arXiv:1504.03023 · Hyperfine Interactions

Lifetime measurement of the 5d2 D 5/2 state in Ba+

Amita Mohanty, Elwin Dijck, Mayerlin Nuñez Portela, Nivedya Valappol, Andrew T. Grier, T. B. Meijknecht, Lorenz Willmann, Klaus Peter Jungmann

Published Apr 20, 2015• 4 citations

arXiv HTML PDF

Abstract

The lifetime of the metastable 5d2 D 5/2 state has been measured for a single trapped Ba+ ion in a Paul trap in Ultra High Vacuum (UHV) in the 10−10 mbar pressure range. A total of 5046 individual periods when the ion was shelved in this state have been recorded. A preliminary value $\tau _{D_{5/2}} = 26.4(1.7)$ s is obtained through extrapolation to zero residual gas pressure.

DOI: 10.1007/s10751-015-1161-9

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Quantum jumps and the single trapped barium ion: Determination of collisional quenching rates for the 5 d2 D5/2 level

Alan A. Madej, J. D. Sankey

Physical Review AMar 1, 199075 citations

Lifetime measurement of the metastable 4dD5∕22 state in Sr+88 using a single trapped ion

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Radiative Lifetime Measurement of the Ba+ Metastable D3/2 State

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Radiative lifetimes of metastable states of Hg+ and Hg2+

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Physical Review ANov 1, 199020 citations

Measurement of the branching fractions and lifetime of the 5D5/2 level of Ba+

Carolyn Auchter, Thomas W. Noel, Matthew Hoffman +2 more

arXiv:1409.0873Physical Review ADec 17, 201426 citations

arXiv:1504.03023 · Hyperfine Interactions

Lifetime measurement of the 5d2 D 5/2 state in Ba+

Amita Mohanty, Elwin Dijck, Mayerlin Nuñez Portela, Nivedya Valappol, Andrew T. Grier, T. B. Meijknecht, Lorenz Willmann, Klaus Peter Jungmann

Published Apr 20, 2015• 4 citations

arXiv HTML PDF

Abstract

\tau _{D_{5/2}} = 26.4(1.7)

s is obtained through extrapolation to zero residual gas pressure.

DOI: 10.1007/s10751-015-1161-9

Related papers

Quantum jumps and the single trapped barium ion: Determination of collisional quenching rates for the 5 d2 D5/2 level

Alan A. Madej, J. D. Sankey

A single ${\mathrm{Ba}}^{+}$ atom was confined in a radio-frequency ion trap and cooled by near-resonant laser light. Quantum jumps into and out of the metastable 5d $^{2}D_{5/2}$ level were observed that followed the expected exponential distribution in dark periods to good agreement. Measurement of quantum-jump distributions together with careful measurements of the absolute partial pressures of all residual gas species enabled accurate measurements of the quenched 5d $^{2}D_{5/2}$ lifetime as a function of quenching gas pressure. Measurements of quenching were observed at pressures where the mean collision rate was on the order of 1 ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$. The results yielded quenching rate constants for the metastable level for a series of gases that typically make up the residual gas environment of ultra-high-vacuum systems ( ${\mathrm{H}}_{2}$ , He, ${\mathrm{CH}}_{4}$ , ${\mathrm{H}}_{2}$ O, CO, ${\mathrm{N}}_{2}$ , Ar, and ${\mathrm{CO}}_{2}$ ) together with an improved value of the ${5}^{2}$ ${\mathrm{D}}_{5/2}$ radiative lifetime of ${t}_{0}$ =34.5\ifmmode\pm\else\textpm\fi{}3.5 s. The above quenching rate constants were then compared with classical ion-molecule collision theory. It was found that the quenching rates for molecular gases were comparable to the classical collision rates, while the rates for atomic gases were considerably lower.A single ${\mathrm{Ba}}^{+}$ atom was confined in a radio-frequency ion trap and cooled by near-resonant laser light. Quantum jumps into and out of the metastable 5d $^{2}D_{5/2}$ level were observed that followed the expected exponential distribution in dark periods to good agreement. Measurement of quantum-jump distributions together with careful measurements of the absolute partial pressures of all residual gas species enabled accurate measurements of the quenched 5d $^{2}D_{5/2}$ lifetime as a function of quenching gas pressure. Measurements of quenching were observed at pressures where the mean collision rate was on the order of 1 ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$. The results yielded quenching rate constants for the metastable level for a series of gases that typically make up the residual gas environment of ultra-high-vacuum systems (${\mathrm{H}}_{2}$, He, ${\mathrm{CH}}_{4}$, ${\mathrm{H}}_{2}$O, CO, ${\mathrm{N}}_{2}$, Ar, and ${\mathrm{CO}}_{2}$) together with an improved value of the ${5}^{2}$${\mathrm{D}}_{5/2}$ radiative lifetime of ${t}_{0}$=34.5\ifmmode\pm\else\textpm\fi{}3.5 s. The above quenching rate constants were then compared with classical ion-molecule collision theory. It was found that the quenching rates for molecular gases were comparable to the classical collision rates, while the rates for atomic gases were considerably lower.

