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Physical Review A

Detection of Nitrogen Atoms in the 2s(2p)33sS526 Metastable Autoionizing State

Clifford E. Fairchild, Hari Prasad Garg, C. E. Johnson

Published Aug 1, 1973• 7 citations
Publisher

Abstract

Metastable nitrogen atoms, produced by electron-impact dissociation of ${\mathrm{N}}_{2}$, have been detected in time-of-flight apparatuses located at Oregon State University and at University of California at Berkeley. Two different types of metastable atoms are detected; one type resembles Rydberg hydrogen atoms, while the other does not. The measured natural lifetime for the non-Rydberg atoms is 100 \ifmmode\pm\else\textpm\fi{} 25 \ensuremath{\mu}sec. Additional information regarding the identity of both types of metastable atoms is obtained by observing their quenching in a static electric field. The field-dependent decay constant for the Rydberg atoms is essentially a step function, and these atoms are entirely quenched by a field of 1.5 kV/cm. Both results are consistent with theory if the Rydberg atoms are in levels with principal quantum number greater than 25. The field-dependent decay constant for the non-Rydberg atoms varies quadratically with the strength of the applied electric field. In a field of 4 kV/cm applied along a 6-cm length of flight path, the value of this decay constant is 0.3 \ifmmode\times\else\texttimes\fi{} ${10}^{6}$ ${\mathrm{sec}}^{\ensuremath{-}1}$. The quenching results, together with the lifetime measurement, are a strong indication that the non-Rydberg atoms detected in the time-of-flight spectra are nitrogen atoms in the $2s{(2p)}^{3}3s^{6}S_{\frac{5}{2}}$ metastable autoionizing state.

DOI
10.1103/physreva.8.796

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Detection of nitrogen atoms in the 2s(2p)$sup 3$3s $sup 6$S/sub 5/2/ metastable autoionizing state

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Metastable nitrogen atoms, produced by electron-impact dissociation of N/ sub 2/, have been detected in time-of-flight apparatuses locatcd at Oregon State University and at University of California at Berkeley. Two different types of metastable atoms are detected; one type resembies Rydberg hydrogen atoms, while the other does not. The measured natural lifetime for the non-Rydberg atoms is 100 plus or minus 25 mu see. Additional infonnation regarding the identity of both types of metastable atoms is obtained by observing their quenching in a static electric field. The field-dependent decay constant for the Rydberg atoms is essentially a step function, and these atoms are entirely quenched by a field of 1.5 kV/cm. Both results are consistent with theory if the Rydberg atoms are in levels with principal quantum number greater than 25. The field-dependent decay constant for the non-Rydherg atoms varies quadratically with the strength of the applied electric field. In a field of 4 kV/cm applied along a 6-cm length of flight path, the value of this decay constant is 0.3 x 10/sup 6/ sec/sup -1/. The quenching results, together with the lifetime measurement, are a strong more » indication that the non-Rydberg atoms detected in the time-of-flight spectra are nitrogen atoms in the 2s(2p)/sup 3/3s /sup 6/S/sub 5/2/ metastable autoionizing state. (a uth) « less

Physical Review A•Aug 1, 1973•0 citations

Quenching of the 2S01 Metastable State of Helium by an Electric Field

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Auto-Ionizing States in the Alkali Atoms with Microsecond Lifetimes

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Measurement of Rydberg positronium fluorescence lifetimes

