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Physical Review

Radio-Frequency Resonance of the Metastable State (2P322 3S122)2 of Neon Produced and Aligned by Electron Impact

T. Hadeishi, Orilla A. McHarris, William A. Nierenberg

Published May 17, 1965• 9 citations
Publisher

Abstract

The metastable state ${(2^{2}P_{\frac{3}{2}} 3^{2}S_{\frac{1}{2}})}_{2}$ of neon was produced and aligned by electron impact. The diodestructure electron gun was operated at a high electron-current density under space-charge neutralization conditions. Radio-frequency resonance of the aligned metastable state ${(2^{2}P_{\frac{3}{2}} 3^{2}S_{\frac{1}{2}})}_{2}$ was observed by monitoring the change of absorption of the $\ensuremath{\lambda}6143$-resonance radiation passing through the gap between the cathode and anode. The neon metastable-state resonance was compared with the mercury metastable-state $6^{3}P_{2}$ radio-frequency resonance obtained by using the same gun for both, and observed by monitoring the absorption of the $\ensuremath{\lambda}5461$-resonance radiation passing through the same excitation region. The observed $\frac{{({g}_{J})}_{\mathrm{Ne}}}{{({g}_{J})}_{\mathrm{Hg}}}$ was 1.008\ifmmode\pm\else\textpm\fi{}0.024. This method could be applied to other atoms having a metastable state with $J>0$.

DOI
10.1103/physrev.138.a983

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The metastable state (22P3232S12)2{(2^{2}P_{\frac{3}{2}} 3^{2}S_{\frac{1}{2}})}_{2}(22P23​​32S21​​)2​ of neon was produced and aligned by electron impact. The diodestructure electron gun was operated at a high electron-current density under space-charge neutralization conditions. Radio-frequency resonance of the aligned metastable state (22P3232S12)2{(2^{2}P_{\frac{3}{2}} 3^{2}S_{\frac{1}{2}})}_{2}(22P23​​32S21​​)2​ was observed by monitoring the change of absorption of the \ensuremathλ6143\ensuremath{\lambda}6143\ensuremathλ6143-resonance radiation passing through the gap between the cathode and anode. The neon metastable-state resonance was compared with the mercury metastable-state 63P26^{3}P_{2}63P2​ radio-frequency resonance obtained by using the same gun for both, and observed by monitoring the absorption of the \ensuremathλ5461\ensuremath{\lambda}5461\ensuremathλ5461-resonance radiation passing through the same excitation region. The observed (gJ)Ne(gJ)Hg\frac{{({g}_{J})}_{\mathrm{Ne}}}{{({g}_{J})}_{\mathrm{Hg}}}(gJ​)Hg​(gJ​)Ne​​ was 1.008\ifmmode\pm\else\textpm\fi{}0.024. This method could be applied to other atoms having a metastable state with J>0J>0J>0.
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Metastable state produced in mercury vapor at low pressures by electron impacts of 4.9 volts.---The persistence of the "radiation" produced by 4.9 volt impacts in mercury vapor was measured in a four electrode tube of the type usually employed in resonance potential measurements, consisting of an equipotential cathode of simple design, an inner grid GGG for controlling the velocity of the impacting electrons, an outer photo-electric grid HHH and a photo-electric plate PPP. A.c. and d.c. voltages were applied to the two grids in such a way that the electrons had sufficient velocity to excite the radiation only in alternate half-cycles and that the photo-electric current to the electrometer alternated in direction simultaneously. As a result of the persistence of the radiation there resulted a decrease in the current with increasing frequency, reaching a minimum at 1800 cycles for a distance between grids of 17 mm and at 3800 cycles for a distance of 8.5 mm. These results did not vary much with pressure,.003 to.032 mm. They show a lapse of time between the excitation and the arrival of the first radiation at the plate PPP of about 1/3600 and 1/7600 sec. respectively. A mathematical discussion shows that the diffusion of the radiation by repeated emission and re-absorption (the "imprisonment" of radiation theory) cannot account for these results. A calculation, based on the assumption that the excited atoms remain in a metastable state and carry the energy of excitation to the photo-electric surfaces and there give it up, gives results in very close agreement with the observations. The conclusion is that a metastable state is formed by the atoms excited by the 4.9 volt electron impacts and that these are the effective ones in producing the photo-electric response in the tubes. In these experiments the 2p22{p}_{2}2p2​ state is the only one excited by the impacts in appreciable amount. How these results can be reconciled with the Bohr theory, according to which the 2p22{p}_{2}2p2​ state is not metastable, is not clear.
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The radiofreq'uency paragm.agnetic-re sonance m.ethod was used to observe the exchange collisions between th-e Xe ionic ground state 2P3/2 and the neutral metastable state 3 P2o The ionic ground-state and m.etastable-state atom.s are both form.edand aligned by unidirectional low-energy high-flux electron-beam.im.pact.The m.agnetic resonance of the ionic ground-state atom.s was observed by m.onitoring changes in the transparency of the resonance radiation absorbed by the m.etastable-state atom.s.The experim.ent is described in detail; along with a possible process for observing this resonance.Phenom.enologicaltheories are presented which m.ay explain the sign of the m.agnetic resonance signal of the ionic ground state com.pared with the m.etastable m.agnetic resonance.
A brief survey of the experiment on electronic excitation of atoms, carried on at the Atomic Beam Group of the Lawrence Radiation Laboratory, is made.By means of alignment of excited atoms by electron-impact excitation, we first observed rf paramagneticresonance reorientation of Hg and neon metastable states.Later on, the method was extended to observe the coherence property of excited atoms associated with the electron-impact excitation.The coherent excitation of nondegenerate levels of excited atoms results in intensity beats either in the fluorescent decay due to spontaneous radiation or in the resonance absorption by a long-lived metastable state.