Physical Review A

Collision energy pooling for Sr(5 3 PJ )+Sr(5 J’3 ) → Sr(6 3,1 S)+Sr(5 1 S)

James Floyd Kelly, Martin A. Harris, Alan C. Gallagher

Published Aug 1, 1988• 36 citations

Abstract

Energy pooling (EP) has been observed in Sr vapor following pulsed optical excitation to the 5${}^{3}$${P}_{1}$ state. From the time-dependent radiative decay of 6${}^{3}$${S}_{1}$ and of ${6}^{1}$${\mathit{S}}_{0}$ via the cascade resonance line, the EP rate coefficients have been investigated for the following: Sr(5 $^{3}P_{J}$)+Sr(5${}^{3}$${\mathit{P}}_{\mathit{J}\mathcal{'}}$) ${(5}^{1}$${S}_{0}$) +Sr(6 $^{3}S_{1}$ or ${6}^{1}$${S}_{0}$). The values of ${k}_{11}$ have been measured, as well as ${k}_{\mathrm{JJ}\mathcal{'}}$ averaged over a thermal distribution of 5 $^{3}P_{J}$ populations. The time-dependent Sr(${5}^{3}$${P}_{J}$) densities were measured by absorption of lines from a Sr lamp crossing the excitation region. The rate coefficients are surprisingly large; in spite of the small statistical weights of these product states, they are nearly gas-kinetic. The dependence of the rates upon spin, J, and energy defect \ensuremath{\Delta}E has also been examined.

DOI: 10.1103/physreva.38.1225

Related papers

Collisional energy transfer between excited Sr atoms

H. G. C. Werij, Martin A. Harris, J. Cooper +2 more

Physical Review AMar 1, 199121 citations

Energy-pooling collisions in cesium: 6 PJ +6 PJ →6S+(nl=7P,6D,8S,4F)

Z. J. Jabbour, R. K. Namiotka, John Huennekens +3 more

Physical Review AAug 1, 199663 citations

[Collisional energy transfer between excited Rb atoms].

Hongping Wu, Qi-cun Guo, Kang Dai +1 more

Aug 1, 20091 citation

Kinetic investigation of energy pooling from Sr [5s5p(3P J )] studied by time-resolved atomic emission following pulsed dye-laser excitation

David Husain, Jie Hong Lei

Journal of the Chemical Society Faraday TransactionsJan 1, 19953 citations

Velocity dependence of energy pooling collisions in strontium

Jonathan Andrew Neuman, J. Cooper, Alan C. Gallagher

Physical Review AJul 1, 19975 citations

Energy-pooling collisions in barium

Jonathan Andrew Neuman, Alan C. Gallagher, J. Cooper

Physical Review AAug 1, 199420 citations

Physical Review A

Collision energy pooling for Sr(5 3 PJ )+Sr(5 J’3 ) → Sr(6 3,1 S)+Sr(5 1 S)

James Floyd Kelly, Martin A. Harris, Alan C. Gallagher

Published Aug 1, 1988• 36 citations

Publisher

Abstract

Energy pooling (EP) has been observed in Sr vapor following pulsed optical excitation to the 5

{}^{3}$${P}_{1}

state. From the time-dependent radiative decay of 6

{}^{3}$${S}_{1}

and of

{6}^{1}$${\mathit{S}}_{0}

via the cascade resonance line, the EP rate coefficients have been investigated for the following: Sr(5

^{3}P_{J}

)+Sr(5

{}^{3}$${\mathit{P}}_{\mathit{J}\mathcal{'}}

)

{(5}^{1}$${S}_{0}

) +Sr(6

^{3}S_{1}

{6}^{1}$${S}_{0}

). The values of

{k}_{11}

have been measured, as well as

{k}_{\mathrm{JJ}\mathcal{'}}

averaged over a thermal distribution of 5

^{3}P_{J}

populations. The time-dependent Sr(

{5}^{3}$${P}_{J}

) densities were measured by absorption of lines from a Sr lamp crossing the excitation region. The rate coefficients are surprisingly large; in spite of the small statistical weights of these product states, they are nearly gas-kinetic. The dependence of the rates upon spin, J, and energy defect \ensuremath{\Delta}E has also been examined.