Physical Review AMar 1, 199075 citations

Lifetime measurement of the metastable 4dD5∕22 state in Sr+88 using a single trapped ion

V. Letchumanan, M. A. Wilson, Patrick Robert Gill +1 more

The natural lifetime of the metastable $4d\phantom{\rule{0.2em}{0ex}}^{2}D_{5∕2}$ state in $^{88}\mathrm{Sr}^{+}$ has been measured using a single laser-cooled, trapped ion. The ion was prepared in the $4d\phantom{\rule{0.2em}{0ex}}^{2}D_{5∕2}$ state by laser excitation of the $5s\phantom{\rule{0.2em}{0ex}}^{2}S_{1∕2}\ensuremath{-}4d\phantom{\rule{0.2em}{0ex}}^{2}D_{5∕2}$ quadrupole transition at 674 nm. The decay time was measured by using Dehmelt's electron shelving method to monitor the ion's electronic state. Two separate investigations were conducted under slightly different experimental conditions. 160 000 decay times from the $4d\phantom{\rule{0.2em}{0ex}}^{2}D_{5∕2}$ state were observed in total, and two different methods for determining the statistical value of the measured lifetime have been compared. Systematic effects have also been estimated, and including these effects yields a value of $\ensuremath{\tau}=390.8(1.6)\phantom{\rule{0.3em}{0ex}}\mathrm{ms}$ ($1\ensuremath{\sigma}$ uncertainty) for the natural lifetime.The natural lifetime of the metastable $4d\phantom{\rule{0.2em}{0ex}}^{2}D_{5∕2}$ state in $^{88}\mathrm{Sr}^{+}$ has been measured using a single laser-cooled, trapped ion. The ion was prepared in the $4d\phantom{\rule{0.2em}{0ex}}^{2}D_{5∕2}$ state by laser excitation of the $5s\phantom{\rule{0.2em}{0ex}}^{2}S_{1∕2}\ensuremath{-}4d\phantom{\rule{0.2em}{0ex}}^{2}D_{5∕2}$ quadrupole transition at 674 nm. The decay time was measured by using Dehmelt's electron shelving method to monitor the ion's electronic state. Two separate investigations were conducted under slightly different experimental conditions. 160 000 decay times from the $4d\phantom{\rule{0.2em}{0ex}}^{2}D_{5∕2}$ state were observed in total, and two different methods for determining the statistical value of the measured lifetime have been compared. Systematic effects have also been estimated, and including these effects yields a value of $\ensuremath{\tau}=390.8(1.6)\phantom{\rule{0.3em}{0ex}}\mathrm{ms}$ ($1\ensuremath{\sigma}$ uncertainty) for the natural lifetime.

