Metastable Argon Ions Research Articles

Long-lived Ar-Hg plasma in the afterglow of a high-current pulsed discharge

High-density (n > 1012 cm−3) argon-mercury plasma produced by a short (t ∼ 20 μs) high-power pulsed discharge in argon with an admixture of mercury vapor at a discharge current of ∼50 A, an argon pressure of ∼4 mm Hg, and a mercury vapor pressure of ∼10−3 mm Hg was studied using optical spectroscopy and radio physics methods. It is found that the lifetime of this plasma after the end of the discharge pulse is up to 10−2 s. It is shown that such an abnormally long lifetime of such an afterglow plasma, as compared to the plasma of an argon discharge without an admixture of mercury vapor, is related to the long residence time of atoms and ions of both argon and mercury in highly excited states due to chemi-ionization processes involving long-lived metastable argon ions. It is suggested that dissociative recombination of highly excited molecular ions of argon play an important role in the transfer of excitation to argon atoms and ions that are close to autoionization states.

Experimental studies of transverse metastable ion velocity distribution functions in the presheath of a weakly collisional argon plasma

Laser-induced fluorescence measurements of the transverse metastable ion velocity distribution function near a negatively biased plate in a low temperature (Te<1eV), low pressure (p0<1mTorr) dc multi-dipole argon discharge plasma have been made with a diode laser. The metastable argon ions in the 3s23p4(P3)3d4F7∕2 state are found to be characterized by a Maxwellian temperature transverse to the direction normal to the plate. For a neutral pressure of 0.3mTorr, the transverse temperature increases along the presheath from 0.026eV in the bulk plasma to 0.058eV at the presheath sheath boundary.

Diode laser-induced fluorescence measurements of metastable argon ions in a magnetized inductively coupled plasma

Velocity distribution functions of metastable argon ions (3d′4F7∕2) have been measured to obtain metastable ion density and temperature by the diode laser-induced fluorescence (LIF) technique in magnetized inductively coupled plasma as a function of pressure, rf power, and magnetic field strength. Calculated density from a rate equation agrees with the trends observed in the experimental data. From the calculation, the metastable ion density should be over 107cm−3 to obtain a LIF signal. From a dc bias experiment, it is suggested that the spatial potential can be the dominant ion heating source, and a simple global model for ion temperature is constructed. In this model, approximately 0.01% and 10% of total spatial potential energy can contribute to ion and neutral temperatures, respectively. The measured ion temperature agrees with the calculation.

Legendre functions and the theory of hole burning

Based on the momentum method the Fokker-Planck equation is derived for a velocity distribution perturbed by monomode laser excitation (hole burning). If the used collision kernel applies to marked forward scattering and if the collision partner is assumed to be infinitely heavy, the FPE degenerates into the Legendre equation. While a proportional term accounts for the decay of atoms, an inhomogeneity accounts for their creation. The considered species is metastable argon ions. These ions are probably created by electronic ionization, while both electronic deexcitation and metastability exchange interfere in their destruction. The laser keeps the solution of the FPE at zero level for any velocity whose component along the laser beam upsilon z,0 follows from the laser frequency by the Doppler condition. We treat this constraint as a boundary condition for the solution. The latter is put up as a superposition of the Legendre function which solves the homogeneous part, with a special solution of the inhomogeneous equation. Free parameters are adjusted to the boundary condition. The thus obtained solution is finally integrated over all the velocity groups of atoms which under our assumptions are not coupled collisionally, to yield the expected shape of the signal. The velocity groups were assumed to be distributed according to Maxwell. We devised two types of experiments to measure the shape of the hole. Both are suited to measure holes on the wings as well as on the centre of the line. Remarkable similarity of the measured and the calculated signals is found.

Hole burning and optical pumping by single-mode laser light

A differential equation for the evolution of Bennet holes in a Maxwell distribution is derived on the basis of the Boltzmann equation. Characteristic forms of these holes are obtained with a sharp peak at the laser frequency and exponential wings attached to it. An experiment to verify the presence of these holes during optical pumping of metastable argon ions is reported here. Electro-optic modulation of the laser light represents a valuable method of overcoming the limit set by hole burning with regard to laser pumping.

