Physical Review A

Three lowest bound states of Mg−

Donald R. Beck

Published Dec 1, 1984• 27 citations

Abstract

We calculate, including many-body effects, that the three lowest bound states of ${\mathrm{Mg}}^{\ensuremath{-}}$, $2{p}^{6}3s3{p}^{2}^{4}P$, $2{p}^{6}3{p}^{3}^{4}S^{0}$ and $2{p}^{5}3s3{p}^{3}^{6}P$, have electron affinities 0.360, 0.514, and 1.321 eV, respectively. The transition $3s3{p}^{2}^{4}P\ensuremath{\rightarrow}3{p}^{3}^{4}S^{0}$ is found to have an electric dipole oscillator strength of 0.295. The lifetimes of the $J=\frac{1}{2}, \frac{3}{2}, \mathrm{and} \frac{5}{2}$, $^{4}P$ levels are estimated to be 7.8, 9.8, and 1.6 ns, respectively.

DOI: 10.1103/physreva.30.3305

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Wavelength, oscillator strength, and fine structure for the →44 S° transition of Mg−

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Binding energy of the lowest state of negative beryllium

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Experimental Determination of the Mg24 I (3s3p)P23 Lifetime

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Physical Review A

Three lowest bound states of Mg−

Donald R. Beck

Published Dec 1, 1984• 27 citations

Publisher

Abstract

We calculate, including many-body effects, that the three lowest bound states of

{\mathrm{Mg}}^{\ensuremath{-}}

2{p}^{6}3s3{p}^{2}^{4}P

2{p}^{6}3{p}^{3}^{4}S^{0}

and

2{p}^{5}3s3{p}^{3}^{6}P

, have electron affinities 0.360, 0.514, and 1.321 eV, respectively. The transition

3s3{p}^{2}^{4}P\ensuremath{\rightarrow}3{p}^{3}^{4}S^{0}

is found to have an electric dipole oscillator strength of 0.295. The lifetimes of the

J=\frac{1}{2}, \frac{3}{2}, \mathrm{and} \frac{5}{2}

^{4}P

levels are estimated to be 7.8, 9.8, and 1.6 ns, respectively.

DOI: 10.1103/physreva.30.3305

Related papers

Wavelength, oscillator strength, and fine structure for the →44 S° transition of Mg−

Donald R. Beck

We have calculated the electron affinities, including many-body and relativistic effects, of ${\mathrm{Mg}}^{\mathrm{\ensuremath{-}}}$ $^{4}\mathrm{P}$ and ${\mathrm{Mg}}^{\mathrm{\ensuremath{-}}}$ $^{4}\mathrm{\ifmmode^\circ\else\textdegree\fi{}}$ to be 321 and 536 meV, respectively. The electric dipole f value for the $^{4}\ensuremath{\rightarrow}^{4}$S\ifmmode^\circ\else\textdegree\fi{} transition is 0.3087 (length) and 0.3000 (velocity), occurring at a theoretically predicted wavelength of 2921 A\r{}. The J=1/2\ensuremath{\rightarrow}3/2 fine-structure splitting for ${\mathrm{Mg}}^{\mathrm{\ensuremath{-}}}$ $^{4}\mathrm{P}$ is predicted to be 11.8 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$, and the J=3/2\ensuremath{\rightarrow}5/2 splitting 19.4 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$. These results should help in the attempt being made by Andersen (private communiation) to observe the $^{4}\ensuremath{\rightarrow}^{4}$S\ifmmode^\circ\else\textdegree\fi{} transition in the laboratory.We have calculated the electron affinities, including many-body and relativistic effects, of ${\mathrm{Mg}}^{\mathrm{\ensuremath{-}}}$ $^{4}\mathrm{P}$ and ${\mathrm{Mg}}^{\mathrm{\ensuremath{-}}}$ $^{4}\mathrm{\ifmmode^\circ\else\textdegree\fi{}}$ to be 321 and 536 meV, respectively. The electric dipole f value for the $^{4}\ensuremath{\rightarrow}^{4}$S\ifmmode^\circ\else\textdegree\fi{} transition is 0.3087 (length) and 0.3000 (velocity), occurring at a theoretically predicted wavelength of 2921 A\r{}. The J=1/2\ensuremath{\rightarrow}3/2 fine-structure splitting for ${\mathrm{Mg}}^{\mathrm{\ensuremath{-}}}$ $^{4}\mathrm{P}$ is predicted to be 11.8 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$, and the J=3/2\ensuremath{\rightarrow}5/2 splitting 19.4 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$. These results should help in the attempt being made by Andersen (private communiation) to observe the $^{4}\ensuremath{\rightarrow}^{4}$S\ifmmode^\circ\else\textdegree\fi{} transition in the laboratory.