Physical Review AJul 13, 200539 citations

Radiative Lifetime Measurement of the Ba+ Metastable D3/2 State

Nan Yu, Warren Nagourney, HANS G. DEHMELT

The extremely long lifetimes of the metastable $D$ states of the ${\mathrm{Ba}}^{+}$ ion make it difficult to measure them accurately due to their high sensitivity to collisional effects. Thus a discrepancy exists between theories and experiments for the ${\mathrm{Ba}}^{+}$ ${D}_{3/2}$ state. We have measured the ${D}_{3/2}$ lifetime under a nearly ideal condition, i.e., single trapped ${\mathrm{Ba}}^{+}$ ions in ultrahigh vacuum. The obtained value of $79.8\ifmmode\pm\else\textpm\fi{}4.6\mathrm{s}$ resolves the existing discrepancy. The collisional quenching is found insignificant in our experiment, but there are indications of a non-negligible fine-structure mixing effect.The extremely long lifetimes of the metastable $D$ states of the ${\mathrm{Ba}}^{+}$ ion make it difficult to measure them accurately due to their high sensitivity to collisional effects. Thus a discrepancy exists between theories and experiments for the ${\mathrm{Ba}}^{+}$ ${D}_{3/2}$ state. We have measured the ${D}_{3/2}$ lifetime under a nearly ideal condition, i.e., single trapped ${\mathrm{Ba}}^{+}$ ions in ultrahigh vacuum. The obtained value of $79.8\ifmmode\pm\else\textpm\fi{}4.6\mathrm{s}$ resolves the existing discrepancy. The collisional quenching is found insignificant in our experiment, but there are indications of a non-negligible fine-structure mixing effect.

Physical Review LettersJun 30, 199765 citations

Measurement of the lifetime of the 3d2D5/2 state in 40Ca+

P. A. Barton, C. J. S. Donald, D. M. Lucas +3 more

We report a measurement of the lifetime of the $3d{}^{2}{D}_{5/2}$ metastable level in ${}^{40}{\mathrm{Ca}}^{+},$ using quantum jumps of a single cold calcium ion in a linear Paul trap. The $4s{}^{2}{S}_{1/2}--3d{}^{2}{D}_{5/2}$ transition is significant for single-ion optical frequency standards, astrophysical references, and tests of atomic structure calculations. We obtain $\ensuremath{\tau}=1.168\ifmmode\pm\else\textpm\fi{}0.007$ s from observation of nearly $64000$ quantum jumps during $\ensuremath{\sim}32$ h. Our result is more precise and significantly larger than previous measurements. Experiments carried out to quantify systematic effects included a study of a previously unremarked source of systematic error, namely, excitation by the broad background of radiation emitted by a semiconductor diode laser. Combining our result with atomic structure calculations yields $1.20\ifmmode\pm\else\textpm\fi{}0.01$ s for the lifetime of $3d{}^{2}{D}_{3/2}.$ We also use quantum jump observations to demonstrate photon antibunching, and to estimate background pressure and heating rates in the ion trap.We report a measurement of the lifetime of the $3d{}^{2}{D}_{5/2}$ metastable level in ${}^{40}{\mathrm{Ca}}^{+},$ using quantum jumps of a single cold calcium ion in a linear Paul trap. The $4s{}^{2}{S}_{1/2}--3d{}^{2}{D}_{5/2}$ transition is significant for single-ion optical frequency standards, astrophysical references, and tests of atomic structure calculations. We obtain $\ensuremath{\tau}=1.168\ifmmode\pm\else\textpm\fi{}0.007$ s from observation of nearly $64000$ quantum jumps during $\ensuremath{\sim}32$ h. Our result is more precise and significantly larger than previous measurements. Experiments carried out to quantify systematic effects included a study of a previously unremarked source of systematic error, namely, excitation by the broad background of radiation emitted by a semiconductor diode laser. Combining our result with atomic structure calculations yields $1.20\ifmmode\pm\else\textpm\fi{}0.01$ s for the lifetime of $3d{}^{2}{D}_{3/2}.$ We also use quantum jump observations to demonstrate photon antibunching, and to estimate background pressure and heating rates in the ion trap.