DOI: 10.1103/physreva.38.1225

Related papers

Collisional energy transfer between excited Sr atoms

H. G. C. Werij, Martin A. Harris, J. Cooper +2 more

The following energy-transfer reactions have been observed in a Sr vapor following pulsed excitation of the 5 $^{1}$ ${\mathit{P}}_{1}$ state: ${\mathrm{Sr}}^{\mathrm{*}}$ (5 $^{1}$ ${\mathit{P}}_{1}$ )+ ${\mathrm{Sr}}^{\mathrm{*}}$ (5 $^{1}$ ${\mathit{P}}_{1}$ )\ensuremath{\rightarrow}Sr(5 $^{1}$ ${\mathit{S}}_{0}$ )+ ${\mathrm{Sr}}^{\mathrm{*}\mathrm{*}}$ ( ${\mathit{n}}^{2\mathit{S}+1}$ L)-\ensuremath{\Delta}E, ${\mathrm{Sr}}^{\mathrm{*}}$ (4 $^{1}$ ${\mathit{D}}_{2}$ ) + ${\mathrm{Sr}}^{\mathrm{*}}$ (4 $^{1}$ ${\mathit{D}}_{2}$ )\ensuremath{\rightarrow}Sr(5 $^{1}$ ${\mathit{S}}_{0}$ )+ ${\mathrm{Sr}}^{\mathrm{*}\mathrm{*}}$ ( ${\mathit{n}}^{2\mathit{S}+1}$ L)-\ensuremath{\Delta}E. The 4 $^{1}$ ${\mathit{D}}_{2}$ state was populated by a nonlinear stimulated process. By measuring the rate coefficients for these reactions for over 40 final states ${\mathit{n}}^{2\mathit{S}+1}$ L, we look for insight into how these reactions depend on energy defect, spin, and angular momentum. It is found that there is not a very strong dependence on the energy defect, and that singlet and triplet final states are produced in comparable amounts. The final states tend to be populated more effectively as their angular momentum increases. Total rate coefficients are of the order of gas-kinetic rates.The following energy-transfer reactions have been observed in a Sr vapor following pulsed excitation of the 5 $^{1}$${\mathit{P}}_{1}$ state: ${\mathrm{Sr}}^{\mathrm{*}}$(5 $^{1}$${\mathit{P}}_{1}$)+${\mathrm{Sr}}^{\mathrm{*}}$(5 $^{1}$${\mathit{P}}_{1}$)\ensuremath{\rightarrow}Sr(5 $^{1}$${\mathit{S}}_{0}$)+${\mathrm{Sr}}^{\mathrm{*}\mathrm{*}}$(${\mathit{n}}^{2\mathit{S}+1}$L)-\ensuremath{\Delta}E, ${\mathrm{Sr}}^{\mathrm{*}}$(4 $^{1}$${\mathit{D}}_{2}$) +${\mathrm{Sr}}^{\mathrm{*}}$(4 $^{1}$${\mathit{D}}_{2}$)\ensuremath{\rightarrow}Sr(5 $^{1}$${\mathit{S}}_{0}$)+${\mathrm{Sr}}^{\mathrm{*}\mathrm{*}}$(${\mathit{n}}^{2\mathit{S}+1}$L)-\ensuremath{\Delta}E. The 4 $^{1}$${\mathit{D}}_{2}$ state was populated by a nonlinear stimulated process. By measuring the rate coefficients for these reactions for over 40 final states ${\mathit{n}}^{2\mathit{S}+1}$L, we look for insight into how these reactions depend on energy defect, spin, and angular momentum. It is found that there is not a very strong dependence on the energy defect, and that singlet and triplet final states are produced in comparable amounts. The final states tend to be populated more effectively as their angular momentum increases. Total rate coefficients are of the order of gas-kinetic rates.