Physical Review ASep 1, 198915 citations

Binding energy of the lowest state of negative beryllium

Annik Vivier Bunge

Accurate eigenvalues of Schr\"odinger's nonrelativistic equation for Be (1${s}^{2} $2s2p$ {)}^{3}$P and ${\mathrm{Be}}^{\mathrm{\ensuremath{-}}}$ (1${s}^{2} $2s2$ {p}^{2}$ ${)}^{4}$ P have been calculated yielding a corresponding electron affinity A of 276.1\ifmmode\pm\else\textpm\fi{}6.5 meV. The absolute term value of ${\mathrm{Be}}^{\mathrm{\ensuremath{-}}}$ (relative to the Be ground state) obtained as the difference between the experimental term value of Be $^{3}\mathrm{P}$ and A is 2.4492\ifmmode\pm\else\textpm\fi{}0.0065 eV, in agreement with a recent measurement of 2.53\ifmmode\pm\else\textpm\fi{}0.11 eV.Accurate eigenvalues of Schr\"odinger's nonrelativistic equation for Be (1${s}^{2}$2s2p${)}^{3}$P and ${\mathrm{Be}}^{\mathrm{\ensuremath{-}}}$ (1${s}^{2}$2s2${p}^{2}$${)}^{4}$P have been calculated yielding a corresponding electron affinity A of 276.1\ifmmode\pm\else\textpm\fi{}6.5 meV. The absolute term value of ${\mathrm{Be}}^{\mathrm{\ensuremath{-}}}$ (relative to the Be ground state) obtained as the difference between the experimental term value of Be $^{3}\mathrm{P}$ and A is 2.4492\ifmmode\pm\else\textpm\fi{}0.0065 eV, in agreement with a recent measurement of 2.53\ifmmode\pm\else\textpm\fi{}0.11 eV.