arXiv:physics/0002026Physical Review AAug 14, 2000132 citations

Radiative lifetimes of metastable states of Hg+ and Hg2+

Anthony G. Calamai, Charles E. Johnson

The natural radiative lifetimes of the 5${\mathit{d}}^{9} $6$ {\mathit{s}}^{2}$ ${(}^{2}$ ${\mathit{D}}_{5/2}$ and $^{2}$ ${\mathit{D}}_{3/2}$ ) metastable states of ${\mathrm{Hg}}^{+}$ as well as of the 5${\mathit{d}}^{9} $6s$ {(}^{3}$${\mathit{D}}_{2}$) metastable state of ${\mathrm{Hg}}^{2+}$ have been measured by counting for equal time intervals either the 282-, 198-, or 217-nm photons emitted when the respective metastable ions decay to the ground state. The metastable Hg ions are produced inside a cylindrical electrostatic ion trap by electron bombardment of background Hg vapor maintained at pressures ranging from 4 to 50\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}8}$ Torr. The trap consists of a 5.0-cm-diam, 7.5-cm-long cylinder with end caps plus a concentric 0.003-cm-diam central cylinder maintained at a negative potential of 140 V. Following electron impact of the Hg vapor, some of the photons emitted by the decaying metastable ion population are focused onto a narrow-bandwidth interference filter. The photons transmitted by the filter are detected by a photomultiplier tube as a function of time and generate a decay curve. However, the signal detected with the interference filter used to monitor the $^{2}$${\mathit{D}}_{3/2}$ metastable-state population consists of two exponentially decaying components, indicating the presence of another metastable state decaying through the emission of a photon within the bandpass of the filter. The second component is assumed to arise from a cascade originating with the 5${\mathit{d}}^{9}$6s6p (J=9/2) metastable state of ${\mathrm{Hg}}^{+}$ . Therefore, as dictated by the composition of the photon decay curve, the pressure-dependent decay rates of the metastable states are obtained from a least-squares fit of either a single- or double-component exponential decay to the natural logarithm of the decay curve.Mean decay rates extrapolated to zero pressure of the background Hg vapor using a straight-line least-squares fit, and the inverse of the zero-pressure intercept yields the natural radiative lifetime of the relevant metastable state. Our results for the lifetimes of the $^{2}$ ${\mathit{D}}_{5/2}$ , $^{2}$ ${\mathit{D}}_{3/2}$ , and J=9/2 metastable states of ${\mathrm{Hg}}^{+}$ are 87\ifmmode\pm\else\textpm\fi{}4, 8.8\ifmmode\pm\else\textpm\fi{}0.4, and 60\ifmmode\pm\else\textpm\fi{}6 msec, respectively, while the lifetime of the ${\mathrm{Hg}}^{2+}$ ${(}^{3}$ ${\mathit{D}}_{2}$ ) metastable state is 34\ifmmode\pm\else\textpm\fi{}3 msec.The natural radiative lifetimes of the 5${\mathit{d}}^{9}$6${\mathit{s}}^{2}$ ${(}^{2}$${\mathit{D}}_{5/2}$ and $^{2}$${\mathit{D}}_{3/2}$) metastable states of ${\mathrm{Hg}}^{+}$ as well as of the 5${\mathit{d}}^{9}$6s${(}^{3}$${\mathit{D}}_{2}$) metastable state of ${\mathrm{Hg}}^{2+}$ have been measured by counting for equal time intervals either the 282-, 198-, or 217-nm photons emitted when the respective metastable ions decay to the ground state. The metastable Hg ions are produced inside a cylindrical electrostatic ion trap by electron bombardment of background Hg vapor maintained at pressures ranging from 4 to 50\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}8}$ Torr. The trap consists of a 5.0-cm-diam, 7.5-cm-long cylinder with end caps plus a concentric 0.003-cm-diam central cylinder maintained at a negative potential of 140 V. Following electron impact of the Hg vapor, some of the photons emitted by the decaying metastable ion population are focused onto a narrow-bandwidth interference filter. The photons transmitted by the filter are detected by a photomultiplier tube as a function of time and generate a decay curve. However, the signal detected with the interference filter used to monitor the $^{2}$${\mathit{D}}_{3/2}$ metastable-state population consists of two exponentially decaying components, indicating the presence of another metastable state decaying through the emission of a photon within the bandpass of the filter. The second component is assumed to arise from a cascade originating with the 5${\mathit{d}}^{9}$6s6p (J=9/2) metastable state of ${\mathrm{Hg}}^{+}$. Therefore, as dictated by the composition of the photon decay curve, the pressure-dependent decay rates of the metastable states are obtained from a least-squares fit of either a single- or double-component exponential decay to the natural logarithm of the decay curve.Mean decay rates extrapolated to zero pressure of the background Hg vapor using a straight-line least-squares fit, and the inverse of the zero-pressure intercept yields the natural radiative lifetime of the relevant metastable state. Our results for the lifetimes of the $^{2}$${\mathit{D}}_{5/2}$, $^{2}$${\mathit{D}}_{3/2}$, and J=9/2 metastable states of ${\mathrm{Hg}}^{+}$ are 87\ifmmode\pm\else\textpm\fi{}4, 8.8\ifmmode\pm\else\textpm\fi{}0.4, and 60\ifmmode\pm\else\textpm\fi{}6 msec, respectively, while the lifetime of the ${\mathrm{Hg}}^{2+}$ ${(}^{3}$${\mathit{D}}_{2}$) metastable state is 34\ifmmode\pm\else\textpm\fi{}3 msec.