Physical Review AMar 1, 199121 citations

Energy-pooling collisions in cesium: 6 PJ +6 PJ →6S+(nl=7P,6D,8S,4F)

Z. J. Jabbour, R. K. Namiotka, John Huennekens +3 more

We report experimental rate coefficients for the energy-pooling collisions Cs(6 ${\mathit{P}}_{1/2}$ )+Cs(6 ${\mathit{P}}_{1/2}$ )\ensuremath{\rightarrow}Cs(6 ${\mathit{S}}_{1/2}$ )+Cs(${\mathit{nl}}_{\mathit{J}\ensuremath{'}}$) and Cs(6 ${\mathit{P}}_{3/2}$ )+Cs(6 ${\mathit{P}}_{3/2}$ )\ensuremath{\rightarrow}Cs(6 ${\mathit{S}}_{1/2}$ )+Cs(${\mathit{nl}}_{\mathit{J}\ensuremath{'}}$) where ${\mathit{nl}}_{\mathit{J}\ensuremath{'}}$=7 ${\mathit{P}}_{1/2}$ , 7 ${\mathit{P}}_{3/2}$ , 6 ${\mathit{D}}_{3/2}$ , 6 ${\mathit{D}}_{5/2}$ , 8 ${\mathit{S}}_{1/2}$ , 4 ${\mathit{F}}_{5/2}$ , or 4 ${\mathit{F}}_{7/2}$ . Atoms were excited to either the 6 ${\mathit{P}}_{1/2}$ or 6 ${\mathit{P}}_{3/2}$ state using a single-mode Ti:sapphire laser. The excited-atom density and spatial distribution were mapped by monitoring the absorption of a counterpropagating single-mode ring dye laser beam, tuned to either the 6 ${\mathit{P}}_{1/2}$ \ensuremath{\rightarrow}8 ${\mathit{S}}_{1/2}$ or 6 ${\mathit{P}}_{3/2}$ \ensuremath{\rightarrow}7 ${\mathit{D}}_{3/2,5/2}$ transitions, which could be translated parallel to the pump beam. Transmission factors, which describe the average probability that photons emitted within the fluorescence detection region can pass through the optically thick vapor without being absorbed, were calculated for all relevant transitions. Effective lifetimes of levels populated by energy-pooling collisions are modified by radiation trapping, and these factors were calculated using the Molisch theory. These calculated quantities have been combined with the measured excited-atom densities and fluorescence ratios to yield absolute energy-pooling rate coefficients. It was found that the rate for production, in all cases, is greatest for 6D, but that 1/2-1/2 collisions are significantly more efficient than 3/2-3/2 collisions for populating 7P. It was also found that 7 ${\mathit{P}}_{1/2}$ is populated two to three times more efficiently than 7 ${\mathit{P}}_{3/2}$ in 1/2-1/2 collisions, but that the 7P fine-structure levels are approximately equally populated in 3/2-3/2 collisions. \textcopyright{} 1996 The American Physical Society.We report experimental rate coefficients for the energy-pooling collisions Cs(6${\mathit{P}}_{1/2}$)+Cs(6${\mathit{P}}_{1/2}$)\ensuremath{\rightarrow}Cs(6${\mathit{S}}_{1/2}$)+Cs(${\mathit{nl}}_{\mathit{J}\ensuremath{'}}$) and Cs(6${\mathit{P}}_{3/2}$)+Cs(6${\mathit{P}}_{3/2}$)\ensuremath{\rightarrow}Cs(6${\mathit{S}}_{1/2}$)+Cs(${\mathit{nl}}_{\mathit{J}\ensuremath{'}}$) where ${\mathit{nl}}_{\mathit{J}\ensuremath{'}}$=7${\mathit{P}}_{1/2}$, 7${\mathit{P}}_{3/2}$, 6${\mathit{D}}_{3/2}$, 6${\mathit{D}}_{5/2}$, 8${\mathit{S}}_{1/2}$, 4${\mathit{F}}_{5/2}$, or 4${\mathit{F}}_{7/2}$. Atoms were excited to either the 6${\mathit{P}}_{1/2}$ or 6${\mathit{P}}_{3/2}$ state using a single-mode Ti:sapphire laser. The excited-atom density and spatial distribution were mapped by monitoring the absorption of a counterpropagating single-mode ring dye laser beam, tuned to either the 6${\mathit{P}}_{1/2}$\ensuremath{\rightarrow}8${\mathit{S}}_{1/2}$ or 6${\mathit{P}}_{3/2}$\ensuremath{\rightarrow}7${\mathit{D}}_{3/2,5/2}$ transitions, which could be translated parallel to the pump beam. Transmission factors, which describe the average probability that photons emitted within the fluorescence detection region can pass through the optically thick vapor without being absorbed, were calculated for all relevant transitions. Effective lifetimes of levels populated by energy-pooling collisions are modified by radiation trapping, and these factors were calculated using the Molisch theory. These calculated quantities have been combined with the measured excited-atom densities and fluorescence ratios to yield absolute energy-pooling rate coefficients. It was found that the rate for production, in all cases, is greatest for 6D, but that 1/2-1/2 collisions are significantly more efficient than 3/2-3/2 collisions for populating 7P. It was also found that 7${\mathit{P}}_{1/2}$ is populated two to three times more efficiently than 7${\mathit{P}}_{3/2}$ in 1/2-1/2 collisions, but that the 7P fine-structure levels are approximately equally populated in 3/2-3/2 collisions. \textcopyright{} 1996 The American Physical Society.

