The cross sections of the excitation of cesium atoms by slow (E< or =5eV) electrons are calculated in the approximation of strong coupling of the 6s, 6p, and 5d states. It is shown that the inclusion of the 5d level reduces the total excitation cross sections significantly (by about 1/3). Such a change is explained by the presence of a long-range dipole interaction between the low-lying 6p and 5d levels. The influence of this interaction on the magnitude of the cross section is analyzed by a model example. (AIP)
The cross sections of the excitation of cesium atoms by slow (E< or =5eV) electrons are calculated in the approximation of strong coupling of the 6s, 6p, and 5d states. It is shown that the inclusion of the 5d level reduces the total excitation cross sections significantly (by about 1/3). Such a change is explained by the presence of a long-range dipole interaction between the low-lying 6p and 5d levels. The influence of this interaction on the magnitude of the cross section is analyzed by a model example. (AIP)
Cesium molecules are pumped by a CW dye laser. Some of the excited molecules then pre-dissociate or collisionally transfer excitation to produce excited atoms at the 5D and 6P levels. The cross sections (in units of 10-14cm2) for the excitation transfer process Cs(6P)+Cs(5D) →Cs(7DJ)+Cs(6S)for J being 5/2 and 3/2 are 5. 4 ± 50% and 4. 9 ± 50%, respectively. The cross sections (in units of 10-14cm2) for the excitation transfer out of the 7D doublet [i. e. , Cs(7DJ)+Cs(6S) →states other than Cs(7D)] for J being 5/2 and 3/2 are 1. 6 ±50% and 0. 34±50%, respectively. To obtain these cross sections, the intensities of 7D and 5D fluorescence emissions and the 6P atom density are measured by using the absorption equivalent width technique. The results are discussed in eomparison with those of other experiments.
Using selective stepwise excitation of the cesium 8S atomic level in Cs vapor, the collisional transfer and the population of the high-lying atomic states were studied in detail. At cesium densities of 10(16)-10(17) cm(-3), the rate coefficient of excitation collision [i. e., 8S+6S --> 6D+6S] was measured. Measurement of fluorescence intensities as a function of Cs density yields k6D = (2.4 +/- 0.5) x 10(-10) cm3 x s(-1). The 5D state was populated by the 8S --> 7P --> 5D transitions. The energy pooling collisions 5D+5D --> nL+6S (nL = 9D, 11S, 7F) were also studied. The rate coefficients were measured relative to the known rate coefficient of the collision [i. e. 6P+5D --> 6S+7D]. The densities of 6P state were combined with measured fluorescence ratios to determine rate coefficients for EP process. The average values (in unites of 10(-10) cm3 x s(-1)) for nL = 9D, 11S and 7F are 6.4 +/- 3.2, 1.0 +/- 0.5 and 8.4 +/- 4.2, respectively.
Using stepwise excitation of the cesium 8S atoms level in Cs vapor,several collisional and radiative processes have been identified from the intensities and spectra of the Cs fluorescence.The 5D state was populated by 8S→7P→5D transitions.In cesium densities 1016-1017?cm-3,the energy pooling collisions 5D+5D→nL+6S(nL=9D,11S,7F are studied.Since the 5D→6P(3.0-3.6 μm) fluorescence could not be detected with this experiment,the EP rate coefficients have been measured relative to the known rate coefficient of the collision,i.e.,6P+5D→6S+7D.The excited-atom density and spatial distribution were mapped by monitoring the absorption of a counterpropagating single-mode laser beam,tuned to 6P3/2→8S1/2 transition,which could be translated parallel to the pump beam.The excited atom densities are combined with measured fluorescene ratios to determine cross sections for the cesium energy pooling process.The average values(in units of 10-10?cm3s-1) for nL=9D,11S and 7F are 8.4±4.2,7.3±3.6,and 9.7±4.8,respectively.Influence on k11S and k7F of the energy transfer process 11S+6S7F+6S is also dicussed.