Physical Review ANov 1, 199020 citations

Measurement of the branching fractions and lifetime of the 5D5/2 level of Ba+

Carolyn Auchter, Thomas W. Noel, Matthew Hoffman +2 more

We present a measurement of the branching fractions for decay from the long-lived $5{D}_{5/2}$ level in ${^{138}\mathrm{Ba}}^{+}$ . The branching fraction for decay into the $6{S}_{1/2}$ ground state was found to be $0.846{(25)}_{\mathrm{stat}}{(4)}_{\mathrm{sys}}$ . We also report an improved measurement of the $5{D}_{5/2}$ lifetime, ${\ensuremath{\tau}}_{5{D}_{5/2}}=31.2(0.9)$ s. Together these measurements provide an experimental determination of transition rates for decay out of the $5{D}_{5/2}$ level. The low ($<7\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}12}$ Torr) pressure in the ion trap in which these measurements were made simplified data acquisition and analysis. Comparison of the experimental results with theoretical predictions of the transition rates shows good agreement.We present a measurement of the branching fractions for decay from the long-lived $5{D}_{5/2}$ level in ${^{138}\mathrm{Ba}}^{+}$. The branching fraction for decay into the $6{S}_{1/2}$ ground state was found to be $0.846{(25)}_{\mathrm{stat}}{(4)}_{\mathrm{sys}}$. We also report an improved measurement of the $5{D}_{5/2}$ lifetime, ${\ensuremath{\tau}}_{5{D}_{5/2}}=31.2(0.9)$ s. Together these measurements provide an experimental determination of transition rates for decay out of the $5{D}_{5/2}$ level. The low ($<7\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}12}$ Torr) pressure in the ion trap in which these measurements were made simplified data acquisition and analysis. Comparison of the experimental results with theoretical predictions of the transition rates shows good agreement.

arXiv:1409.0873Physical Review ADec 17, 201426 citations

\tau _{D_{5/2}} = 26.4(1.7)

s is obtained through extrapolation to zero residual gas pressure.

