Excited Rubidium Research Articles

Centimeter-wave spectroscopy of highly excited rubidium atoms

One- and two-photon transitions between neighboring Rydberg states of rubidium with principal quantum numbers ranging from n = 50 to n = 63 have been studied. From these transition frequencies, corresponding to wavelengths in the centimeter domain, new values for quantum defects and fine- and hyperfine-structure splittings were obtained. The hyperfine structure of the 2S1/2 states was resolved up to n = 59. The data are compared with optically determined spectroscopic parameters, and fair agreement is found in most cases.

Collisions between excited potassium and rubidium atoms

The relaxation of highly excited Rb(72S12/) atoms by collisions with excited K(42P32/) atoms is investigated using the time-resolved spectroscopy technique. An estimation of the effective cross section is (5.6+or-0.6)*10-13 cm2 at a working temperature T=593K. A comparison is made with similar processes involving atoms of the same species.

Fine-structure-changing collision cross sections within the low-lyingnD2states of rubidium induced by ground-state rubidium atoms

The thermal cross sections for inelastic transfer of excited rubidium atoms from the $n^{2}D_{\frac{5}{2}}$ to the $n^{2}D_{\frac{3}{2}}$ fine-structure state caused by fine-structure-changing collisions with ground-state rubidium atoms have been measured by selective stepwise excitation of the rubidium atoms and observation of the resulting fluorescence. The cross sections (in units of ${10}^{\ensuremath{-}14}$ ${\mathrm{cm}}^{2}$) for $n$ being 5-9 are 2.9\ifmmode\pm\else\textpm\fi{}0.6, 6.9\ifmmode\pm\else\textpm\fi{}1.4, 11.5\ifmmode\pm\else\textpm\fi{}2.3, 17.1\ifmmode\pm\else\textpm\fi{}3.0, and 26.0\ifmmode\pm\else\textpm\fi{}5.0, respectively. The fine-structure-changing cross sections are of the order of the geometrical cross sections and increase slightly less than ${({n}^{*})}^{4}$ for the low-lying $n^{2}D$ states studied.

Inelastic collisions between selectively excited rubidium6D2-state atoms and noble-gas atoms: Fine-structure-state mixing

Inelastic collisional processes in fine-structure-state mixing have been studied by selective stepwise excitation and observation of the resulting fluorescence during collisions of excited rubidium 6/sup 2/D/sub 5/2/ state atoms with various noble-gas atoms. It is shown that for intermediately excited rubidium atoms the fine-structure-state mixing cross sections are generally p increasing from helium to xenon. The cross sections for the process Rb(6/sup 2/D/sub 5/2/)+A(n /sup 1/S/sub 0/)..-->..Rb(6/sup 2/D/sub 3/2/)+ A(n /sup 1/S/sub 0/)+..delta..E /sup 1/S/sub 0/)+..delta..E have the values sigma/sub fs/( = 2.4 +- 0.9, 3.1 +- 1.2, 2.6 +- 1.0, 5.8 +- 2.2, and 9.3 +- 5.6 in units of 10/sup -14/ cm/sup 2/, where A denotes in sequence any one of the noble gas atoms He, Ne, Ar, Kr, and Xe, respectively. Transfer cross sections for the transfer of excited Rb6 /sup 2/D-state atoms out of the doublet were also determined and are about an order of magnitude smaller than the fine-structure-mixing cross sections.

Penning and associative ionisation of highly excited rubidium atoms

Highly excited and resonant states are created in a rubidium vapour in order to study the collisional ionisation with the ground state and between these different excited species. A mass analysis allows one to separate the atomic and molecular channels. Penning ionisation with a resonant state is shown to have a great efficiency (rate coefficient greater than 10-8 cm3 s-1) for all the highly excited levels under study (6d, 8s, 7d). The associative ionisation rate coefficient between these excited atoms and a ground-state atom lies in the expected range 10-10 to 5*10-10 cm3 s-1 and seems to be independent of l j and values.

