescent intensity ratios. Rb–He: Q12(2P1/2 → 2P3/2) = 29.3 Å2; Q21(2P1/2 ← 2P3/2) = 19.0 Å2. Rb–Ne: Q12 = 10.3 Å2; Q21 = 6.4 Å2. Rb–Ar: Q12 = 24.0 Å2; Q21 = 14.9 Å2. Rb–Kr: Q12 = 23.2 Å2; Q21 = 14.6 Å2. Rb–Xe: Q12 = 43.9 Å2; Q21 = 27.7 Å2 In their dependence on the magnitude of the fine-structure splitting, the values are consistent with previously determined cross sections for mixing in the first and third 2P doublets of alkali atoms.
Sensitized fluorescence in rubidium vapor, induced by collisions with excited potassium atoms, was investigated to determine the total cross sections for inelastic collisions between excited potassium atoms and rubidium atoms in their ground states. The collision cross sections for the various excitation transfer processes are as follows: Q12′ (K42P1/2 → Rb52P3/2) = 40 Å2, Q22′ (K42P3/2 → Rb52P3/2) = 27 Å2, Q11′ (K42P1/2 → Rb52P1/2) = 2.7 Å2, and Q21′ (K42P3/2 → Rb52P1/2) = 1.9 Å2. The partial pressure of potassium vapor in the K–Rb mixture was kept largely below 10−5 mm Hg to eliminate effects due to the trapping of potassium resonance radiation.
3 2P1/2 ↔ 3 2P3/2 excitation transfer in sodium, induced in inelastic collisions with ground-state N2, H2, HD, and D2 molecules, has been investigated in a series of sensitized fluorescence experiments. Mixtures of sodium vapor at a pressure of 5 × 10−7 Torr, and the gases, were irradiated with each NaD component in turn, and the fluorescence which contained both D components was monitored at right angles to the direction of the exciting beam. Measurements of the relative intensities of the NaD fluorescent components yielded the following collision cross sections for excitation transfer. For Na–N2 collisions: Q12(2P1/2 → P3/2) = 144 Å2, Q21(2P1,2 ← 2P3/2) = 76 Å2 for Na–H2 collisions: Q12 = 80 Å2, Q21 = 42 Å2. For Na–HD collisions: Q12 = 84 Å2, Q21 = 44 Å2. For Na–D2 collisions: Q12 = 98 Å2, Q21 = 52 Å2. The cross sections Q21 exhibit a slight resonance effect between the atomic and molecular rotational transitions.