The Rb(5D,7S)+H2→RbH+H photochemical reaction has been studied.The RbH molecules are formed in three-body reactive collisions between exited 5D or 7S atoms and ground state H2 molecules.Using two-photon absorption.Rb vapor mixed with Hz gas was irradiated in a glass fluorescence cell with pulses of 778.2nm or 760.1nm radiation from a YAG laser pumped OPO laser,populating one of the 5D and 7S states by two-photon absorption.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.The measured fluorescent intensities are proportional to the products of the appropriate population.The rate equations were solved.We estimated the value of cross sections for collisional energy transfer from Rb(5D) to Rb(7S), from Rb(7S)to Rb(5D) to be (6.9±1.4)×10-17 and(2.1±0.4)×10-16 cm2,respectively.The cross sections for reactive collisions Rb(5D)+H2RbH+H and Rb(7S)+H2→RbH+H are (4.3±1.1)×10-17 and(5.8±1.5)×10-17 cm2,respectively.The relative reactivity with H2 for two studied atoms is in an order of Rb(7S)Rb(5D).
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).
The Rb(5DJ )+H2 → RbH+H photochemical reaction has been studied.Rb vapor mixed with H2 is irradiated in a glass cell with 778-nm pulses which populate one of the 5 2 D states by two-photon absorption.Measurements for the relative intensities of the atomic fluorescence and the absorption of the RbH product near the axis of the cell yield the rate coefficients for the Rb(5D 3/2 )+H2 and Rb(5D 5/2 )+H2 reactions, which are (3.6 ± 1.3) × 10 -11 and (1.7 ± 0.6) × 10 -11 cm 3 /s, respectively.The relative reactivity with H2 for Rb(5D 3/2 ) is higher than that for Rb(5D 5/2 ).
Rb vapor was irradiated in a glass fluorescence cell with pulses of radiation from a YAG laserpumped OPO laser,populating 5D_j(or 7S) state by two-photon absorption.Energy transfer in Rb (5D_J,7S)+Rb(5S) collision is studied using methods of atomic fluorescence.The resulting fluorescence includes a direct component emitted in the optically excited state decay and a sensitized component arsing. from the collisional populated state.At the different densities of the components,fitting a three-state rate equation model,the cross sectionσ=(3.7±0.9)×10~(-14) cm~2 was obtained for Rb(5D_(5/2))→Rb(5D_(3/2)) transfer.The cross section for excitation transfer out of the 5D_J doublet are(3.1±1.2)×10~(-14) cm~2(for J = 5/2) and(2.0±0.6)×10~(-14) cm~2(for J = 3/2),respectively.The energy transfer cross section for the Rb(5D)→Rb(7S) is small,(1.6±0.4)×10~(-16) cm~2.The 5D_J state is quenched mainly in the reverse energy pooling processes,i.e.Rb(5D_J)+Rb(5S)→Rb(5P)+ Rb(5P).
The radiation of a laser photoexcited Rb atoms from the ground state to the 5P3/2 level in a mixture of Rb vapor and hydrogen. The energy-pooling collision 5P3/2 + 5P3/2 --> 5S1/2 + 5D producted 5D state. The Rb (5P3/2) density and spatial distribution were mapped by monitoring the absorption of a counter-propagating laser beam, tuned to the 5P3/2 --> 7S1/2 transition, which could be translated parallel to the pump beam. In the presence of radiation trapping, the spontaneous radiation rate is multiplied by the transmission factor T5P3/2 --> 5S1/2, which describes the average probability that photons emitted within the fluorescence detection region can pass through the optically thick vapor without being absorbed. The T5P3/2 --> 5S1/2 is related to the frequency dependent absorption cross section and the density and spatial distribution of atoms in the level of the transition. The effective radiative rates of the Rb D2 line as a function of the H2 pressure were obtained. These quantities were combined with the measured excited atom density and fluorescence ratio to yield absolute energy-pooling rate coefficient. The quenching collision Rb (5P3/2) + H2 (v = 0) --> Rb(5S) + H2 (v = 2) producted state H2 (v= 2). This process is at least 16 times faster than the Rb (5P3/2) radiative decay rate. The reverse process of this process is relatively unlikely due to their large translational energy defect. The cross section for the process H2 (v = 2) + H2 (v = 0) --> H2 (vn = 1) + H2 (v = 0) + 3 920.2 cm(-1) is 7.7 x 10(-19) cm2. Hence the relaxation rate of this vibrational level is relatively slow and the nuclear spin statistics is conserved. The H2 (v = 2) density was determined by using the cross section for Rb (5P3/2)-H2 quenching. RbH was fromed by the Rb(5D) + H2 and Rb (5P3/2) + H2 (v = 2) reactions and observed by laser absorption. The ratio of 5D --> 5P3/2 to 5P3/2 --> 5S1/2 fluorescence was measured as a function of the H2 density. The absorption of the laser beam tuned to the X1sigma+ --> A1sigma+ line of RbH was also measured as a function of the H2 density. From these measurements we obtained the cross section of 4.02 x 10(-7) cm2 for the process Rb (5D) + H2 --> RbH + H. The cross section for Rb (5P3/2) + H2 (upsilon = 2) --> RbH + H is 1.00 x 10(-8) cm2. This experiment showed that under our experimental conditions, RbH molecules are not created by a direct interaction of Rb(5P) with H2 but through a two-step reaction.
Cross sections for $7^{2}D_{\frac{3}{2}}\ensuremath{\leftrightarrow}7^{2}D_{\frac{5}{2}}$ transfer in Rb, induced in collisions with He, Ne, Ar, and with ground-state Rb atoms, have been determined using methods of atomic fluorescence. Rb vapor, pure or mixed with a noble gas, was irradiated in a glass fluorescence cell with pulses of 660-nm radiation from a
N2-laser-pumped dye laser, populating one of the
2D states by two-photon absorption. 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. Relative intensities of the components yielded the cross sections for
72D mixing: $Q(^{2}D_{\frac{3}{2}}\ensuremath{\rightarrow}^{2}D_{\frac{5}{2}})=8.8,6.5,10.4, \mathrm{and} 30$; $Q(^{2}D_{\frac{3}{2}}\ensuremath{\leftarrow}^{2}D_{\frac{5}{2}})=5.8,4.0,6.9, \mathrm{and} 18$, in units of ${10}^{\ensuremath{-}14}$
cm2 for He, Ne, Ar, and Rb, respectively. Cross sections for the effective quenching of the
2D states were also determined.
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).