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Physical Review A•Jun 29, 2016•26 citations
Metastable nitrogen atoms, produced by electron-impact dissociation of N2{\mathrm{N}}_{2}N2​, have been detected in time-of-flight apparatuses located at Oregon State University and at University of California at Berkeley. Two different types of metastable atoms are detected; one type resembles Rydberg hydrogen atoms, while the other does not. The measured natural lifetime for the non-Rydberg atoms is 100 \ifmmode\pm\else\textpm\fi{} 25 \ensuremath{\mu}sec. Additional information regarding the identity of both types of metastable atoms is obtained by observing their quenching in a static electric field. The field-dependent decay constant for the Rydberg atoms is essentially a step function, and these atoms are entirely quenched by a field of 1.5 kV/cm. Both results are consistent with theory if the Rydberg atoms are in levels with principal quantum number greater than 25. The field-dependent decay constant for the non-Rydberg atoms varies quadratically with the strength of the applied electric field. In a field of 4 kV/cm applied along a 6-cm length of flight path, the value of this decay constant is 0.3 \ifmmode\times\else\texttimes\fi{} 106{10}^{6}106 sec\ensuremath−1{\mathrm{sec}}^{\ensuremath{-}1}sec\ensuremath−1. The quenching results, together with the lifetime measurement, are a strong indication that the non-Rydberg atoms detected in the time-of-flight spectra are nitrogen atoms in the 2s(2p)33s6S522s{(2p)}^{3}3s^{6}S_{\frac{5}{2}}2s(2p)33s6S25​​ metastable autoionizing state.
Detection of nitrogen atoms in the 2s(2p)$sup 3$3s sup6sup 6sup6S/sub 5/2/ metastable autoionizing state
Metastable nitrogen atoms, produced by electron-impact dissociation of N/ sub 2/, have been detected in time-of-flight apparatuses locatcd at Oregon State University and at University of California at Berkeley. Two different types of metastable atoms are detected; one type resembies Rydberg hydrogen atoms, while the other does not. The measured natural lifetime for the non-Rydberg atoms is 100 plus or minus 25 mu see. Additional infonnation regarding the identity of both types of metastable atoms is obtained by observing their quenching in a static electric field. The field-dependent decay constant for the Rydberg atoms is essentially a step function, and these atoms are entirely quenched by a field of 1.5 kV/cm. Both results are consistent with theory if the Rydberg atoms are in levels with principal quantum number greater than 25. The field-dependent decay constant for the non-Rydherg atoms varies quadratically with the strength of the applied electric field. In a field of 4 kV/cm applied along a 6-cm length of flight path, the value of this decay constant is 0.3 x 10/sup 6/ sec/sup -1/. The quenching results, together with the lifetime measurement, are a strong more » indication that the non-Rydberg atoms detected in the time-of-flight spectra are nitrogen atoms in the 2s(2p)/sup 3/3s /sup 6/S/sub 5/2/ metastable autoionizing state. (a uth) « less
A time-of-flight technique has been used to measure the quenching of the 21S02^{1}S_{0}21S0​ metastable state of helium by a static electric field. Neutral ground-state helium atoms effusing from a cooled source slit are immediately excited to the 21S02^{1}S_{0}21S0​ and 23S12^{3}S_{1}23S1​ metastable states by a pulse of antiparallel magnetically focused electrons. The metastable beam is collimated before passing through a uniform electric field region 0.5 m long and is then preferentially detected at the end of the time-of-flight region, 1.825 m from the electron gun. The time-of-flight distribution for the 21S02^{1}S_{0}21S0​ state is separated from that of the 23S12^{3}S_{1}23S1​ state by illuminating the beam before the electric field region with an rf-discharge helium lamp. The 21S02^{1}S_{0}21S0​ state is quenched by resonant absorption of a 20 581-\AA{} photon, raising the atom to the 21P12^{1}P_{1}21P1​ state, which then decays to the 1S0^{1}S_{0}1S0​ ground state; the 23S12^{3}S_{1}23S1​ state remains unaffected because it is the ground state for the triplet system. The 21S02^{1}S_{0}21S0​ time-of-flight distribution is therefore obtained from the difference between the full beam and the quenched beam. The number of 21S02^{1}S_{0}21S0​ atoms arriving at the detector in specific velocity intervals with the electric field off is compared to the number with the field on to determine the quenching rate (=kE2=k{E}^{2}=kE2). The result for the quenching constant kkk for both He3{\mathrm{He}}^{3}He3 and He4{\mathrm{He}}^{4}He4 with EEE in kV/cm is $k=0.933\ifmmode\pm\else\textpm\fi{}0.005$; this value is in good agreement with theory and with an earlier less accurate experiment. The error in the present experiment arises from a 0.5% uncertainty in the effective length of the electric field region.
