Atomic Reservoir Research Articles

Collisional energy transfer in gaseous xenon with vacuum ultraviolet laser excitation of the 5d[1/2]1 atomic level

Time-resolved analysis of the luminescence decay of gaseous xenon has been carried out with one-photon excitation of the 5d[1/2]1 atomic level for the first time. The one-photon selective excitation is realized with a coherent vacuum ultraviolet (VUV) light source generated via nonlinear processes in mercury vapor. Dominant three-body recombination of Xe(5d[1/2]1) atoms with a rate constant of 3.2(0.3)×10−31 cm6 s−1 has been found. Resonance radiation from this atomic level undergoes a self-trapping, which results in its dominant fluorescence decay in the IR with t=4.9(0.7) μs. Branching into two relaxation channels is found at low xenon pressure (5–100 mbar)—both avoiding the 6s[3/2]1 first resonance atomic level and terminating by VUV emission. At higher pressure, the relaxation kinetics changes displaying after 500 mbar the well known effect of ‘‘atomic reservoir’’ and radiation from the A1u/0−u molecular state with lifetime of 101(4) ns. The scheme of energy relaxation involving the 5d[1/2]1 atomic level is discussed.

Analysis by the recursion method of the electronic transfers involved in the dihydrogen chemisorption on a platinum cluster

As a first example of a possible analysis of elementary steps of a heterogeneous catalytic reaction, the electronic transfers and the associated energy costs involved in the dihydrogen adsorption on various sites of a Pt 13 cluster have been analysed in terms of the changes occurring in the local densities of states computed by the recursion method. The Hamiltonian defining the various metal-metal, hydrogen-hydrogen, and metal-hydrogen interactions is of extendedHückel-type. This method gives local information on the behaviour of the surface orbitals along the reaction path. In particular, it shows the role of a late electron transfer from d-type to s or p-type metal orbitals, and it exhibits the role of electronic reservoir of the platinum atoms not directly bound to the adsorbate, in the electron transfer. Furthermore, it shows that the height of the activation barrier and the energy difference of the whole process are mainly related to the energy positions of the local HOMO and LUMO contributions of the metal atoms in direct interaction.

Periodic Fluctuations in a Fabry-Perot Cavity in Resonance with a Reservoir of Two-level Atoms

The Maxwell equations for the field in a cavity are modified to include the effect of irradiation by a reservoir of two-level atoms. A canonical treatment of the time-dependent field modes leads to predictions of the changes in the electric and magnetic field intensities, and in the photon statistics, for sufficiently small times. Coherent states evolve to squeezed states. The frequency converter and possible resonance phenomena are discussed.

Field Fluctuations in a Fabry-Pérot Cavity in Resonance with a Reservoir of Two-level Atoms: I. Adiabatic fluctuations

A canonical approach using variable mass parameters presented in an earlier paper is applied to the case of an electromagnetic field of slowly varying intensity in a cavity in the presence of a reservoir of resonant two-level atoms. The effect is to replace any cavity frequency y s by a reduced variable frequency z s (t). Calculations have been carried out for the changes in the atomic transition amplitudes that are produced by an externally imposed adiabatic change in the field intensity, or by a small low-frequency periodic fluctuation in the photon population which could be due to the Rabi flopping of the atoms.

Field Fluctuations in a Fabry-Pérot Cavity in Resonance with a Reservoir of Two-level Atoms: II . Non–adiabatic periodic fluctuations

Two kinds of periodic fluctuation in the intensity of the field in a Fabry-Pérot cavity are considered: (a) a strong pulsation with periodically vanishing intensity, identifiable with the interaction of a low-density atomic reservoir and (b) a pulsation of adjustable strength and non-vanishing intensity whose frequency is approximately twice that of a natural mode. Self-consistent values are found in each case for the resonance frequency and for the on-resonance Rabi frequency. Case (b) may be identified with a pump-signal-idler system in which the signal and idler frequencies are approximately equal, and these modes can be damped out if the pulsation is sufficiently strong.

Field Fluctuations in a Fabry-Pérot Cavity in Resonance with a Reservoir of Two-level Atoms

Field Fluctuations in a Fabry-Pérot Cavity in Resonance with a Reservoir of Two-level Atoms

Why not ICP as atom reservoir for AAS?

The sensitivity S A of determination by inductively coupled plasma atomic absorption spectrometry (ICP—AAS) is discussed. All important factors influencing S A are comprised in one single sensitivity formula, which allows an estimate to be made of the correct order of magnitude of S A for both flame—AAS and ICP—AAS measurements. The most important analytical factors are the degree of dissociation and ionization (0≤ f C , and f I ≤1), the dilution factor f D , which takes into account the dilution of the analysis element A by its transition from the solution to the ICP, and the absorption path length b. Like flame—AAS, an analytical approach using ICP—AAS has high selectivity and makes it possible to carry out determinations without chemical and ionization interferences. This important advantage of ICP—AAS in comparison to flame—AAS is based on the fact that the ideal condition f C →1 and Δ f→0 for the analysis and standard solutions can be much more easily realized in the ICP than in flames. Serious disadvantages of an ICP as an atomic reservoir for AAS are the reduced sensitivity and lower detection power compared to flame—AAS. The reduction of S A is caused mainly by the reduction of b/f D by a factor of about 0.1 and to a smaller degree by stronger broadening of the absorption line and the depopulation of the lower energy state of the atom A that absorbs the resonance radiation. The estimated S A value for A = Ag, Al, Ca, Cd, Co, Cr, Cu, Pd and Pt agree with the corresponding experimental values to within a factor of about 3. No experimental values could be obtained for B and Si. An application field of ICP—AAS is the analysis of complex compounds that are difficult to dissociate into atoms using flames. In these determinations, a high sensitivity is generally not needed but a good selectivity is important. Some applications are shown.

Selective absorption and spontaneous emission in a resonator

A theoretical analysis is made of the influence of spontaneous radiation on the sensitivity of the method of continuous detection of an absorption line in which an absorption cell is placed inside a laser resonator. It is shown that this influence is negligible if the laser modes are coupled not only to the common reservoir of atoms or molecules but each mode additionally acquires energy from its own reservoir. If the contribution of the individual reservoirs to the total energy balance is small compared with the contribution of the common reservoir, the probability of spontaneous emission determines the maximum possible sensitivity of this absorption measurement method.

Surface ionization of indium and aluminum on iridium

Atomic beams of In and A1 were ionized on a heated Ir surface in a good vacuum. Curves of ion current density versus reciprocal surface temperature are plotted with atomic reservoir temperature as parameter, yielding also desorption energies of 4 to 5 eV. Ion current densities from [inverted lazy s] 10−9 to 10−6 A/cm2 were measured in the temperature range from [inverted lazy s] 1400 to above 2000°K. The calculated ionization efficiency for the system In on Ir is about 40% taking into account excited atomic states.

Chemiluminescent Reactions of Major Importance for the Upper Atmosphere

AbstractA huge reservoir of oxygen atoms (and to a minor extent nitrogen atoms) is present in the upper atmosphere, extending upward from about 100 kilometers. This abundance of atoms would be sufficient for substantial illumination of the night sky if appropriate reactions could be found. In the pressure region of 1 millimeter to an atmosphere, the 2‐body collision reactions yielding light play a minor role. At pressures substantially below one millimeter, these reactions become dominant and may be the answer for this problem. A series of reactions, including nitrogen and sulfur compounds, the resulting light emission, and related problems are discussed.