Cs vapor was created in a resistively heated,cross-shaped stainless-steel heat-pipe oven with quartz windows.H2 gas filled in the cell for use both as a buffer gas and as a reaction partner.Cs atoms were excited to 6D3/2 state by two-photon absorption.The 7P1/2 and 7P3/2 were populated by the radiative and collisional 6DJ→7PJ′ transition.The cross sections for 6DJ7PJ′ transfer induced by collision with H2 molecules have been determined using methods of atomic fluorescence.The resulting fluorescence included a direct component emitted in the decay of the optically excited state and sensitive component arising from collisionally populated states.The time-integrated fluorescence intensities for atomic transitions 6D5/2→6P3/2,6D3/2→6P3/2,7P3/2→6S1/2 and 7P1/2→6S1/2 were measured at the defferent H2 densities.The relative time-integrated population densities were obtained as a function of H2 densities.By the set of the rate equations,the cross-sections have been determined to be σ6D3/27P3/2=(3.1±0.8)×10-16cm2,σ6D3/27P1/2=(1.7±0.4)×10-16cm2,σ6D5/27P3/2=(1.5±0.4)×10-16cm2 and σ6D5/27P1/2=(1.3±0.3)×10-16 cm2.The cross sections for quenching of 7PJ′ by H2 are(2.5±0.6)×10-16 cm2(for 7P3/2) and(4.0±1.0)×10-16 cm2(for 7P1/2).Evidence suggests that the substantial fraction of quenching cross section is reactive.The relative reactivity with H2 is an order 7P1/27P3/2.
Cs vapor was created in a resistively heated,cross-shaped stainless-steel heat-pipe oven with quartz windows.H2 gas filled in the cell for use both as a buffer gas and as a reaction partner.Cs atoms were excited to 6D3/2 state by two-photon absorption.The 7P1/2 and 7P3/2 were populated by the radiative and collisional 6DJ→7PJ′ transition.The cross sections for 6DJ7PJ′ transfer induced by collision with H2 molecules have been determined using methods of atomic fluorescence.The resulting fluorescence included a direct component emitted in the decay of the optically excited state and sensitive component arising from collisionally populated states.The time-integrated fluorescence intensities for atomic transitions 6D5/2→6P3/2,6D3/2→6P3/2,7P3/2→6S1/2 and 7P1/2→6S1/2 were measured at the defferent H2 densities.The relative time-integrated population densities were obtained as a function of H2 densities.By the set of the rate equations,the cross-sections have been determined to be σ6D3/27P3/2=(3.1±0.8)×10-16cm2,σ6D3/27P1/2=(1.7±0.4)×10-16cm2,σ6D5/27P3/2=(1.5±0.4)×10-16cm2 and σ6D5/27P1/2=(1.3±0.3)×10-16 cm2.The cross sections for quenching of 7PJ′ by H2 are(2.5±0.6)×10-16 cm2(for 7P3/2) and(4.0±1.0)×10-16 cm2(for 7P1/2).Evidence suggests that the substantial fraction of quenching cross section is reactive.The relative reactivity with H2 is an order 7P1/27P3/2.
Cs vapor, mixed with a gas was irradiated in a glass fluorescence cell with pulses of 886nm radiation from a YAG-laser-pumped OPO laser, populating 6D3/2 state by two-photon absorption. Cross sections for 6D3/2 --> 6D5/2 transition induced by collisions with various H(e) atoms and H2 molecules were determined using methods of atomic fluorescence. The resulting fluorescence included a direct component emitted in the decay of the optically excited state and a sensitized component arising from the collisionally populated state. At the different densities, we have measured the relative time-integrated intensities of the components and fitted a three-state rate equation model to obtain the cross sections for 6D3/2 --> 6D5/2 transfer: sigma = (55 +/- 13) x 10(-16) and (16 +/- 4) x 10(-16) cm2 for H2 and H(e), respectively. The cross sections for the effective quenching of the 6D5/2 state were also determined. The total transfer rate coefficients from the 6D5/2 state for H(e) is small [1.2 x 10(-10) cm3 x s(-1)]. The total quenching rate coefficient of the 6D5/2 state is larger for H2 [6.7 x 10(-10) cm3 z s(-1)]. For H2 case, the quenching rate coefficient corresponds to reaction and nonreactive energy transfer. Evidence suggests that the nonreactive energy transfer rate coefficient is [6.3 x 10(-10) cm3 x s(-1)]. Hence the authors estimated the cross section (2.0 +/- 0.8) x 10(-16) cm2 for reactive process Cs(6D5/2) + H2 --> CsH + H. Using the dependence on the pressure of H2 (or H(e)) of the integrated fluorescence monitored at the 6D5/2 --> 6P3/2 transition the cross section (4.0 +/- 1.6) x 10(-16) cm2 for Cs (6D3/2) + H2 --> CsH + H was obtained. Thus, the relative reactivity with H2 follows an order of Cs (6D3/2) > Cs (6D5/2).