A single

{\mathrm{Ba}}^{+}

atom was confined in a radio-frequency ion trap and cooled by near-resonant laser light. Quantum jumps into and out of the metastable 5d

^{2}D_{5/2}

level were observed that followed the expected exponential distribution in dark periods to good agreement. Measurement of quantum-jump distributions together with careful measurements of the absolute partial pressures of all residual gas species enabled accurate measurements of the quenched 5d

^{2}D_{5/2}

lifetime as a function of quenching gas pressure. Measurements of quenching were observed at pressures where the mean collision rate was on the order of 1 ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$. The results yielded quenching rate constants for the metastable level for a series of gases that typically make up the residual gas environment of ultra-high-vacuum systems (

{\mathrm{H}}_{2}

, He,

{\mathrm{CH}}_{4}

{\mathrm{H}}_{2}

O, CO,

{\mathrm{N}}_{2}

, Ar, and

{\mathrm{CO}}_{2}

) together with an improved value of the

{5}^{2}

{\mathrm{D}}_{5/2}

radiative lifetime of

{t}_{0}

=34.5\ifmmode\pm\else\textpm\fi{}3.5 s. The above quenching rate constants were then compared with classical ion-molecule collision theory. It was found that the quenching rates for molecular gases were comparable to the classical collision rates, while the rates for atomic gases were considerably lower.

The natural lifetime of the metastable

4d\phantom{\rule{0.2em}{0ex}}^{2}D_{5∕2}

state in

^{88}\mathrm{Sr}^{+}

has been measured using a single laser-cooled, trapped ion. The ion was prepared in the

4d\phantom{\rule{0.2em}{0ex}}^{2}D_{5∕2}

state by laser excitation of the $5s\phantom{\rule{0.2em}{0ex}}^{2}S_{1∕2}\ensuremath{-}4d\phantom{\rule{0.2em}{0ex}}^{2}D_{5∕2}$ quadrupole transition at 674 nm. The decay time was measured by using Dehmelt's electron shelving method to monitor the ion's electronic state. Two separate investigations were conducted under slightly different experimental conditions. 160 000 decay times from the

4d\phantom{\rule{0.2em}{0ex}}^{2}D_{5∕2}

state were observed in total, and two different methods for determining the statistical value of the measured lifetime have been compared. Systematic effects have also been estimated, and including these effects yields a value of $\ensuremath{\tau}=390.8(1.6)\phantom{\rule{0.3em}{0ex}}\mathrm{ms}$ ($1\ensuremath{\sigma}$ uncertainty) for the natural lifetime.

The extremely long lifetimes of the metastable

D

states of the

{\mathrm{Ba}}^{+}

ion make it difficult to measure them accurately due to their high sensitivity to collisional effects. Thus a discrepancy exists between theories and experiments for the

{\mathrm{Ba}}^{+}

{D}_{3/2}

state. We have measured the

{D}_{3/2}

lifetime under a nearly ideal condition, i.e., single trapped

{\mathrm{Ba}}^{+}

ions in ultrahigh vacuum. The obtained value of $79.8\ifmmode\pm\else\textpm\fi{}4.6\mathrm{s}$ resolves the existing discrepancy. The collisional quenching is found insignificant in our experiment, but there are indications of a non-negligible fine-structure mixing effect.

We report a measurement of the lifetime of the

3d{}^{2}{D}_{5/2}

metastable level in

{}^{40}{\mathrm{Ca}}^{+},

using quantum jumps of a single cold calcium ion in a linear Paul trap. The

4s{}^{2}{S}_{1/2}--3d{}^{2}{D}_{5/2}

transition is significant for single-ion optical frequency standards, astrophysical references, and tests of atomic structure calculations. We obtain $\ensuremath{\tau}=1.168\ifmmode\pm\else\textpm\fi{}0.007$ s from observation of nearly

64000

quantum jumps during $\ensuremath{\sim}32$ h. Our result is more precise and significantly larger than previous measurements. Experiments carried out to quantify systematic effects included a study of a previously unremarked source of systematic error, namely, excitation by the broad background of radiation emitted by a semiconductor diode laser. Combining our result with atomic structure calculations yields $1.20\ifmmode\pm\else\textpm\fi{}0.01$ s for the lifetime of

3d{}^{2}{D}_{3/2}.