Physical Review AAug 1, 199663 citations

[Collisional energy transfer between excited Rb atoms].

Hongping Wu, Qi-cun Guo, Kang Dai +1 more

Energy pooling (EP) was observed in Rb vapor following pulsed optical excitation to the 5P1/2 state. The 5P3/2 state was populated by the energy transfer process: Rb(5P1/2)+Rb(5S1/2) --> Rb(5P3/2)+Rb(5Sl/2). The resulting densities of Rb atoms at the 5P1/2 level were obtained from the absorption of narrow spectral line from a Rb hollow cathode lamp, connecting the 5P1/2 state to 7S state. Since the effective lifetimes of the 5P1/2 and 5P3/2 states are approximately equal, the densities of the 5P3/2 level were obtained from the D2 to D1 fluorescence ratios where D1 and D2 are lines of the 5P1/2 --> 5S1/2 and 5P3/2 --> 5S1/2 transition. Because the time of the fine structure exchanging is much shorter than the lifetime of the 5D state, the fluorescence originating from the 5D state produced by the 5P1/2 + 5P3/2 and 5P3/2 + 5P3/2 processes follows the instantaneous production rate of the 5P1/2 + 5P1/2 process. It is clear that 5P/2 + 5P3/2 and 5P3/2 + 5P3/2 collisions can significantly influence the results obtained for the 5P1/2 + 5P1/2 rate since the energy defect for 5D state is much smaller for 5P1/2 + 5P3/2 and 5P3/2 + 5P3/2 collisions than for 5P1/2 + 5P1/2 collisions. Effective lifetimes of the 5P levels were calculated using radiation trapping theory. The time-integrated populations and signals were studied and analyzed. The resulting fluorescence included the direct component emitted in the decay of the optically excited 5P1/2 state and the sensitized component arising from the collisions for populating 5D state at different cell temperature. These relative intensities were combined with the measured excited atom densities to yield absolute energy-pooling rate coefficients. The cross sections (in units of 10(-14) cm2) for the energy-pooling collisions [i. e. , 5P1/2 + 5P1/2, 5P1/2 + 5P3/2, 5P3/2 + 5P3/2] are 0.78, 2.9 and 3.1, respectively. The dependence of the rates upon energy defect deltaE was examined, but the 5D3/2 level was approximately equally populated in 5P3/2 + 5P3/2 (deltaE = 68 cm(-1)) and 5P3/2 + 5P1/2 (deltaE = 306 cm(-1)) collisions. The 5P1/2 + 5P3/2 collisions are as efficient as 5P3/2 + 5P3/2 for populating 5D3/2 state.Energy pooling (EP) was observed in Rb vapor following pulsed optical excitation to the 5P1/2 state. The 5P3/2 state was populated by the energy transfer process: Rb(5P1/2)+Rb(5S1/2) --> Rb(5P3/2)+Rb(5Sl/2). The resulting densities of Rb atoms at the 5P1/2 level were obtained from the absorption of narrow spectral line from a Rb hollow cathode lamp, connecting the 5P1/2 state to 7S state. Since the effective lifetimes of the 5P1/2 and 5P3/2 states are approximately equal, the densities of the 5P3/2 level were obtained from the D2 to D1 fluorescence ratios where D1 and D2 are lines of the 5P1/2 --> 5S1/2 and 5P3/2 --> 5S1/2 transition. Because the time of the fine structure exchanging is much shorter than the lifetime of the 5D state, the fluorescence originating from the 5D state produced by the 5P1/2 + 5P3/2 and 5P3/2 + 5P3/2 processes follows the instantaneous production rate of the 5P1/2 + 5P1/2 process. It is clear that 5P/2 + 5P3/2 and 5P3/2 + 5P3/2 collisions can significantly influence the results obtained for the 5P1/2 + 5P1/2 rate since the energy defect for 5D state is much smaller for 5P1/2 + 5P3/2 and 5P3/2 + 5P3/2 collisions than for 5P1/2 + 5P1/2 collisions. Effective lifetimes of the 5P levels were calculated using radiation trapping theory. The time-integrated populations and signals were studied and analyzed. The resulting fluorescence included the direct component emitted in the decay of the optically excited 5P1/2 state and the sensitized component arising from the collisions for populating 5D state at different cell temperature. These relative intensities were combined with the measured excited atom densities to yield absolute energy-pooling rate coefficients. The cross sections (in units of 10(-14) cm2) for the energy-pooling collisions [i. e. , 5P1/2 + 5P1/2, 5P1/2 + 5P3/2, 5P3/2 + 5P3/2] are 0.78, 2.9 and 3.1, respectively. The dependence of the rates upon energy defect deltaE was examined, but the 5D3/2 level was approximately equally populated in 5P3/2 + 5P3/2 (deltaE = 68 cm(-1)) and 5P3/2 + 5P1/2 (deltaE = 306 cm(-1)) collisions. The 5P1/2 + 5P3/2 collisions are as efficient as 5P3/2 + 5P3/2 for populating 5D3/2 state.