Inelastic collisions between selectively excited rubidium atoms and ground-state rubidium atoms

Inelastic-collision processes in fine-structure-changing collisions have been studied by selective stepwise excitation and observation of the resulting fluorescence. Hereby, the effect of ground-state rubidium atoms colliding with excited-state rubidium atoms was investigated. The ground-state density was changed by three orders of magnitude by performing the measurements over the temperature range of 75 to 200 /sup 0/C. The cross section for fine-structure-changing collisions (i.e., Rb(6/sup 2/D/sub 5/2/)+Rb(5/sup 2/S/sub 1/2/)..-->..Rb(6/sup 2/D/sub 3/2/) + Rb(5/sup 2/S/sub 1/2/)) is sigma/sub fs/ = (1.0 +- 0.6) x 10/sup -13/ cm/sup 2/. The cross sections for transfer out of the fine-structure doublet (i.e., Rb(6/sup 2/D)+Rb(5/sup 2/S/sub 1/2/)..-->.. states other than Rb(6/sup 2/D)) is sigma/sub tr/ = (3.8 +- 0.6) x 10/sup -13/ cm/sup 2/. It is demonstrated that for the intermediate excited rubidium states, both the fine-structure-changing and transfer cross sections are of the order of the geometrical cross section of the excited rubidium states.

Quenching collisions of rubidium in the nS (32⩽n⩽45) Rydberg levels with helium

Reports measurements of the cross sections for collisional quenching of highly excited rubidium nS (32<or=n<or=45) states by helium. A time-resolved selective field ionisation technique is used for this study. The experimental results are compared with the values calculated using an approximate scaling formula.

Collisional ionisation of highly excited rubidium S state

Collisional ionisation of the rubidium 9S state with other rubidium atoms is presented for the first time. The formation of atomic and molecular ions is analysed using a mass spectrometer. The associative ionisation cross section deduced from the experimental results (7.4*10-15 cm2) is in good agreement with the calculations of Janev. Some information on the possible mechanisms of production of the atomic ion Rb+ is also reported.

Collisionally induced ionization of Rubidium atoms in rydberg states

The efficiency of collisional ionization of excited rubidium atoms is demonstrated for Rb★—Kr collisions. Since the power required to optically saturate the Rydberg levels is much lower than for photoionization, the technique promises to reduce the laser requirements in single-atom detection and other resonance ionizatlon experiments.

Thermal collisions between highly excited and ground-state alkali atoms

Measurements have been made of the cross sections for collisional quenching of highly excited rubidium nS (12<or=n<or=18) and nD3/2(9<or=n<or=13) states by ground-state rubidium. The experimental values are shown to be close to the geometrical cross section. The large magnitude of the quenching cross section mainly reflects the long range of the Rydberg electron-alkali interaction.

Collisional properties of highly excited rubidium atoms

The quenching cross sections of various highly excited states of rubidium have been measured for different perturbing gases (He, Ar, Xe, ground-state rubidium). The quenching of the hydrogenic nF states is shown to be mainly a l-mixing process. The behaviour as a function of n (9<or=n<or=21) and the magnitude of the l-mixing cross sections seem mainly to reflect the range of interaction between the highly excited electron and the perturber.

Theory of fine structure transitions in excited rubidium atoms colliding with rare gas atoms

A theoretical model is presented for the interaction between an alkali atom in the first excited 2P state and a ground state rare gas atom, which is effective in causing transitions among the alkali fine structure states. The main difference from previously used models is a more detailed treatment of short range effects including deviations from straight line paths in the semiclassical treatment. An application to the case of Rb interacting with He, Ne, Ar, and Kr gives results for the depolarization and inelastic cross sections which are in reasonable accord with experiment.

Atomic and molecular fluorescence from laser excited diatomic cesium and rubidium

It has been found that several argon laser lines and the 6328 Å helium-neon laser line cause excitation of diatomic rubidium and cesium in the vapor phase to excited electronic states. The excitation of only a few, well separated rotation levels in the upper state, and the resulting simple line fluorescence spectra will allow determination of molecular constants not available by other methods. Atomic fluorescence was also present. Twenty-seven atomic cesium lines were observed between 3611 and 8946 Å under illumination at 4880 Å. The intensities of several atomic lines were found to have a quadratic dependence upon laser intensity, and are therefore attributed to excitation processes involving two photons.

The relationship between the fluorescence yield and the underpopulation of doublet excited states

The influence of radiative non-equilibrium on the occupation of excited metal states in flames can be investigated by measuring the deviation Δ T of line reversal (or excitation) temperature T L from “true” (or translation) temperature T t of the flame as a function of metal concentration. In this paper it is shown that, under certain conditions concerning the rates of the de-excitation processes, the measurements of Δ T for atoms with close lying upper levels (such as the alkali atoms) may be interpreted by assuming a single excitation level. In that case, the fluorescence yield Y D , obtained when both lines are used in excitation and measured in fluorescence, occurs as a parameter in the expressions which describe the behavior of Δ T for low and high metal densities. The theoretical relationships were checked by comparing the experimental values of Y D and Δ T for the yellow sodium doublet in a typical hydrogen-oxygen-argon flame. Satisfactory agreement was found. In order to determine more reliably the low density asymptote of the excitation temperature, the variation of Δ T with atomic density was theoretically analysed to first order in the density. Fluorescence yield factors were again measured for several alkali lines with an improved experimental set-up and agreed with our previous results, (1,2,3) except for the sodium doublet. The effective cross sections (see Table 1) derived from these yield factors for the quenching of excited sodium (3P 1 2 , 3 2 ) , potassium (4P 1 2 , 3 2 ) and rubidium (5P 1 2 , 3 2 ) atoms by various flame molecules, are in satisfactory agreement with the results of Jenkins' flame experiments. (4,5)

