Diffusion of barium atoms in the 6s5d triplet-D(J) levels and the 6s(2) singlet-S(0) ground state through noble gas perturbers

E. Ehrlacher

R. K. Namiotka, E. Ehrlacher, J. Sagle +5 more

We describe a set of experiments that investigate diffusion of barium 6s5d${\mathrm{}}^{3}$${\mathit{D}}_{\mathit{J}}$ metastable level and 6${\mathit{s}}^{2}$${\mathrm{}}^{1}$${\mathit{S}}_{0}$ ground-state atoms through the noble gases: He, Ne, Ar, Kr, and Xe. The barium metastable levels were populated through optical pumping of the 6${\mathit{s}}^{2}$${\mathrm{}}^{1}$${\mathit{S}}_{0}$\ensuremath{\rightarrow}6s6p${\mathrm{}}^{3}$${\mathit{P}}_{1}^{\mathit{o}}$ intercombination transition with a pulsed laser, followed by spontaneous or stimulated emission into the 6s5d${\mathrm{}}^{3}$${\mathit{D}}_{1,2}$ levels. Collisional mixing then distributed population throughout the 6s5d${\mathrm{}}^{3}$${\mathit{D}}_{\mathit{J}}$ levels. A weak narrow-band cw laser was tuned to appropriate transitions to probe the spatial distribution of metastable level atoms, as well as the hole created in the ground-state spatial distribution, by the pulsed laser. Time-dependent absorption coefficients were obtained by measuring the transmission of the probe laser at several different pump-probe spatial separations. From these absorption data, spatial number density profiles were mapped out for various times following the firing of the pump laser. These density profiles were used to determine the diffusion coefficient for each state at a particular buffer-gas pressure and temperature. From these pressure- and temperature-dependent diffusion coefficients D, we determined the thermally averaged diffusion cross sections ${\mathrm{\ensuremath{\sigma}}}_{\mathit{D}}$(6s5d${\mathrm{}}^{3}$${\mathit{D}}_{\mathit{J}}$) and ${\mathrm{\ensuremath{\sigma}}}_{\mathit{D}}$(6${\mathit{s}}^{2}$${\mathrm{}}^{1}$${\mathit{S}}_{0}$) for the metastable and ground-state atoms diffusing through the noble gases, respectively. We also report values for the scaled standard diffusion coefficients ${\mathit{D}}_{0}$. Our experimental values of the thermally averaged diffusion cross sections ${\mathrm{\ensuremath{\sigma}}}_{\mathit{D}}$(6s5d${\mathrm{}}^{3}$${\mathit{D}}_{\mathit{J}}$) and ${\mathrm{\ensuremath{\sigma}}}_{\mathit{D}}$(6${\mathit{s}}^{2}$${\mathrm{}}^{1}$${\mathit{S}}_{0}$) for the barium-helium system are compared with values calculated from published, theoretical barium-helium potentials and the agreement is excellent. \textcopyright{} 1996 The American Physical Society.

Jacques Boulmer, Pierre Camus, Jean-Marie Lecomte +1 more

J. Brust, Alan C. Gallagher

We present a time resolved study of excitation transfer processes between the low lying excited states of barium (6s6p $^{3}$${\mathit{P}}_{\mathit{J}}$, 6s5d $^{1}$${\mathit{D}}_{2}$, 6s5d $^{3}$${\mathit{D}}_{\mathit{J}}$) induced by collisions with noble gases. The transient excited state populations have been measured by means of fluorescence and absorption spectroscopy. Cross sections for spin-changing collisions from $^{3}$${\mathit{P}}_{1}$ to $^{1}$${\mathit{D}}_{2}$ and from $^{1}$${\mathit{D}}_{2}$ to $^{3}$${\mathit{D}}_{3}$ as well as for fine-structure mixing within the $^{3}$D multiplet were obtained by fitting the numerical solution of a seven-state system of rate equations including diffusion to the experimental data. We compare our results to experimental findings for other alkaline earth metals and report an improved value of the lifetime of the 6s6p $^{3}$${\mathit{P}}_{1}$ state of barium.

Leszek Sirko, K. Rosiński

The impact broadening of Na(nP1/2) (n=6-24), K(nP1/2) (n=8-24) and Rb(nP12/) (n=10-24) levels by noble-gas atoms, N2 molecules and alkali atoms in the ground state has been investigated. Broadening cross sections have been evaluated on the grounds of contributions coming from Rydberg-electron-perturber and ionic core-perturber scattering. Broadening cross sections for Cs(nD3/2)+Cs(6S) collisions for n=11-23 have also been calculated to compare with the experimental ones. Theoretically evaluated broadening cross sections for K(nP12/)+K(4S) and Cs(nD3/2)+Cs(6S) collisions appeared to be in good agreement with existing experimental data.

Wolfgang Sandner, Kambiz Ali Safinya, F. Gounand +1 more