Physical Review AJan 1, 198629 citations

Transition properties of a potassium atom

D. K. Nandy, Yashpal Singh, Balkrishna P. Shah +1 more

We report here oscillator strengths, transition rates, branching ratios, and lifetimes due to the allowed transitions in the potassium (K) atom. We evaluate electric dipole ( $E1$ ) amplitudes using an all-order relativistic many-body perturbation method. The obtained results are compared with previously available experimental and theoretical studies. Using the $E1$ matrix elements mentioned above and estimated from the lifetimes of the $4p{\phantom{\rule{4pt}{0ex}}}^{2}\phantom{\rule{-0.16em}{0ex}}{P}_{1/2,3/2}$ states, we determine precise values of static and dynamic polarizabilities for the first five low-lying states in the considered atom. The static polarizabilities of the ground and $4p{\phantom{\rule{4pt}{0ex}}}^{2}\phantom{\rule{-0.16em}{0ex}}{P}_{1/2,3/2}$ states in the present work are more precise than the available measurements in these states. Only the present work employs relativistic theory to evaluate the polarizabilities in the $3d{\phantom{\rule{4pt}{0ex}}}^{2}\phantom{\rule{-0.16em}{0ex}}{D}_{3/2,5/2}$ states for which no experimental results are known with which to compare. We also reexamine ``magic wavelengths'' for the $4p{\phantom{\rule{4pt}{0ex}}}^{2}\phantom{\rule{-0.16em}{0ex}}{P}_{1/2}\ensuremath{\rightarrow}4s{\phantom{\rule{4pt}{0ex}}}^{2}\phantom{\rule{-0.16em}{0ex}}{S}_{1/2}$ and $4p{\phantom{\rule{4pt}{0ex}}}^{2}\phantom{\rule{-0.16em}{0ex}}{P}_{3/2}\ensuremath{\rightarrow}4s{\phantom{\rule{4pt}{0ex}}}^{2}\phantom{\rule{-0.16em}{0ex}}{S}_{1/2}$ transitions due to the linearly polarized light, which are useful to perform the state-insensitive trapping of K atoms.We report here oscillator strengths, transition rates, branching ratios, and lifetimes due to the allowed transitions in the potassium (K) atom. We evaluate electric dipole ($E1$) amplitudes using an all-order relativistic many-body perturbation method. The obtained results are compared with previously available experimental and theoretical studies. Using the $E1$ matrix elements mentioned above and estimated from the lifetimes of the $4p{\phantom{\rule{4pt}{0ex}}}^{2}\phantom{\rule{-0.16em}{0ex}}{P}_{1/2,3/2}$ states, we determine precise values of static and dynamic polarizabilities for the first five low-lying states in the considered atom. The static polarizabilities of the ground and $4p{\phantom{\rule{4pt}{0ex}}}^{2}\phantom{\rule{-0.16em}{0ex}}{P}_{1/2,3/2}$ states in the present work are more precise than the available measurements in these states. Only the present work employs relativistic theory to evaluate the polarizabilities in the $3d{\phantom{\rule{4pt}{0ex}}}^{2}\phantom{\rule{-0.16em}{0ex}}{D}_{3/2,5/2}$ states for which no experimental results are known with which to compare. We also reexamine ``magic wavelengths'' for the $4p{\phantom{\rule{4pt}{0ex}}}^{2}\phantom{\rule{-0.16em}{0ex}}{P}_{1/2}\ensuremath{\rightarrow}4s{\phantom{\rule{4pt}{0ex}}}^{2}\phantom{\rule{-0.16em}{0ex}}{S}_{1/2}$ and $4p{\phantom{\rule{4pt}{0ex}}}^{2}\phantom{\rule{-0.16em}{0ex}}{P}_{3/2}\ensuremath{\rightarrow}4s{\phantom{\rule{4pt}{0ex}}}^{2}\phantom{\rule{-0.16em}{0ex}}{S}_{1/2}$ transitions due to the linearly polarized light, which are useful to perform the state-insensitive trapping of K atoms.

arXiv:1209.5857Physical Review ANov 27, 201223 citations

Hyperfine quenching of the metastable P0,23 states in divalent atoms

S. G. Porsev, Andrei Derevianko

Hyperfine quenching rates of the lowest-energy metastable $^{3}P_{0}$ and $^{3}P_{2}$ states of Mg, Ca, Sr, and Yb atoms are computed. The calculations are carried out using ab initio relativistic many-body methods. The computed lifetimes may be useful for designing novel ultraprecise optical clocks and trapping experiments with the $^{3}P_{2}$ fermionic isotopes. The resulting natural widths of the $^{3}P_{0}\ensuremath{-}^{1}S_{0}$ clock transition are $0.44\phantom{\rule{0.3em}{0ex}}\text{mHz}$ for $^{25}\mathrm{Mg}$ , $2.2\phantom{\rule{0.3em}{0ex}}\text{mHz}$ for $^{43}\mathrm{Ca}$ , $7.6\phantom{\rule{0.3em}{0ex}}\text{mHz}$ for $^{87}\mathrm{Sr}$ , $43.5\phantom{\rule{0.3em}{0ex}}\text{mHz}$ for $^{171}\mathrm{Yb}$ , and $38.5\phantom{\rule{0.3em}{0ex}}\text{mHz}$ for $^{173}\mathrm{Yb}$ . Compared to the bosonic isotopes, the lifetime of the $^{3}P_{2}$ states in fermionic isotopes is noticeably shortened by the hyperfine quenching but still remains long enough for trapping experiments.Hyperfine quenching rates of the lowest-energy metastable $^{3}P_{0}$ and $^{3}P_{2}$ states of Mg, Ca, Sr, and Yb atoms are computed. The calculations are carried out using ab initio relativistic many-body methods. The computed lifetimes may be useful for designing novel ultraprecise optical clocks and trapping experiments with the $^{3}P_{2}$ fermionic isotopes. The resulting natural widths of the $^{3}P_{0}\ensuremath{-}^{1}S_{0}$ clock transition are $0.44\phantom{\rule{0.3em}{0ex}}\text{mHz}$ for $^{25}\mathrm{Mg}$, $2.2\phantom{\rule{0.3em}{0ex}}\text{mHz}$ for $^{43}\mathrm{Ca}$, $7.6\phantom{\rule{0.3em}{0ex}}\text{mHz}$ for $^{87}\mathrm{Sr}$, $43.5\phantom{\rule{0.3em}{0ex}}\text{mHz}$ for $^{171}\mathrm{Yb}$, and $38.5\phantom{\rule{0.3em}{0ex}}\text{mHz}$ for $^{173}\mathrm{Yb}$. Compared to the bosonic isotopes, the lifetime of the $^{3}P_{2}$ states in fermionic isotopes is noticeably shortened by the hyperfine quenching but still remains long enough for trapping experiments.