Aug 1, 20091 citation

Kinetic investigation of energy pooling from Sr [5s5p(3P J )] studied by time-resolved atomic emission following pulsed dye-laser excitation

David Husain, Jie Hong Lei

A kinetic investigation is presented of energy pooling arising from self-annihilation of the optically metastable state, Sr[5s5p(3PJ)], generated by pulsed dye-laser excitation of strontium vapour at λ= 689.3 nm {Sr[5s5p(3P1)]â†� Sr[5s2(1S0)]} at elevated temperature in the presence of excess helium buffer gas. Time-resolved emission was observed for a number of energy-pooled states, namely, Sr[5s5p(1P1)], Sr[5s6s(3S1)], Sr[4d5p(3F2, 3, 4)], Sr[4d5p(1D2)], Sr[5s6p(3P1, 2)], Sr[5s5d(3D2)] and Sr[5p2(3P2)]. This includes characterisation of the time profiles from specific spin–orbit states and significantly extends the range of atomic pooled states reported hitherto derived from the 5s5p(3PJ) energy store. Following rapid energy pooling, the profiles of the ‘pool’ and ‘store’ states are shown to be exponential in character and the first-order decay coefficients are found to be in the ratio of 2 ∶ 1 within experimental error. Further, using the appropriate sensitivity calibration of the optical system, the variation of the ratio of the integrated atomic emission intensities of the energy pooled states to that of the energy store itself were found to be linear and in accord with a mechanism for energy pooling in each case arising from 3PJ+3PJ self-annihilation. The normalised, integrated emission intensities of the energy-pooled states which involved population via endothermic processes from Sr(3PJ)+ Sr(3PJ) were determined and used to calculate the relative distributions of the energy-pooled states on collision. These were plotted semi-logarithmically as a function of the electronic state energy of the appropriate state and yielded a Boltzmann temperature higher than the ambient temperature employed, reflecting the role of atomic collisions with high kinetic energies on energy pooling.A kinetic investigation is presented of energy pooling arising from self-annihilation of the optically metastable state, Sr[5s5p(3PJ)], generated by pulsed dye-laser excitation of strontium vapour at λ= 689.3 nm {Sr[5s5p(3P1)]â†� Sr[5s2(1S0)]} at elevated temperature in the presence of excess helium buffer gas. Time-resolved emission was observed for a number of energy-pooled states, namely, Sr[5s5p(1P1)], Sr[5s6s(3S1)], Sr[4d5p(3F2, 3, 4)], Sr[4d5p(1D2)], Sr[5s6p(3P1, 2)], Sr[5s5d(3D2)] and Sr[5p2(3P2)]. This includes characterisation of the time profiles from specific spin–orbit states and significantly extends the range of atomic pooled states reported hitherto derived from the 5s5p(3PJ) energy store. Following rapid energy pooling, the profiles of the ‘pool’ and ‘store’ states are shown to be exponential in character and the first-order decay coefficients are found to be in the ratio of 2 ∶ 1 within experimental error. Further, using the appropriate sensitivity calibration of the optical system, the variation of the ratio of the integrated atomic emission intensities of the energy pooled states to that of the energy store itself were found to be linear and in accord with a mechanism for energy pooling in each case arising from 3PJ+3PJ self-annihilation. The normalised, integrated emission intensities of the energy-pooled states which involved population via endothermic processes from Sr(3PJ)+ Sr(3PJ) were determined and used to calculate the relative distributions of the energy-pooled states on collision. These were plotted semi-logarithmically as a function of the electronic state energy of the appropriate state and yielded a Boltzmann temperature higher than the ambient temperature employed, reflecting the role of atomic collisions with high kinetic energies on energy pooling.

