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Physical Review Letters

Experimental Evidence of the Inversion of Angular Momentum During the Transfer of Excitation by Resonant Collisions in the 6P13 State of Mercury

B. Dodsworth, A. Omont

Published Feb 2, 1970• 9 citations
Publisher

Abstract

The zero-field level-crossing signal of even isotopes of natural Hg excited by resonant collisions from directly excited ${\mathrm{Hg}}^{198}$ atoms has been observed with circularly polarized light. The signal is proportional to the atomic "orientation" (mean value of the angular momentum of the excited atoms). The sense of this orientation is reversed when the excitation is transferred by collisions from ${\mathrm{Hg}}^{198}$ to other isotopes, as predicted by the theory.

DOI
10.1103/physrevlett.24.198

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6P13−6P03 Excitation Transfer in Mercury, Induced in Collisions with N2 Molecules

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The cross section for the transition $6^{3}P_{0}\ensuremath{\rightarrow}6^{3}P_{1}$ in mercury, induced in collisions with ${\mathrm{N}}_{2}$ molecules, has been determined by the method of delayed coincidences. The Hg $^{3}P_{1}$ state was excited by pulses of 2537-\AA{} Hg resonance radiation and the decay of the long-lived 2537-\AA{} afterglow was studied in relation to ${\mathrm{N}}_{2}$ pressure. The resulting cross section ${Q}_{12}(^{3}P_{0}\ensuremath{\rightarrow}^{3}P_{1})=4.18\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ ${\mathrm{\AA{}}}^{2}$ was found to be good agreement with the prediction of the principle of detailed balancing when compared with the cross section ${Q}_{21}(^{3}P_{1}\ensuremath{\rightarrow}^{3}P_{0})$. It was also found that, within the sensitivity of the method, collisions with ${\mathrm{N}}_{2}$ molecules do not quench $^{3}P_{1}$ or $^{3}P_{0}$ Hg atoms to the ground state.

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Polarization of S122 Ground State of Even Isotopes of Hg+ by Stepwise Electron Impact

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Physical Review Letters•Aug 4, 1969•6 citations

Isotope Effect in the Imprisonment of Resonance Radiation

Theodore D. Holstein, D. Alpert, A. O. McCoubrey

On theoretical grounds it is expected that the decay time of imprisoned resonance radiation in the vapor of a single even isotope of mercury should be some six times larger than that observed with the natural samples of mixed isotopic constitution. To investigate this effect experimentally, decay measurements were carried out with samples of ${\mathrm{Hg}}^{198}$ (3 percent ${\mathrm{Hg}}^{199}$ and 0.1 percent ${\mathrm{Hg}}^{200}$). For vapor densities $N\ensuremath{\lesssim}\frac{{10}^{14}}{\mathrm{cc}}$, the predicted effect was verified. For $N>\frac{{10}^{14}}{\mathrm{cc}}$, the observed decay time drops below that predicted theoretically for pure ${\mathrm{Hg}}^{198}$. This secondary effect is here attributed to the transfer of excitation from ${\mathrm{Hg}}^{198}$ to ${\mathrm{Hg}}^{199}$ and ${\mathrm{Hg}}^{200}$ by collisions of the second kind. Comparison of experimental data with an appropriately generalized theory permits estimation of the cross section for such collisions. The value so obtained is ${10}^{\ensuremath{-}13}$ ${\mathrm{cm}}^{2}$, some twenty times the gas-kinetic cross section, and in order-of-magnitude agreement with theoretical expectations.