arXiv:physics/0312006Physical Review AApr 7, 2004117 citations

Experimental and theoretical study of bound and quasibound states of Ce−

C. W. Walter, N. D. Gibson, Y. G. Li +7 more

The negative ion of cerium is investigated experimentally with tunable infrared laser photodetachment spectroscopy and theoretically with relativistic configuration interaction in the continuum formalism. The relative cross section for neutral atom production is measured with a crossed ion-beam--laser-beam apparatus over the photon energy range of 0.54--0.75 eV. A rich resonance spectrum is revealed near the threshold with, at least, 12 peaks observed due to transitions from bound states of ${\mathrm{Ce}}^{\ensuremath{-}}$ to either bound or quasibound excited states of the negative ion. Theoretical calculations of the photodetachment cross sections enable identification of the transitions responsible for the measured peaks. Two of the peaks are due to electric dipole-allowed bound-bound transitions in ${\mathrm{Ce}}^{\ensuremath{-}}$, making cerium only the second atomic negative ion that has been demonstrated to support multiple bound states of opposite parity. In addition, combining the experimental data with the theoretical analysis determines the electron affinity of cerium to be 0.628(10) eV and the fine structure splitting of the ground state of ${\mathrm{Ce}}^{\ensuremath{-}}$ ( ${}^{4}\phantom{\rule{-0.16em}{0ex}}{H}_{7/2}--{}^{4}\phantom{\rule{-0.16em}{0ex}}{H}_{9/2}$ ) to be 0.097 75(4) eV.The negative ion of cerium is investigated experimentally with tunable infrared laser photodetachment spectroscopy and theoretically with relativistic configuration interaction in the continuum formalism. The relative cross section for neutral atom production is measured with a crossed ion-beam--laser-beam apparatus over the photon energy range of 0.54--0.75 eV. A rich resonance spectrum is revealed near the threshold with, at least, 12 peaks observed due to transitions from bound states of ${\mathrm{Ce}}^{\ensuremath{-}}$ to either bound or quasibound excited states of the negative ion. Theoretical calculations of the photodetachment cross sections enable identification of the transitions responsible for the measured peaks. Two of the peaks are due to electric dipole-allowed bound-bound transitions in ${\mathrm{Ce}}^{\ensuremath{-}}$, making cerium only the second atomic negative ion that has been demonstrated to support multiple bound states of opposite parity. In addition, combining the experimental data with the theoretical analysis determines the electron affinity of cerium to be 0.628(10) eV and the fine structure splitting of the ground state of ${\mathrm{Ce}}^{\ensuremath{-}}$ (${}^{4}\phantom{\rule{-0.16em}{0ex}}{H}_{7/2}--{}^{4}\phantom{\rule{-0.16em}{0ex}}{H}_{9/2}$) to be 0.097 75(4) eV.