We also use quantum jump observations to demonstrate photon antibunching, and to estimate background pressure and heating rates in the ion trap.

The natural radiative lifetimes of the 5${\mathit{d}}^{9}

6

{\mathit{s}}^{2}$

{(}^{2}

{\mathit{D}}_{5/2}

and

^{2}

{\mathit{D}}_{3/2}

) metastable states of

{\mathrm{Hg}}^{+}

as well as of the 5${\mathit{d}}^{9}

6s

{(}^{3}$${\mathit{D}}_{2}$) metastable state of ${\mathrm{Hg}}^{2+}$ have been measured by counting for equal time intervals either the 282-, 198-, or 217-nm photons emitted when the respective metastable ions decay to the ground state. The metastable Hg ions are produced inside a cylindrical electrostatic ion trap by electron bombardment of background Hg vapor maintained at pressures ranging from 4 to 50\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}8}$ Torr. The trap consists of a 5.0-cm-diam, 7.5-cm-long cylinder with end caps plus a concentric 0.003-cm-diam central cylinder maintained at a negative potential of 140 V. Following electron impact of the Hg vapor, some of the photons emitted by the decaying metastable ion population are focused onto a narrow-bandwidth interference filter. The photons transmitted by the filter are detected by a photomultiplier tube as a function of time and generate a decay curve. However, the signal detected with the interference filter used to monitor the $^{2}$${\mathit{D}}_{3/2}$ metastable-state population consists of two exponentially decaying components, indicating the presence of another metastable state decaying through the emission of a photon within the bandpass of the filter. The second component is assumed to arise from a cascade originating with the 5${\mathit{d}}^{9}$6s6p (J=9/2) metastable state of

{\mathrm{Hg}}^{+}

. Therefore, as dictated by the composition of the photon decay curve, the pressure-dependent decay rates of the metastable states are obtained from a least-squares fit of either a single- or double-component exponential decay to the natural logarithm of the decay curve.Mean decay rates extrapolated to zero pressure of the background Hg vapor using a straight-line least-squares fit, and the inverse of the zero-pressure intercept yields the natural radiative lifetime of the relevant metastable state. Our results for the lifetimes of the

^{2}

{\mathit{D}}_{5/2}

^{2}

{\mathit{D}}_{3/2}

, and J=9/2 metastable states of

{\mathrm{Hg}}^{+}

are 87\ifmmode\pm\else\textpm\fi{}4, 8.8\ifmmode\pm\else\textpm\fi{}0.4, and 60\ifmmode\pm\else\textpm\fi{}6 msec, respectively, while the lifetime of the

{\mathrm{Hg}}^{2+}

{(}^{3}

{\mathit{D}}_{2}

) metastable state is 34\ifmmode\pm\else\textpm\fi{}3 msec.

We present a measurement of the branching fractions for decay from the long-lived

5{D}_{5/2}

level in

{^{138}\mathrm{Ba}}^{+}

. The branching fraction for decay into the

6{S}_{1/2}

ground state was found to be

0.846{(25)}_{\mathrm{stat}}{(4)}_{\mathrm{sys}}

. We also report an improved measurement of the

5{D}_{5/2}

lifetime, ${\ensuremath{\tau}}_{5{D}_{5/2}}=31.2(0.9)$ s. Together these measurements provide an experimental determination of transition rates for decay out of the

5{D}_{5/2}

level. The low ($<7\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}12}$ Torr) pressure in the ion trap in which these measurements were made simplified data acquisition and analysis. Comparison of the experimental results with theoretical predictions of the transition rates shows good agreement.