We report experimental rate coefficients for the energy-pooling collisions Cs(6
P1/2)+Cs(6
P1/2)\ensuremath{\rightarrow}Cs(6
S1/2)+Cs(${\mathit{nl}}_{\mathit{J}\ensuremath{'}}$) and Cs(6
P3/2)+Cs(6
P3/2)\ensuremath{\rightarrow}Cs(6
S1/2)+Cs(${\mathit{nl}}_{\mathit{J}\ensuremath{'}}$) where ${\mathit{nl}}_{\mathit{J}\ensuremath{'}}$=7
P1/2, 7
P3/2, 6
D3/2, 6
D5/2, 8
S1/2, 4
F5/2, or 4
F7/2. Atoms were excited to either the 6
P1/2 or 6
P3/2 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
P1/2\ensuremath{\rightarrow}8
S1/2 or 6
P3/2\ensuremath{\rightarrow}7
D3/2,5/2 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
P1/2 is populated two to three times more efficiently than 7
P3/2 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 reverse heteronuclear energy-pooling collisions $\mathrm{K}(5D)+\mathrm{Na}(3S)\ensuremath{\rightarrow}\mathrm{K}(4P)+\mathrm{Na}(3P)$ and $\mathrm{K}(7S)+\mathrm{Na}(3S)\ensuremath{\rightarrow}\mathrm{K}(4P)+\mathrm{Na}(3P)$ at thermal energies. Both reactions are exothermic and very high rates were observed showing that reverse exothermic energy-pooling is an order of magnitude more efficient than the corresponding forward endothermic energy-pooling reactions. This is in accordance with the general behavior of the exothermic and endothermic energy-pooling rate coefficients in alkali-metal atoms. In the experiment the potassium atoms were excited in two steps to either the
5D or
7S state via the
4P level using two broadband cw dye lasers. A double-modulation technique has been used to select the fluorescence contributions at the
Na(3PJ) exit channels due only to the above reactions. The ground-state sodium and potassium atom densities were measured by the absorption of lines from a K-Na hollow-cathode lamp. The measured densities and fluorescence intensities have been used to obtain absolute reverse energy-pooling rate coefficients. The contribution to the rate coefficients from other processes are discussed.
We report experimental rate coefficients for the energy-pooling collisions Cs(6{ital P}{sub 1/2})+Cs(6{ital P}{sub 1/2}){r_arrow}Cs(6{ital S}{sub 1/2})+Cs({ital nl}{sub {ital J}{prime}}) and Cs(6{ital P}{sub 3/2})+Cs(6{ital P}{sub 3/2}){r_arrow}Cs(6{ital S}{sub 1/2})+Cs({ital nl}{sub {ital J}{prime}}) where {ital nl}{sub {ital J}{prime}}=7{ital P}{sub 1/2}, 7{ital P}{sub 3/2}, 6{ital D}{sub 3/2}, 6{ital D}{sub 5/2}, 8{ital S}{sub 1/2}, 4{ital F}{sub 5/2}, or 4{ital F}{sub 7/2}. Atoms were excited to either the 6{ital P}{sub 1/2} or 6{ital P}{sub 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{ital P}{sub 1/2}{r_arrow}8{ital S}{sub 1/2} or 6{ital P}{sub 3/2}{r_arrow}7{ital D}{sub 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 formore » production, in all cases, is greatest for 6{ital D}, but that 1/2-1/2 collisions are significantly more efficient than 3/2-3/2 collisions for populating 7{ital P}. It was also found that 7{ital P}{sub 1/2} is populated two to three times more efficiently than 7{ital P}{sub 3/2} in 1/2-1/2 collisions, but that the 7{ital P} fine-structure levels are approximately equally populated in 3/2-3/2 collisions. {copyright} {ital 1996 The American Physical Society.}« less
We report experimentally the measured rate coefficients for the energy pooling (EP) collisions process Cs(5D)+Cs(5D)-gCs(6S)+Cs(nL=9D,11S,7F) in cesium densities of 10^(16)-10^(17) cm^(-3). The 5D state was populated via 8S-g7P-g5D spontaneous emission following two-step pumping 6S-g6P_(3/2)-g8S. Since the 5D-g6P (3.0-3.6 microns) fluorescence could not be detected in this experiment, we carried out a relative measurement for the process 6P+5D-g6S+7D. The excited-atom density and spatial distribution were mapped by monitoring the absorption of a counterpropagating single-mode laser beam, tuned to 6P_(3/2)-g9S_(1/2) transition, which could be translated parallelly to the pump beam. The excited atom densities have been combined with the measured fluorescence ratios to yield EP rate coefficients. The average values for nL=9D,11S and 7F are 8.0+-4.0, 7.0+-3.5, and 9.3+-4.6 (in units of 10^(-10) cm3/s), respectively. Influence of the energy transfer process 11S+6S-g7F+6S on the rate coefficients k_(11S) and k_(7F) is also discussed.
Rate coefficients for energy-pooling (EP) collisions Rb(5P_(J))+Cs(6P_(3/2))-->Rb(5S_(1/2))+Cs(nl_(J')) have been measured. Atoms were excited to Rb(5P_(J)) and Cs(6P_(3/2)) states using two single-mode diode lasers. To isolate the heteronuclear contribution in the fluorescence spectrum, a double-modulation technique has been adopted. The excited-atom density and spatial distribution are mapped by monitoring the absorption of a counterpropagating single-mode diode laser beam, tuned to Rb(5P_(J)-->7S_(1/2)) and Cs(6P_(3/2)-->8S_(1/2)) transitions respectively, which could be translated parallelly to the pump beams. The excited atom densities are combined with the measured fluorescence ratios to determine cross sections for the EP processes. It was found that Rb(5P_(J))+Cs(6P_(3/2)) collisions are more efficient than Rb(5P_(3/2))+Cs(6P_(3/2)) collisions for populating Cs(4F_(5/2)), while the opposite is true for populating Cs(4F_(7/2)).
Using two steps excitation of the cesium 8D atomic level in a cesium-potassium vapor mixture, we observed the reverse heteronuclear energy-pooling collision Cs(8D)+K(4S) →Cs(5D)+K(4P) at thermal energy. A double-modulation technique has been used to select the fluorescence contributions at the K(4PJ) exit channels due only to the above reactions. The ground state potassium atom density was measured by the absorption of line from a K hollow-cathode lamp. The measured density and fluorescence intensities have been used to obtain reverse energy-pooling rate coefficients. The contribution to the rate coefficients from other processes is discussed.