Physical Review ASep 21, 201151 citations

Experimental Determination of the Mg24 I (3s3p)P23 Lifetime

Brian B. Jensen, He Ming, Philip G. Westergaard +5 more

We present the first experimental determination of the electric-dipole forbidden $(3s3p)^{3}P_{2}\ensuremath{\rightarrow}(3{s}^{2})^{1}S_{0}$ ( $M2$ ) transition rate in $^{24}\mathrm{Mg}$ and compare to state-of-the-art theoretical predictions. Our measurement exploits a magnetic trap isolating the sample from perturbations and a magneto-optical trap as an amplifier converting each $^{3}P_{2}\ensuremath{\rightarrow}^{1}S_{0}$ decay event into millions of photons readily detected. The transition rate is determined to be $(4.87\ifmmode\pm\else\textpm\fi{}0.3)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}\text{ }\text{ }{\mathrm{s}}^{\ensuremath{-}1}$ corresponding to a $^{3}P_{2}$ lifetime of ${2050}_{\ensuremath{-}110}^{+140}$ sec. This value is in agreement with recent theoretical predictions, and to our knowledge the longest lifetime ever determined in a laboratory environment.We present the first experimental determination of the electric-dipole forbidden $(3s3p)^{3}P_{2}\ensuremath{\rightarrow}(3{s}^{2})^{1}S_{0}$ ($M2$) transition rate in $^{24}\mathrm{Mg}$ and compare to state-of-the-art theoretical predictions. Our measurement exploits a magnetic trap isolating the sample from perturbations and a magneto-optical trap as an amplifier converting each $^{3}P_{2}\ensuremath{\rightarrow}^{1}S_{0}$ decay event into millions of photons readily detected. The transition rate is determined to be $(4.87\ifmmode\pm\else\textpm\fi{}0.3)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}\text{ }\text{ }{\mathrm{s}}^{\ensuremath{-}1}$ corresponding to a $^{3}P_{2}$ lifetime of ${2050}_{\ensuremath{-}110}^{+140}$ sec. This value is in agreement with recent theoretical predictions, and to our knowledge the longest lifetime ever determined in a laboratory environment.

Physical Review LettersSep 7, 201114 citations

We calculate, including many-body effects, that the three lowest bound states of

{\mathrm{Mg}}^{\ensuremath{-}}

2{p}^{6}3s3{p}^{2}^{4}P

2{p}^{6}3{p}^{3}^{4}S^{0}

and

2{p}^{5}3s3{p}^{3}^{6}P

, have electron affinities 0.360, 0.514, and 1.321 eV, respectively. The transition

3s3{p}^{2}^{4}P\ensuremath{\rightarrow}3{p}^{3}^{4}S^{0}

is found to have an electric dipole oscillator strength of 0.295. The lifetimes of the

J=\frac{1}{2}, \frac{3}{2}, \mathrm{and} \frac{5}{2}

^{4}P

levels are estimated to be 7.8, 9.8, and 1.6 ns, respectively.

We have calculated the electron affinities, including many-body and relativistic effects, of ${\mathrm{Mg}}^{\mathrm{\ensuremath{-}}}$

^{4}\mathrm{P}

and ${\mathrm{Mg}}^{\mathrm{\ensuremath{-}}}$ $^{4}\mathrm{\ifmmode^\circ\else\textdegree\fi{}}$ to be 321 and 536 meV, respectively. The electric dipole f value for the $^{4}\ensuremath{\rightarrow}^{4}$S\ifmmode^\circ\else\textdegree\fi{} transition is 0.3087 (length) and 0.3000 (velocity), occurring at a theoretically predicted wavelength of 2921 A\r{}. The J=1/2\ensuremath{\rightarrow}3/2 fine-structure splitting for ${\mathrm{Mg}}^{\mathrm{\ensuremath{-}}}$

^{4}\mathrm{P}

is predicted to be 11.8 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$, and the J=3/2\ensuremath{\rightarrow}5/2 splitting 19.4 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$. These results should help in the attempt being made by Andersen (private communiation) to observe the $^{4}\ensuremath{\rightarrow}^{4}$S\ifmmode^\circ\else\textdegree\fi{} transition in the laboratory.

Accurate eigenvalues of Schr\"odinger's nonrelativistic equation for Be (1${s}^{2}

2s2p

{)}^{3}$P and ${\mathrm{Be}}^{\mathrm{\ensuremath{-}}}$ (1${s}^{2}

2s2

{p}^{2}$

{)}^{4}

P have been calculated yielding a corresponding electron affinity A of 276.1\ifmmode\pm\else\textpm\fi{}6.5 meV. The absolute term value of ${\mathrm{Be}}^{\mathrm{\ensuremath{-}}}$ (relative to the Be ground state) obtained as the difference between the experimental term value of Be

^{3}\mathrm{P}

and A is 2.4492\ifmmode\pm\else\textpm\fi{}0.0065 eV, in agreement with a recent measurement of 2.53\ifmmode\pm\else\textpm\fi{}0.11 eV.