Discrete atomic energy levels lying between the first and second ionization potentials which are metastable against both auto-ionization and radiative decay have been observed in the alkali elements. These levels arise from the excitation of an electron from the outermost closed shell of the atom and have characteristic lifetimes in the microsecond region. A beam of metastable alkali atoms is produced by electron bombardment of neutral ground-state atoms and is detected by collecting the charged products of the decay. Stern-Gerlach magnetic-deflection experiments have been performed to show unambiguously that the signals arise from paramagnetic atoms and not from possible stray-photon effects in the apparatus. The excitation energies, electron-bombardment production cross sections, natural lifetimes, and the tentative spectroscopic assignments of these atoms are listed below: The energy and lifetime of the metastable lithium atom are in good agreement with the available theoretical estimates. The metastable states in the heavier alkali atoms are classified in relation to the known Ib{\mathrm{I}}^{b}Ib spectral terms. Magnetic and electric fields have been found to be effective in reducing the lifetime of the metastable atoms. The Zeeman quenching is discussed in a separate paper. The Stark quenching rate has been found to be proportional to the square of the electric field and to increase rapidly with atomic number ZZZ. It is suggested that the Stark quenching results from a second-order interaction which involves the product of the electric field and the spin-orbit or other magnetic operators.
A time-of-flight technique has been used to measure the radiative lifetime of the 21S02 ^{1}S_{0}21S0​ state of helium. After passing from a cooled source, helium atoms are excited by a pulsed anti-parallel electron beam. The atomic beam then contains not only ground-state helium atoms but also metastable atoms in both the 23S12 ^{3}S_{1}23S1​ and the 21S02 ^{1}S_{0}21S0​ states. The metastable atoms are detected at two positions, 1.9 and 6.7 m from the electron gun, by Auger ejection of an electron from a copper target, the first of which is a 60% transmitting mesh. Ground-state helium atoms cannot cause an electron to be ejected and hence are not detected. The time-of-flight distribution for the metastable 21S02 ^{1}S_{0}21S0​ state is separated from that of the 23S12 ^{3}S_{1}23S1​ state by illuminating the beam with an rf-discharge helium lamp. The 21S02 ^{1}S_{0}21S0​ state is quenched by resonant absorption of a 20 581 - \AA{}A photon, raising the atom to the 21P12 ^{1}P_{1}21P1​ state, which then decays preferentially to the 1S0^{1}S_{0}1S0​ ground state; the 23S12 ^{3}S_{1}23S1​ state remains unaffected because it is the ground state for the triplet system. The time-of-flight distribution for the 21S02 ^{1}S_{0}21S0​ atoms is therefore obtained from the difference between the full beam and the quenched beam. A comparison of the number of 21S02 ^{1}S_{0}21S0​ metastables within a given velocity interval at the two detectors determines the number which decay in flight and yields a value for the two-photon radiative lifetime. The value of the singlet lifetime for both He3{\mathrm{He}}^{3}He3 and He4{\mathrm{He}}^{4}He4 is 19.7 \ifmmode\pm\else\textpm\fi{} 1.0 msec, agreeing with the theoretical value of 19.5 msec, but disagreeing with the value 38 \ifmmode\pm\else\textpm\fi{} 8 msec measured by Pearl using a movable detector. The 1.0-msec error is an estimate of the remaining systematic errors in the experiment.
We report measurements of the fluorescence lifetimes of positronium (Ps) atoms with principal quantum numbers n=10−−19n=10--19n=10−−19. Ps atoms in Rydberg-Stark states were produced via a two-color two-step $1\phantom{\rule{0.16em}{0ex}}^{3}S\ensuremath{\rightarrow}2\phantom{\rule{0.16em}{0ex}}^{3}P\ensuremath{\rightarrow}n\phantom{\rule{0.16em}{0ex}}^{3}S/n\phantom{\rule{0.16em}{0ex}}^{3}D$ excitation scheme and subsequently detected after traveling 1.2 m. The measured time-of-flight distributions were used to determine the mean lifetimes of the Rydberg levels, yielding values ranging from $3\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{s}$ to $26\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{s}$. Our data are in accord with the expected radiative lifetimes of Rydberg-Stark states of Ps.