Physical Review•Mar 15, 1952•55 citations
The zero-field level-crossing signal of even isotopes of natural Hg excited by resonant collisions from directly excited Hg198{\mathrm{Hg}}^{198}Hg198 atoms has been observed with circularly polarized light. The signal is proportional to the atomic "orientation" (mean value of the angular momentum of the excited atoms). The sense of this orientation is reversed when the excitation is transferred by collisions from Hg198{\mathrm{Hg}}^{198}Hg198 to other isotopes, as predicted by the theory.
A detailed calculation of the relaxation matrix of resonance atomic states by resonant collisions is carried out in the semiclassical impact theory. The validity of the different approximations is discussed. These results have been tested by observing self-broadening of level-crossing curves in high field and in zero field, in the 63P16^{3}P_{1}63P1​ state in mercury. Observation of these signals at high pressures is very difficult with a pure isotope because of strong absorption and trapping of resonance light in the vapor; it is made very easy by observing level-crossing signals of one isotope in a very low concentration in the vapor of another isotope. Collisions between the different pairs of mercury isotopes have been thus systematically studied. Results are in excellent agreement (10%) with theory, both for the absolute value of cross sections and for the ratio of orientation broadening to alignment broadening.
The authors report results of the experimental study of excitation transfer between Zeeman sublevels of the 63P16^{3}P_{1}63P1​ state of an even isotope of mercury in magnetic fields up to 80 kG, obtained by monitoring the transition from sudden to partially adiabatic collisions. The results are shown to be in good agreement with theoretical evaluations based on a numerical solution of the relaxation problem or on a correlation-function description using a ${R}^{\ensuremath{-}3}$ dipole-dipole interaction.
Excitation of atoms in a vapor by polarized light produces unequal population of the magnetic sublevels of the excited state. The emitted optical resonance radiation is therefore partly polarized. The application of radiofrequency or microwave fields at a magnetic resonance frequency will induce transitions between sublevels of the excited state. The degree of polarization of the emitted optical resonance radiation is altered when the magnetic resonance condition is fulfilled. As suggested by Brossel and Kastler, this effect may be used to reveal the structure of the energy level. A detailed theory applicable to, and experiments on the 3P1^{3}P_{1}3P1​ state of all the isotopes of mercury are reported. The results obtained indicate that double resonance phenomena constitute a valuable new tool for investigating the structure of atomic energy levels. The mean life of the 3P1^{3}P_{1}3P1​ state is shown by observations on the resonance line widths to be 1.55\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}7}$ sec for all the isotopes. The ggg-factor of the 3P1^{3}P_{1}3P1​ state for isotopes with zero spin, measured in terms of the proton ggg-factor, is 1.4838\ifmmode\pm\else\textpm\fi{}0.0004.
The cross section for the transition $6^{3}P_{0}\ensuremath{\rightarrow}6^{3}P_{1}$ in mercury, induced in collisions with N2{\mathrm{N}}_{2}N2​ molecules, has been determined by the method of delayed coincidences. The Hg 3P1^{3}P_{1}3P1​ state was excited by pulses of 2537-\AA{} Hg resonance radiation and the decay of the long-lived 2537-\AA{} afterglow was studied in relation to N2{\mathrm{N}}_{2}N2​ pressure. The resulting cross section ${Q}_{12}(^{3}P_{0}\ensuremath{\rightarrow}^{3}P_{1})=4.18\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ A˚2{\mathrm{\AA{}}}^{2}A˚2 was found to be good agreement with the prediction of the principle of detailed balancing when compared with the cross section ${Q}_{21}(^{3}P_{1}\ensuremath{\rightarrow}^{3}P_{0})$. It was also found that, within the sensitivity of the method, collisions with N2{\mathrm{N}}_{2}N2​ molecules do not quench 3P1^{3}P_{1}3P1​ or 3P0^{3}P_{0}3P0​ Hg atoms to the ground state.
The 6s2S126s^{2}S_{\frac{1}{2}}6s2S21​​ ground ionic state of even isotopes of mercury was polarized in a stepwise excitation process from the atomic $6{s}^{2}^{1}S_{0}$ ground state via the metastable 6s6p3P26s6p^{3}P_{2}6s6p3P2​ state. The latter was optically pumped with polarized 5461-\AA{} ($6s7s^{3}S_{1}\ensuremath{-}^{3}P_{2}$) radiation. Paramagnetic resonance, observed by monitoring the change in intensity of the relatively intense 2851-\AA{} ($5{d}^{9}6{s}^{2}^{2}D_{\frac{5}{2}}\ensuremath{-}5{d}^{10}6s^{2}S_{\frac{1}{2}}$) electric quadrupole resonance radiation, was used to determine the polarization of the even-isotope ground-state ion to be 15%. If one assumes conservation of spin angular momentum, this process should yield highly polarized electrons.
On theoretical grounds it is expected that the decay time of imprisoned resonance radiation in the vapor of a single even isotope of mercury should be some six times larger than that observed with the natural samples of mixed isotopic constitution. To investigate this effect experimentally, decay measurements were carried out with samples of Hg198{\mathrm{Hg}}^{198}Hg198 (3 percent Hg199{\mathrm{Hg}}^{199}Hg199 and 0.1 percent Hg200{\mathrm{Hg}}^{200}Hg200). For vapor densities $N\ensuremath{\lesssim}\frac{{10}^{14}}{\mathrm{cc}}$, the predicted effect was verified. For N>1014ccN>\frac{{10}^{14}}{\mathrm{cc}}N>cc1014​, the observed decay time drops below that predicted theoretically for pure Hg198{\mathrm{Hg}}^{198}Hg198. This secondary effect is here attributed to the transfer of excitation from Hg198{\mathrm{Hg}}^{198}Hg198 to Hg199{\mathrm{Hg}}^{199}Hg199 and Hg200{\mathrm{Hg}}^{200}Hg200 by collisions of the second kind. Comparison of experimental data with an appropriately generalized theory permits estimation of the cross section for such collisions. The value so obtained is ${10}^{\ensuremath{-}13}$ cm2{\mathrm{cm}}^{2}cm2, some twenty times the gas-kinetic cross section, and in order-of-magnitude agreement with theoretical expectations.