Sensitized fluorescence in vapors of alkali metals. XI Energy transfer in potassium–rubidium collisions

Sensitized fluorescence in rubidium vapor, induced by collisions with excited potassium atoms, was investigated to determine the total cross sections for inelastic collisions between excited potassium atoms and rubidium atoms in their ground states. The collision cross sections for the various excitation transfer processes are as follows: Q12′ (K42P1/2 → Rb52P3/2) = 40 Å2, Q22′ (K42P3/2 → Rb52P3/2) = 27 Å2, Q11′ (K42P1/2 → Rb52P1/2) = 2.7 Å2, and Q21′ (K42P3/2 → Rb52P1/2) = 1.9 Å2. The partial pressure of potassium vapor in the K–Rb mixture was kept largely below 10−5 mm Hg to eliminate effects due to the trapping of potassium resonance radiation.

Sensitized fluorescence in vapors of alkali metals. XII. 42P1/2–42P3/2 mixing in potassium, induced in collisions with ground-state rubidium atoms

The total cross sections for collisions between excited potassium and unexcited rubidium atoms, leading to the transfer of excitation between the 42P states in potassium, have been determined in a sensitized fluorescence experiment. The experiments were carried out at partial pressures of potassium vapor lower than 10−5 mm Hg, at which the imprisonment of resonance radiation may be disregarded. The cross sections Q12″ (42P1/2 → 42P3/2) and Q21″ (42P1/2 ← 42P3/2) equal 260 Å2 and 175 Å2, respectively, and are in the ratio predicted by the principle of detailed balancing.

Quenching of excited rubidium (5 2P) atoms in flames

An alternating current photoelectric device (compare the work of Boers, (1) Hooymayers et al (2-4) and Hooymayers (5)) has been used for determining the yield factor p of resonance fluorescence for the infrared rubidium doublet (7800/7947 Å). From the p-values measured in five different hydrogen flames at about 2000°K and 1 atm pressure, the specific effective quenching cross-sections (2-5) S of the excited Rb atoms in collision with some molecules could be derived. The cross section values for these molecules were found to be S H 2 = 3·6(±0·4) Å 2, S N 2 = 25(±1·5) Å 2, S O 2 = 83(±5) Å 2 and S H 2 O = 4·0(±0·8) Å 2 respectively. In the derivation of the S-values it was assumed that S Ar is negligibly small. The S-values for the diatomic molecules may be considered as valid for a temperature of about 1900°K, whole S H 2O is valid at about 2100°K. The possibility of a resonance effect between the excited Rb-level and the molecular vibrational levels is discussed.

SENSITIZED FLUORESCENCE IN VAPORS OF ALKALI METALS: VII. ENERGY TRANSFER IN RUBIDIUM–CESIUM COLLISIONS

Sensitized fluorescence in cesium vapor induced by collisions with excited rubidium atoms was investigated in order to determine the total cross sections for inelastic collisions between excited rubidium atoms and cesium atoms in their ground states. The partial pressure of the rubidium vapor in the Rb–Cs mixture was kept below 2 × 10−5 mm Hg in order to eliminate effects due to the trapping of the Rb resonance radiation. The collision cross sections for the various excitation transfer processes are as follows: Q12′(Rb 5 2P1/2 → Cs 6 2P3/2) = 1.5 Å2; Q11′(Rb 5 2P1/2 → Cs 6 2P1/2) = 0.5 Å2; Q22′(Rb 5 2P3/2 → Cs 6 2P3/2) = 0.9 Å2; Q21′(Rb 5 2P3/2 → Cs 6 2P1/2) = 0.3 Å2. The fact that the cross sections are considerably smaller than those for collisions between similar atoms indicates that the Rb–Cs interactions probably involve van der Waals' forces with a much shorter range than exchange forces, which play a dominant role in Rb–Rb or Cs–Cs collisions.