We report here oscillator strengths, transition rates, branching ratios, and lifetimes due to the allowed transitions in the potassium (K) atom. We evaluate electric dipole (

E1

) amplitudes using an all-order relativistic many-body perturbation method. The obtained results are compared with previously available experimental and theoretical studies. Using the

E1

matrix elements mentioned above and estimated from the lifetimes of the

4p{\phantom{\rule{4pt}{0ex}}}^{2}\phantom{\rule{-0.16em}{0ex}}{P}_{1/2,3/2}

states, we determine precise values of static and dynamic polarizabilities for the first five low-lying states in the considered atom. The static polarizabilities of the ground and

4p{\phantom{\rule{4pt}{0ex}}}^{2}\phantom{\rule{-0.16em}{0ex}}{P}_{1/2,3/2}

states in the present work are more precise than the available measurements in these states. Only the present work employs relativistic theory to evaluate the polarizabilities in the

3d{\phantom{\rule{4pt}{0ex}}}^{2}\phantom{\rule{-0.16em}{0ex}}{D}_{3/2,5/2}

states for which no experimental results are known with which to compare. We also reexamine ``magic wavelengths'' for the $4p{\phantom{\rule{4pt}{0ex}}}^{2}\phantom{\rule{-0.16em}{0ex}}{P}_{1/2}\ensuremath{\rightarrow}4s{\phantom{\rule{4pt}{0ex}}}^{2}\phantom{\rule{-0.16em}{0ex}}{S}_{1/2}$ and $4p{\phantom{\rule{4pt}{0ex}}}^{2}\phantom{\rule{-0.16em}{0ex}}{P}_{3/2}\ensuremath{\rightarrow}4s{\phantom{\rule{4pt}{0ex}}}^{2}\phantom{\rule{-0.16em}{0ex}}{S}_{1/2}$ transitions due to the linearly polarized light, which are useful to perform the state-insensitive trapping of K atoms.

Hyperfine quenching rates of the lowest-energy metastable

^{3}P_{0}

and

^{3}P_{2}

states of Mg, Ca, Sr, and Yb atoms are computed. The calculations are carried out using ab initio relativistic many-body methods. The computed lifetimes may be useful for designing novel ultraprecise optical clocks and trapping experiments with the

^{3}P_{2}

fermionic isotopes. The resulting natural widths of the $^{3}P_{0}\ensuremath{-}^{1}S_{0}$ clock transition are

0.44\phantom{\rule{0.3em}{0ex}}\text{mHz}

for

^{25}\mathrm{Mg}

2.2\phantom{\rule{0.3em}{0ex}}\text{mHz}

for

^{43}\mathrm{Ca}

7.6\phantom{\rule{0.3em}{0ex}}\text{mHz}

for

^{87}\mathrm{Sr}

43.5\phantom{\rule{0.3em}{0ex}}\text{mHz}

for

^{171}\mathrm{Yb}

, and

38.5\phantom{\rule{0.3em}{0ex}}\text{mHz}

for

^{173}\mathrm{Yb}

. Compared to the bosonic isotopes, the lifetime of the

^{3}P_{2}

states in fermionic isotopes is noticeably shortened by the hyperfine quenching but still remains long enough for trapping experiments.

{}^{4}\phantom{\rule{-0.16em}{0ex}}{H}_{7/2}--{}^{4}\phantom{\rule{-0.16em}{0ex}}{H}_{9/2}

) to be 0.097 75(4) eV.

We present the first experimental determination of the electric-dipole forbidden $(3s3p)^{3}P_{2}\ensuremath{\rightarrow}(3{s}^{2})^{1}S_{0}$ (

M2

) transition rate in

^{24}\mathrm{Mg}

and compare to state-of-the-art theoretical predictions. Our measurement exploits a magnetic trap isolating the sample from perturbations and a magneto-optical trap as an amplifier converting each $^{3}P_{2}\ensuremath{\rightarrow}^{1}S_{0}$ decay event into millions of photons readily detected. The transition rate is determined to be $(4.87\ifmmode\pm\else\textpm\fi{}0.3)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}\text{ }\text{ }{\mathrm{s}}^{\ensuremath{-}1}$ corresponding to a

^{3}P_{2}

lifetime of ${2050}_{\ensuremath{-}110}^{+140}$ sec. This value is in agreement with recent theoretical predictions, and to our knowledge the longest lifetime ever determined in a laboratory environment.