The NaK 1 3 ⌬ state has been studied by the perturbation-facilitated optical-optical double resonance technique. Mixed singlet-triplet levels, A(2) 1 ⌺ ϩ (v A ,J)ϳb(1) 3 ⌸(v b ,J), were pumped from thermally populated rovibrational levels of the ground state, X(1) 1 ⌺ ϩ (v X ,JϮ1), using a single-mode cw dye laser. A single-mode cw Ti:Sapphire laser was then used to further excite the NaK molecules to various 1 3 ⌬(v ⌬ ,N ⌬ ,J ⌬ ) rovibrational levels which were detected by observing collision-induced 3 ⌳→a(1) 3 ⌺ ϩ fluorescence in the green part of the spectrum. The measured energies of the 1 3 ⌬(v ⌬ ,N ⌬ ) levels were fit to a Dunham expansion, and the Dunham coefficients were used to construct the RKR potential curve. Absolute numbering of the 1 3 ⌬ state vibrational levels was established by a comparison of experimental and calculated 1 3 ⌬(v ⌬ ,N ⌬ ,J ⌬ ) ←b(1) 3 ⌸(v b ,J b ) absorption line strengths. A deperturbation program was used to determine the vibration-dependent 1 3 ⌬ state spin-orbit interaction parameter. Hyperfine structure of the 1 3 ⌬ state was studied, and the Fermi-contact interaction term for this state was determined to be ϳ0.0111 cm Ϫ1 .
A two-step excitation experiment has been employed to measure the collisional rate coefficients and to study the velocity distribution of Cs͑6P 1/2 ͒ atoms that have undergone a single hyperfine state-changing collision with Ar. In addition, argon pressure broadening rates and shifts of the cesium 6P 1/2 ͑FЈ͒ → 8S 1/2 ͑FЉ͒ transitions have been determined. In the experiment, a single mode, cw Ti:sapphire laser is tuned to line center of the 6S 1/2 ͑F =4͒ → 6P 1/2 ͑FЈ = 3 or 4͒ transition. Then, the frequency of a single mode cw dye laser is scanned over the 6P 1/2 → 8S 1/2 manifold to probe the populations of the 6P 1/2 hyperfine levels. Absorption of probe laser photons is monitored by detecting 8S 1/2 → 6P 3/2 fluorescence. The experiment is conducted at room temperature, where the Cs density is low ͑n ϳ 3.4ϫ 10 10 atoms cm −3 ͒, and thus the probability of a Cs-Cs collision is negligible during the Cs͑6P 1/2 ͒ radiative lifetime. The Ar pressure is varied from 0 to 1.52 Torr, and Cs-Ar collisions cause population to be transferred from the directly excited 6P 1/2 ͑FЈ͒ level to the other 6P 1/2 hyperfine level. The data are analyzed using a density matrix formalism to yield the rate coefficients for Cs͑6P 1/2 ͒-Ar hyperfine state-changing collisions. In addition, the one-dimensional velocity changing collision kernel for Cs͑6P 1/2 ͒ atoms prepared with v z = 0 that undergo FЈ =3↔ FЈ = 4 hyperfine state-changing collisions with argon is reported.
Alkali atoms that are diffusing away from a source via multiple surface scattering
in a nonstick coated glass tube are monitored by laser fluorescence. Densities
are measured by fluorescence intensity and weak-field absorption, and
small asymmetries in the line shape provide a measurement of the flux.
Average velocities as small as 0.3% of the thermal velocity can be resolved
using the technique presented. Model calculations are presented and fit
to the data, providing approximate values for the sticking probability,
and the probability of specular scattering versus diffuse scattering
(related to momentum accommodation). For the silane-based coating
SurfaSilTM,
we find that the scattering is mostly diffuse, and that the sticking probability is of
the order of 10−4 or 10−3. With refinement, the technique can be used to measure
the variation in the sticking probability along the length of the tube, which could
be useful for studying and improving gas separation columns. We present
numerical calculations of surface light-induced drift (SLID) effects, but no
evidence for SLID is observed experimentally.
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