Journal of the Chemical Society Faraday TransactionsJan 1, 19953 citations

Velocity dependence of energy pooling collisions in strontium

Jonathan Andrew Neuman, J. Cooper, Alan C. Gallagher

The threshold behavior of the cross section of an endothermic energy pooling reaction is investigated. In a vapor cell experiment, pulsed excitation followed by delayed fluorescence detection narrows the transverse velocity distribution of colliding pairs of laser-excited strontium atoms in the ${5s5p}^{3}{P}_{1}$ level, and laser detuning establishes the collision velocity in the direction of counterpropagating laser beams. A probe laser detects the excited-state collision product of the endothermic ${5s5p}^{3}{P}_{1}{+5s5p}^{3}{P}_{1}\ensuremath{\rightarrow}{5s6s}^{1}{S}_{0}{+5s}^{21}{S}_{0}$ reaction. The cross section rises steeply at threshold and is nearly flat for 1.2--2 times the threshold energy. This behavior can be partly explained by the shape of the molecular potential curve of the collisionally produced state. From the measured $1.1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}12}{\mathrm{cm}}^{3}{\mathrm{}\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$ thermally averaged rate coefficient, the above-threshold cross section is found to be approximately $6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}17}{\mathrm{cm}}^{2}.$ The thermally averaged rate coefficient for the highly exothermic energy pooling reaction ${5s5p}^{3}{P}_{1}{+5s5p}^{3}{P}_{1}\ensuremath{\rightarrow}{5s5p}^{1}{P}_{1}{+5s}^{21}{S}_{0}$ is also reported and measured to be $1.1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}{\mathrm{cm}}^{3}{\mathrm{}\mathrm{s}}^{\mathrm{\ensuremath{-}}1}.$ The cross section for this exothermic reaction is found to be nearly independent of collision velocity.The threshold behavior of the cross section of an endothermic energy pooling reaction is investigated. In a vapor cell experiment, pulsed excitation followed by delayed fluorescence detection narrows the transverse velocity distribution of colliding pairs of laser-excited strontium atoms in the ${5s5p}^{3}{P}_{1}$ level, and laser detuning establishes the collision velocity in the direction of counterpropagating laser beams. A probe laser detects the excited-state collision product of the endothermic ${5s5p}^{3}{P}_{1}{+5s5p}^{3}{P}_{1}\ensuremath{\rightarrow}{5s6s}^{1}{S}_{0}{+5s}^{21}{S}_{0}$ reaction. The cross section rises steeply at threshold and is nearly flat for 1.2--2 times the threshold energy. This behavior can be partly explained by the shape of the molecular potential curve of the collisionally produced state. From the measured $1.1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}12}{\mathrm{cm}}^{3}{\mathrm{}\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$ thermally averaged rate coefficient, the above-threshold cross section is found to be approximately $6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}17}{\mathrm{cm}}^{2}.$ The thermally averaged rate coefficient for the highly exothermic energy pooling reaction ${5s5p}^{3}{P}_{1}{+5s5p}^{3}{P}_{1}\ensuremath{\rightarrow}{5s5p}^{1}{P}_{1}{+5s}^{21}{S}_{0}$ is also reported and measured to be $1.1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}{\mathrm{cm}}^{3}{\mathrm{}\mathrm{s}}^{\mathrm{\ensuremath{-}}1}.$ The cross section for this exothermic reaction is found to be nearly independent of collision velocity.

