Rate constants and quenching mechanisms for the metastable states of argon, krypton, and xenon

Abstract

Rate constants have been measured by the flowing afterglow technique at 300 °K for the quenching of Ar(3P2), Ar(3P0), Kr(3P2), and Xe(3P2) by a large number of small molecules. For the same reagent, the magnitudes of the cross-sections usually increase in the series Ar(3P2), Ar(3P0), Kr(3P2), and Xe(3P2). The Ar(3P2) and Ar(3P0) data are compared to results in the literature for these states and to data for Ar(3P1) and Ar(1P1). The set of thermal quenching cross sections are used to test the correlations between the magnitudes of the cross sections and properties of the reagents as predicted by the orbiting, absorbing-sphere, golden rule, and curve-crossing mechanisms for quenching. The best correlation is between the cross sections and the C6 coefficient. The analysis supports the proposition that the orbiting-controlled, curve-crossing model is the general mechanism governing the magnitude of the thermal cross sections for quenching of the metastable states. This model explains the very large quenching cross sections of F2 and OF2 (relative to other molecules composed of first row elements) because covalent–ionic curve crossing occurs outside the conventional orbiting radius. The validity of the simple van der Waals dispersion forces as being the dominant entrance channel interaction between the excited state rare gas atoms and the reagents is discussed.

Plasma-Chemical Kinetics of Film Deposition in Argon-Methane and Argon-Acetylene Mixtures Under Atmospheric Pressure Conditions

“…The electron velocity distribution function (EVDF) in our system is determined on the basis of the emission of nitrogen molecule (equations 1-13). For this 5.60x10 -10 cm 3 ·s -1 (Velazco et al, 1978)) -rate constants for quenching of argon metastable during collision with electron, argon, nitrogen and precursors (methane and acetylene), respectively; A -Einstein coefficient for spontaneous emission (2.38x10 7 s -1 for N 2 (C-B) (Pancheshnyi et al, 2000); 1.52x10 7 s −1 for N 2 + (B-X) (Dilecce et al, 2010)); B1 -branching factor for (3) (value = 0.787) (Zhiglinski, 1994); B2 -branching factor for N 2 (C-B, 0-0) transition by emission from N 2 (C,0) (value = 0.5) (Laux & Kruger, 1992); n e -electron density (cm -3 );…”

Absolute detection of metastable rare gas atoms by a cw laser photoionization method

“…The effective ionization energy of the surface species, the thickness of the adsorbate (multi) layer and the surface topology, and the branching ratio towards electron emission in a Rg* deexcitation process are expected to be important for the observed value of y. We note that non-ionizing deexcitation processes in gas-phase collisions of Ar*, Kr* and Xe* with molecules are known to play a dominant role in many cases [74][75][76][77].…”

“…While numerous rate constants for the destruction of metastable rare gas atoms have been measured [74][75][76][77][83][84][85][86] (notably with the flowing afterglow technique [87]), accurate direct measurements of absolute Penning ionization cross sections are scarce for He* and Ne* [80][81][82] and almost missing for Ar*, Kr*, and Xe* [82]. Therefore, we have started experiments with the aim to establish benchmark cross sections for Penning ionization of suitable target atoms or molecules by state selected metastable Ne*, Ar*, and Kr* atoms [88].…”

“…Moreover, non-ionizing, competing processes, which lead to deexcitation of the metastable atom (e.g. adsorbate dissociation) and which are known to be very important in gas-phase collisions of Ar*, Kr*, and Xe* with molecules [74][75][76][77], are expected to play a decisive role.…”

Summary and outlook of the international workshop on aging phenomena in gaseous detectors (DESY, Hamburg, October 2001)

“…However, Ar(Xe)/CF 4 mixtures have rather poor energy and spatial resolution due to the dissociative electron attachment processes in CF 4 [130]- [132]. Moreover, the CF 4 molecule has a small quenching cross-sections of metastable Ar-states [133] and excited CF 4 molecules emit photons from the far UV to the visible [134]. This results in an intolerable level of afterpulsing in Ar/CF 4 gases even at moderate gas gains.…”