Ar 4s Research Articles

Radiative lifetimes and collisional energy transfer rate constants in Ar of the Ar(3p55p) and Ar(3p55p′) states

The radiative lifetimes and collisional deactivation rate constants of Ar[3p5(2P01/2)5p] and Ar[3p5(2P03/2)5p] levels with argon atoms have been measured by time resolved laser induced fluorescence combined with a pulsed discharge for preparation of populations in the Ar(4s) precursor levels. The radiative lifetimes of Ar(5p) levels are 100–140 ns, and their two-body deactivation rate constants are in the range of (1.2–5.6)×10−10 cm3 atom−1 s−1. About half of the two-body energy transfer is intramultiplet relaxation. Only about 20% of the Ar(5p) radiative decay is via 5p–4s transitions; the reminder is via transitions to the 5s and 3d states. The radiative cascading through the 5s and 3d states populates the 4p states with conservation of the inner core configuration. From the time dependence of the emission intensities from the 4p levels, the radiative lifetimes of the 5s and 3d states were estimated to be ∼50 ns.

Bimolecular and ‘‘three-body’’ quenching of paschen-1s argon atoms by N2, H2, and O2 and effects of N2 on the yield of the first triplet argon excimer

Rate constants for bimolecular quenching of Ar (1s) resonance-state and metastable atoms by N2, H2, and O2 have been measured by fast absoprtion spectrophotometry at argon pressures in the 102–103 Torr region at 298 K. ’’Three-body’’ quenching attributed to collisional relaxation of vibrationally excited dissociative excimer molecules by molecular quenching agents has been observed to occur efficiently for all Ar (1s) atoms in the presence of H2 and O2, but only for the resonance-state Ar (1s) species in the presence of N2. A discussion and analysis of the temporal behavior and the yield of Ar2 (3S+u) molecules in the context of the mechanism for Ar (1s) atom decay and excimer formation indicates that the predominant precursors of the first triplet argon excimer in Ar/N2 mixtures are probably Ar (3P2) atoms and Ar2 van der Waals molecules, the latter through the agency of N2 (C 3Ru) at higher N2 concentrations.

Quenching of the lowest-lying metastable excimer of argon by N2 and effects of ’’three-body’’ Ar(1s) quenching on the yield of Ar2(3Σ+u)

Fast absorption spectrophotometry has been used to monitor the growth and decay of the Ar2(3Σ+u) excimer species at 992 nm in argon–nitrogen mixtures following passage of single pulses of a high current, high energy electron beam. The rate constant for electronic energy transfer to N2 is equal to 2.24 (±0.08)10−12 cm3 molecule−1 s−1 at 294 K. The yield of Ar2(3Σ+u) is found to be markedly enhanced relative to predictions based on the total quenching efficiencies of N2 for the Ar(1s) atoms. This enhancement is attributed to ’’three-body’’ quenching by N2, i.e., vibrational and rotational relaxation of dissociative excimer molecules formed by two-body Ar(1s)+Ar(1S0) combinations.

Single-electron ionisation of Ar 3s2subshell by slow electrons

The effect of the self-consistent atomic field and atomic-electron correlations upon the magnitude and the form of the total cross section is considered theoretically. The calculations were performed in the Hartree-Fock approximation taking account of many-electron correlations for the incoming electron energy region from the ionisation threshold up to 100 eV. It has been found that consideration of the action of the atomic self-consistent field upon the incoming and scattered electrons, the exchange effects and the final-state configuration interaction is more essential than the correlation corrections within the RPAE.

Kinetics and mechanisms for the decay of Paschen (1s) resonance state argon atoms

Measurements of effects of pressure and temperature on the decay constants of excited Ar atoms (3p54s1) have been made in electron beam pulse irradiated Ar gas (100–700 Torr) by means of fast absorption spectrophotometry. Interpretation of the pressure and temperature dependence of the decay constants leads to the conclusion that the resonance state Ar (1s) species decay via formation of electronically excited molecular intermediates in this pressure range. The resonance state atoms are shown to decay in a manner consistent with a sequence of elementary steps involving collisional stabilization and radiative decay of excited molecules. Observed small positive temperature coefficients of all Ar (1s) species are attributed to effects of temperature on collision frequencies with virtually zero energies of activation at 153 to 300 K.

Energy transfer between electronically excited argon and nitrogen: A kinetic model for the 3371 and the 3577 Å laser emissions

Laser action of an argon–nitrogen mixture excited by an electron beam has been studied. We report laser action at 3577 Å, but also at 3371 Å. In previous kinetic models laser emission at 3371 Å was forbidden. In this paper we present a new kinetic model based on a total transfer reaction between Ar (4s) and N2(C 3Πu). The main feature of our model is to permit laser action at 3371 Å only if the excitation time is short enough. The experiments performed with a small electron gun possessing the required characteristics (risetime=1 ns FWHM=10 ns) permitted us to observe laser emissions at 3371 and 3577 Å. For strong cavity coupling the emission is more powerful on the 3371 line than on the 3577 Å line. The same experiments made with an electron gun of a larger energy and a longer excitation pulse exhibits only a laser emission at 3577 Å, in agreement with theoretical computations.

Near-Resonant Electronic Energy Transfer from Argon to Hydrogen

The argon sensitized fluorescence of molecular hydrogen has been observed. Relative cross sections have been determined for transitions of the type H2(X 1Σg +, v=0, J) + Ar* → H2(B 1Σu +, v′, J′) + Ar + Δ E,where Ar* is either Ar 4s[112]J=1 0 or Ar 4s′[12]J=1 0 and the hydrogen molecules, H2, D2, and HD are initially thermally distributed among J states at 300 ± 30°K. Calculations indicate that the largest cross sections, on the order of gas kinetic or larger, are due primarily to long range dipole-dipole interactions. These cross sections are for transitions for which | Δ E | 〈 100 cm−1 when Δ J ≡ J′ − J=± 1. The long range dipolar calculations establish an absolute magnitude scale for the cross sections. A curve crossing mechanism is possible for negative ΔE and provides a plausible explanation for the remaining levels excited. Generally, only one vibrational level of the hydrogen molecule is excited by each argon state. This contrasts sharply with many previous sensitized excitation experiments in which most of the energetically accessible energy levels are excited.