Physical Review AJul 1, 19975 citations

Energy-pooling collisions in barium

Jonathan Andrew Neuman, Alan C. Gallagher, J. Cooper

Rate coefficients for energy-pooling collisions between low-lying excited states of Ba have been measured. The 6s6p ${(}^{3}$ ${\mathit{P}}_{1}$ ) level in Ba is pumped by a cw diode laser, and radiative decay and collisions with buffer-gas atoms also populate the 5d6s ${(}^{1}$ D) and 5d6s ${(}^{3}$ D) metastable levels. The densities of these low-lying excited states are measured by the absorption of lines from a Ba hollow-cathode lamp, and the states populated by energy-pooling collisions are studied by comparing their fluorescence intensity to that of the laser-excited level. The rate coefficients are on the order of gas-kinetic rates, and they are not strongly dependent on energy defect, spin changes, or angular-momentum changes.Rate coefficients for energy-pooling collisions between low-lying excited states of Ba have been measured. The 6s6p${(}^{3}$${\mathit{P}}_{1}$) level in Ba is pumped by a cw diode laser, and radiative decay and collisions with buffer-gas atoms also populate the 5d6s${(}^{1}$D) and 5d6s${(}^{3}$D) metastable levels. The densities of these low-lying excited states are measured by the absorption of lines from a Ba hollow-cathode lamp, and the states populated by energy-pooling collisions are studied by comparing their fluorescence intensity to that of the laser-excited level. The rate coefficients are on the order of gas-kinetic rates, and they are not strongly dependent on energy defect, spin changes, or angular-momentum changes.

Physical Review AAug 1, 199420 citations

Energy pooling (EP) has been observed in Sr vapor following pulsed optical excitation to the 5

{}^{3}$${P}_{1}

state. From the time-dependent radiative decay of 6

{}^{3}$${S}_{1}

and of

{6}^{1}$${\mathit{S}}_{0}

via the cascade resonance line, the EP rate coefficients have been investigated for the following: Sr(5

^{3}P_{J}

)+Sr(5

{}^{3}$${\mathit{P}}_{\mathit{J}\mathcal{'}}

)

{(5}^{1}$${S}_{0}

) +Sr(6

^{3}S_{1}

{6}^{1}$${S}_{0}

). The values of

{k}_{11}

have been measured, as well as

{k}_{\mathrm{JJ}\mathcal{'}}

averaged over a thermal distribution of 5

^{3}P_{J}

populations. The time-dependent Sr(

{5}^{3}$${P}_{J}

The following energy-transfer reactions have been observed in a Sr vapor following pulsed excitation of the 5

^{1}

{\mathit{P}}_{1}

state:

{\mathrm{Sr}}^{\mathrm{*}}

^{1}

{\mathit{P}}_{1}

{\mathrm{Sr}}^{\mathrm{*}}

^{1}

{\mathit{P}}_{1}

)\ensuremath{\rightarrow}Sr(5

^{1}

{\mathit{S}}_{0}

{\mathrm{Sr}}^{\mathrm{*}\mathrm{*}}

(

{\mathit{n}}^{2\mathit{S}+1}

L)-\ensuremath{\Delta}E,

{\mathrm{Sr}}^{\mathrm{*}}

^{1}

{\mathit{D}}_{2}

) +

{\mathrm{Sr}}^{\mathrm{*}}

^{1}

{\mathit{D}}_{2}

)\ensuremath{\rightarrow}Sr(5

^{1}

{\mathit{S}}_{0}

{\mathrm{Sr}}^{\mathrm{*}\mathrm{*}}

(

{\mathit{n}}^{2\mathit{S}+1}

L)-\ensuremath{\Delta}E. The 4

^{1}

{\mathit{D}}_{2}

state was populated by a nonlinear stimulated process. By measuring the rate coefficients for these reactions for over 40 final states

{\mathit{n}}^{2\mathit{S}+1}

L, we look for insight into how these reactions depend on energy defect, spin, and angular momentum. It is found that there is not a very strong dependence on the energy defect, and that singlet and triplet final states are produced in comparable amounts. The final states tend to be populated more effectively as their angular momentum increases. Total rate coefficients are of the order of gas-kinetic rates.