At a Cs density higher than 9 x 10(14) cm(-3), cesium vapor was irradiated in a glass fluorescence cell with pulses of radiation from an YAG-laser-pumped OPO laser, populating 6D(5/2) state by two-photon absorption. Energy transfer in Cs6(D(5/2)) + Cs (6S) collisions was studied using methods of atomic fluorescence. At the different Cs densities, we have measured the time-integrated intensities of the components and fitted a three-state rate equation model to obtain the cross sections. The experimental points were fitted to a straight line very well. The authors converted the gradient and intercept into cross sections. The cross section for 6D(5/2)-->6D(3/2) transfer is (2.1 +/- 0.4) x 10(14) cm2. The cross section for excitation transfer out of the 6D doublet is sigmaQ = (1.6 +/- 0.4) x 10(-14) cm2. The cross section on contains information on reverse energy pooling collisions [i.e., Cs(6D(3/2)) + Cs (6S(1/2))-->Cs(6P) + 6Cs(P)] and contribution from mining in 6Dj-->7P(J'), This latter contribution could be subtracted out using the results of a second experiment. At a Cs density lower than 6.0 x 10(12) cm3, the laser was used to pump the 6D(3/2) and 6D(5/2) states, respectively. The resulting fluorescence included the direct component emitted in the decay of the 6D(J) state and the sensitized component arising from the collisionally populated 7P(J') state. Relative intensities of the components yielded the cross sections. The cross-sections for the processes Cs(6D(5/2)) + Cs(6S(1/2))-->Cs(7P(J')) + Cs(6S(1/2)) are (1.6 +/- 0.5) x 10(-15) cm2. for J'= 3/2 and (6.5 +/- 2.1) x 10(-16) cm2, for J' = 1/2, respectively. The cross-sections for the processes Cs(6D(3/2) + Cs(6S(1/2))-->Cs (7P(J')) + Cs(6S(1/2)) are (1.9 +/- 0.6) x 10(-15) cm2. for J' = 3/2 and (7.6 + 2.4) x 10(-16) cm2, for J' = 1/2, respectively. The 6D(J) -->7P(J'), energy transfer rate coefficient is small. The total quenching rate coefficient out of the 6D(J) state is much larger. Evidence suggests that the quenching of the 6D(J) state is caused predominantly by reverse energy-pooling process. The cross section for this process, i.e., Cs(6D(3/2))+Cs(6S(1/2))-->Cs(6P) + Cs(6P) is (1.3 +/- 0.4) x 10(-14) cm2.
Applying the cw laser fluorescence method, the cross sections for the fine structure mixing and quenching of the Cs 6P state, induced by collisions with ground-state caesium atoms and molecules, have been measured. Caesium atoms were optically excited to the 5D J states via quadrupole-allowed 6S 1/2 5D J transitions, while the resonance states were populated by the radiative and collisional 5D J 6P J transitions. The relative populations of the Cs 6P J sublevels, as well as ratio of the 5D 3/2 to 6P 3/2 populations, were measured as a function of the caesium ground-state number density. From these measurements we obtained the cross section of (14±5) × 10 -16 cm 2 at T = 585 K for the process Cs(6P 1/2 ) Cs(6P 3/2 ) induced by collisions with ground-state caesium atoms. The applied experimental approach enabled the determination of the effective spontaneous rates for the 6P J states which are in agreement with the predictions of Holstein's theory. The cross sections for quenching of 6P J by caesium atoms and molecules were measured at T = 635 K and the obtained values are (1.6±1.4) × 10 -16 cm 2 and (1210±260) × 10 -16 cm 2 , respectively. Using recently calculated Cs*+Cs potentials we performed an analysis which shows a good agreement between the measured values and the theoretical estimates.
We report the results of a series of pulsed and cw laser experiments which measure spontaneous and effective lifetimes of the Cs(5DJ) levels and investigate excitation-transfer collisions involving Cs(5DJ) atoms and ground-state-cesium perturbers. With cw excitation of the dipole-forbidden but electric-quadrupole-allowed 6S1/2\ensuremath{\rightarrow}5D5/2 transition, we monitor the ratio of sensitized to direct fluorescence, i.e., I5D3/2\ensuremath{\rightarrow}6P1/2/I5D5/2\ensuremath{\rightarrow}6P3/2. A rate-equation analysis of these data yields values for the Cs(5D5/2)+Cs(6S)\ensuremath{\rightarrow}Cs(5D3/2)+Cs(6S) excitation-transfer rate, and for the rate of quenching of Cs(5D) by ground-state perturbers. The role of out-of-multiplet quenching is discussed at length, and we have demonstrated that quenching by ground-state atoms dominates over that by cesium dimers under these conditions. In the pulsed-laser experiments, the temporal evolution of the 5DJ\ensuremath{\rightarrow}6S and cascade 6PJ\ensuremath{'}\ensuremath{\rightarrow}6S fluorescence was observed following either direct forbidden-line pumping of one fine-structure level, or indirect excitation of both fine-structure levels (i.e., molecular excitation followed by predissociation). Analysis of the buildup and decay rates of the various levels as a function of cesium density yields values for the natural lifetimes of the Cs(5DJ) levels, as well as for the excitation transfer and quenching rates. Best values for the lifetimes and cross sections for Cs-Cs collisions obtained from these combined experiments are \ensuremath{\tau}5D=1250\ifmmode\pm\else\textpm\fi{}115 ns, \ensuremath{\sigma}5/2\ensuremath{\rightarrow}3/2=36\ifmmode\pm\else\textpm\fi{}8 \AA{}2, and \ensuremath{\sigma}5D=30\ifmmode\pm\else\textpm\fi{}3 \AA{}2. In addition, numbers for the 6P level-quenching cross sections due to collisions with Cs atoms and Cs2 molecules, respectively, were obtained: \ensuremath{\sigma}6P(Cs)=6.6\ifmmode\pm\else\textpm\fi{}3.0 \AA{}2 and \ensuremath{\sigma}6P(Cs2)=863\ifmmode\pm\else\textpm\fi{}260 \AA{}2. In the discussion, we show how these new values can be used to reconcile the seemingly discrepant results of several previous studies.