Time-of-Flight Study of Low Energy Charge Transfer Reactions of Ar Ions and Metastable Ar Ions with H2 Molecules

Translational energies of secondary neutral atoms produced by the charge transfer reactions in collisions of argon ions Ar + and metastable argon ions Ar +M with H 2 . molecules have been measured by a time-of-flight technique at ten eV region. Two kinds of charge transfer processes were examined; reaction between ground state reactants Ar + +H 2 →Ar+H 2 + , and formation of metastable atoms Ar M from metastable ions Ar +M +H 2 →Ar M +H 2 + . The ground state Ar atoms were predominantly scattered with little or no angular deflection and with little energy exchange, resulting the H 2 + in vibrational state v '=1 for Ar + ( 2 P 3/2 ) and v '=2 for Ar + ( 2 P 1/2 ). On the other hand, the Ar M atoms were yielded with being deflected in relatively wide angle and releasing considerable amount of internal energy (≥1 eV).

Study of Low Energy Charge Transfer Reactions of Metastable Ar Ions with Ar, Kr and Xe Atoms by Time-of-Flight Technique

Energy distributions of metastable argon atoms Ar M produced by charge transfer collisions of metastable argon ions Ar +M with Ar, Kr and Xe were measured by a time-of-flight technique at 10 eV region. The Ar M 's were found to be formed by only exothermic reactions. The analysis of the energy distributions revealed that in any case, certain excited states of atom Ar * are produced by the collisions and Ar M follows via the radiative decay from the Ar * presumably of the 3p 5 3d state. A hypothesis of one-electron-process for the charge transfer is proposed.

Charge transfer excitation in low energy collisions between rare gas ions and cadmium atoms

Excited state production in collisions between rare gas ion and cadmium atoms has been studied in a crossed beam apparatus at kinetic energies as low as 2 eV. It was found that charge transfer excitation cross sections resulting from impact of metastable argon ions were considerably larger than those with other rare gas ion reactants, either ground or excited state. The selective population of CdII (6s 2S) in these low energy Ar+/Cd interactions suggests that, under the proper conditions, laser action at 257.3 and/or 274.9 nm might be possible.

Study of Low Energy Charge Transfer Reactions of Metastable Argon Ions with Argon Atoms by Time-of-Flight Technique

A new technique for kinematical study of low energy charge transfer reactions is demonstrated with the reaction Ar +M +Ar→Ar M +Ar + + Δ E , where the suffix M denotes metastable states of each species. The product metastable argon atoms Ar M can be detected with a secondary electron multiplier even at very low energy, and the energy distribution of Ar M is measured by time-of-flight technique with a high resolution. The energy defect Δ E of the above reaction was determined to spread through 2 to 5 eV (exothermic). A discussion about the results obtained is given.

Energy-transfer reactions of metastable argon ions with krypton in a flowing afterglow

Abstract Light emissions were observed from Kr(6p) produced in the flowing-afterglow reaction of Kr with active ionic species of argon, which were ascribed to the metastable states. Ar+M. Relative quenching rates of ArM and Ar+M by Ar and N2 were examined: Ar quenches Ar+M more effectively than ArM, whereas N2 quenches ArM more effectively than Ar+M.

Emission spectra of CH(A 2Δ) from methane in an argon flowing afterglow

The CH A 2ΔX 2Π emission was observed in the flowing afterglow reaction of charged species of argon with CH 4. Energetic considerations show that metastable argon ions, Ar +M( 4D, 4F, 2F, 2G, are plausible candidates, although the contribution of Ar 2+ cannot be completely excluded. The CH A 2ΔX 2Π spectrum was analyzed; the ratio of vibrational populations for the υ′ = 0 and 1 states, P vib(υ′ = 0), is estimated to be 0.56 ± 0.17, and the effective rotational temperatures are (3.0 ± 1.5) × 10 3 and (1.7 ± 0.4) × 10 3 K, respectively.

Role of metastable argon ions in Ari++Ar charge-exchange collisions

The cross sections sigma 21 at Elab=21 keV and sigma 12 at Elab=36 keV for argon ions in argon are measured using two different production mechanisms for the incident projectile ions: direct extraction from an ion source and generation by charge exchange, respectively. It is found that long-lived metastable ions are produced by the latter method, which influence the measured cross section appreciably.