We report experimental rate coefficients for the energy-pooling collisions Cs(6

{\mathit{P}}_{1/2}

)+Cs(6

{\mathit{P}}_{1/2}

)\ensuremath{\rightarrow}Cs(6

{\mathit{S}}_{1/2}

)+Cs(${\mathit{nl}}_{\mathit{J}\ensuremath{'}}$) and Cs(6

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

)+Cs(6

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

)\ensuremath{\rightarrow}Cs(6

{\mathit{S}}_{1/2}

)+Cs(${\mathit{nl}}_{\mathit{J}\ensuremath{'}}$) where ${\mathit{nl}}_{\mathit{J}\ensuremath{'}}$=7

{\mathit{P}}_{1/2}

, 7

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

, 6

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

, 6

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

, 8

{\mathit{S}}_{1/2}

, 4

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

, or 4

{\mathit{F}}_{7/2}

. Atoms were excited to either the 6

{\mathit{P}}_{1/2}

or 6

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

state using a single-mode Ti:sapphire laser. The excited-atom density and spatial distribution were mapped by monitoring the absorption of a counterpropagating single-mode ring dye laser beam, tuned to either the 6

{\mathit{P}}_{1/2}

\ensuremath{\rightarrow}8

{\mathit{S}}_{1/2}

or 6

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

\ensuremath{\rightarrow}7

{\mathit{D}}_{3/2,5/2}

transitions, which could be translated parallel to the pump beam. Transmission factors, which describe the average probability that photons emitted within the fluorescence detection region can pass through the optically thick vapor without being absorbed, were calculated for all relevant transitions. Effective lifetimes of levels populated by energy-pooling collisions are modified by radiation trapping, and these factors were calculated using the Molisch theory. These calculated quantities have been combined with the measured excited-atom densities and fluorescence ratios to yield absolute energy-pooling rate coefficients. It was found that the rate for production, in all cases, is greatest for 6D, but that 1/2-1/2 collisions are significantly more efficient than 3/2-3/2 collisions for populating 7P. It was also found that 7

{\mathit{P}}_{1/2}

is populated two to three times more efficiently than 7

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

in 1/2-1/2 collisions, but that the 7P fine-structure levels are approximately equally populated in 3/2-3/2 collisions. \textcopyright{} 1996 The American Physical Society.

{5s5p}^{3}{P}_{1}

level, and laser detuning establishes the collision velocity in the direction of counterpropagating laser beams. A probe laser detects the excited-state collision product of the endothermic ${5s5p}^{3}{P}_{1}{+5s5p}^{3}{P}_{1}\ensuremath{\rightarrow}{5s6s}^{1}{S}_{0}{+5s}^{21}{S}_{0}$ reaction. The cross section rises steeply at threshold and is nearly flat for 1.2--2 times the threshold energy. This behavior can be partly explained by the shape of the molecular potential curve of the collisionally produced state. From the measured $1.1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}12}{\mathrm{cm}}^{3}{\mathrm{}\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$ thermally averaged rate coefficient, the above-threshold cross section is found to be approximately $6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}17}{\mathrm{cm}}^{2}.$ The thermally averaged rate coefficient for the highly exothermic energy pooling reaction ${5s5p}^{3}{P}_{1}{+5s5p}^{3}{P}_{1}\ensuremath{\rightarrow}{5s5p}^{1}{P}_{1}{+5s}^{21}{S}_{0}$ is also reported and measured to be $1.1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}{\mathrm{cm}}^{3}{\mathrm{}\mathrm{s}}^{\mathrm{\ensuremath{-}}1}.$ The cross section for this exothermic reaction is found to be nearly independent of collision velocity.

Rate coefficients for energy-pooling collisions between low-lying excited states of Ba have been measured. The 6s6p

{(}^{3}

{\mathit{P}}_{1}

) level in Ba is pumped by a cw diode laser, and radiative decay and collisions with buffer-gas atoms also populate the 5d6s

{(}^{1}

D) and 5d6s

{(}^{3}

D) metastable levels. The densities of these low-lying excited states are measured by the absorption of lines from a Ba hollow-cathode lamp, and the states populated by energy-pooling collisions are studied by comparing their fluorescence intensity to that of the laser-excited level. The rate coefficients are on the order of gas-kinetic rates, and they are not strongly dependent on energy defect, spin changes, or angular-momentum changes.