Cs vapor in a glass cell was irradiated with pulses of radiation from a YAG-laser-pumped OPO laser,populating 7DJ state by two-photon absorption.Energy transfer in 7DJ+6S1/2 collision is studied using methods of atomic fluorescence.The resulting fluorescence included a direct component arising from the decay of the optically excited and a sensitized component arising from the collisionally populated state.At the different densities,we have measured the time-integrated intensities of the components and fitted a three-state rate equation model to obtain the cross section σ=(2.9±0.7)×10-14cm2 for 7D5/2→7D3/2 transfer.The cross section for excitation transfer out of the 7DJ doublet are(7.4±2.1)×10-14 cm2(for J=5/2) and(6.6±1.8)×10-14 cm2(for J=3/2),respectively.A comparison with previous results yields that the cross sections for 7DJ→8P transfer are(0.6±0.3)×10-14 cm2(for J=5/2)and(0.8±0.4)×10-14 cm2(for J=3/2),respectively.The 7DJ state is quenched mainly in the reverse energy polling processes(i.e.,7DJ+6S→5D+ 6P).
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.
By applying the laser absorption and fluorescence method,the cross sections for the fine structure mixing and quenching of the Cs(6P) state,induced by collision with He atoms,have been measured.Cesium atoms were optically excited to the 6P3/2 state.The excited atom density and spatial distribution were mapped by monitoring the absorption of a counterpropagating single mode laser beam,which was tuned to the 6PJ→8S1/2 transitions.The effective radiative rates were calculated for the 6PJ→6S transitions.The fluorescence intensity I895 of the sensitized 6P1/2→6S1/2 emission was measured as a function of He density in the range 0.5×1018～4×1018cm-3 at constant temperature T=337 K.It was found that the quantity N/I895 exhibited a parabolic dependence on N,confirming that the quenching of the 6PJ states was due to collision with He atoms,not ground state Cs atoms.The coefficients of the second-order polynomial fitted through the measured data yielded the cross sections σ3/2→1/2=(1.46±0.51)×10-19 cm2 and σD=(2.28±0.80)×10-18 cm2 for the 6PJ fine structure mixing and quenching,respectively,due to collision with He atoms.
Rb vapor, mixed with H2 or He, was irradiated in a glass fluorescence cell with pulses of radiation from a YAG-laser-pumped OPO laser, populating 5D or 7S state by two-photon absorption. The temperature dependence of the cross sections for 5D-7S transfer induced by collisions with He atoms and H2 molecules was determined using methods of atomic fluorescence. The resulting fluorescence included a direct component emitted in the decay of the optically excited state and a sensitized component arising from the collisionally populated state. At the different densities, the authors have measured the relative time-integrated intensities of the components and fitted a three-state rate equation model to obtain the reactive and nonreactive cross sections for Rb(7S-5D)-H2, He collisions. The cross sections of transfer for Rb(7S)+H2-->Rb(5D)+H2 decrease with increasing T. The cross sections for 5D-->7S increase with increasing T. At the different temperatures, the cross sections of transfer for (7S-5D)-He collisions coincide with the principle of detailed balance. The total transfer rate coefficients out of the 7S or 5D state for He were small. The total quenching rate coefficient out of the 7S or 5D state was much larger for H2. In the case of H2, the quenching rate coefficient corresponds to reaction and nonreactive energy transfer. In reaction of Rb(7S, 5D)+H2-->RbH+H, the ratio between the reactive cross sections was found to be sigma(-)[Rb(7S)+H2]/sigma(-)(Rb(5D)+H2]=1.5. The relative reactivity with H2 was in an order of Rb(7S)>Rb(5D).
Applying the CW laser absorption and fluorescence method, the cross sections for the fine structure mixing and quenching of the Cs(6P) state, induced by collision with N2 molecules, were measured. Cesium atoms were optically excited to the 6P3/2 state. The excited atom density and spatial distribution were mapped by monitoring the absorption of a counterpropagating single mode laser beam, tuned to the 6P1 --> 8S(1/2) transitions, which could be translated parallel to the pump beam. The 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 6P --> 6S(1/2) transitions. The N2 caused line broadening and therefore increased the effective pumping rate and radiative rates. The effective radiative rates were calculated for the 6P(J) --> 6S transitions. The fluorescence intensity I895 of the sensitized 6P(1/2) --> 6S(1/2) emission was measured as a function of N2 density in the range 2 x 10(16) < N < 1.4 x 10(17) cm(-3) at a constant temperature T = 337 K, which produced cesium density N0 = 1.25 x 10(12) cm(-3). The transparency of the cell was obtained by the absorption of light beam passing the cell. The transparency is not a simple function of N2 density. It was found that the quantity N/I895 (I895 being corrected for the cell transparency) exhibited a parabolic dependence on N, confirming that the quenching of the 6P(J) states is due to collision with N2 molecules instead of Cs ground state atoms. The coefficients of the second-order polynomial fitted through the measured data yielded the cross sections sigma3/2 --> 1/2 = (0.42 +/- 0.17) x 10(-16) cm2 and sigmaD = (1.31 +/- 0.52) x 10(-16) cm2 for the 6P(J) fine-structure mixing and quenching, respectively, due to collision with N2 molecules. The quenching rate coefficient is about 3 times larger than the rate coefficient for the fine-structure mixing. Our values for these cross sections are in agreement, within combined error bars, with the values we have recently obtained under different experimental conditions.