Quenching cross sections for electronic energy transfer reactions between metastable argon atoms and noble gases and small molecules

Abstract

Reaction rate constants for the quenching of electronic energy in metastable argon (3P0,2) by Kr, Xe, and a number of simple molecules have been measured. A hollow, cold-cathode discharge excites the metastables in a flow apparatus. The concentration of metastables was followed by absorption spectroscopy as a function of time and of quenching molecule concentration. Quenching of Ar*(3P2) by Kr, CO, N2, CF4, and H2(D2) proceeds at rates between 0.6 and 7 × 10−11 cm3 molecule −1 · sec−1. Except for Kr, Xe, N2, CO, and CH4, the 3P0 metastable level is quenched slightly more rapidly than the 3P2 level. With the aid of data in the literature, the contribution from the product channels (Penning and associative ionization) are considered for quenching by NO and C2H2. These channels appear not to be of major importance for quenching since the ionization efficiency of these two reactions is low: ∼ 0.2 for NO and ∼ 0.1 for C2H2. The quenching mechanism is discussed in terms of both a curve crossing and a ``golden rule'' rate law; the latter appears to be favored.

Validity of actinometry to measure N and H atom concentration in N2-H2direct current glow discharges

“…However, the metastable states of argon, 3 P 0 and 3 P 2 , are efficiently quenched by H 2 , N 2 , N and H, see table 1, and the population of these states in the discharge is negligible [9][10][11][12].…”

Comment on ‘‘Effect of electron temperature on negative hydrogen ion production in a low-pressure Ar discharge plasma with methane’’ [Appl. Phys. Lett. 63, 1619 (1993)]

“…For the quenching of the 3 P 0 and 3 P 2 states of Ar by CH 4 , the cross section values are 45 and 74 Å 2 , respectively. 6 Therefore, CH 4 ** states are efficiently populated via this mechanism and they attach low-energy electrons dissociatively producing H Ϫ and CH 3 , i.e., e Ϫ ϩCH 4 **→H Ϫ ϩCH 3 . It has been recently shown 7 that electron attachment to laser-excited superexcited states ͑electronically excited states lying above the ionization threshold͒ of CH 4 is extremely efficient.…”

Quantitative evaluation of the densities of active species of N2 in the afterglow of Ar-embedded N2 RF plasma

“…Thus, it can be concluded that very similar gas temperatures are achieved at lower RF powers by mixing N 2 with Ar. It is here mentioned that the Ar metastable atoms can excite the N 2 molecules [25] at low N 2 percentage (<1%) in Ar [33] producing an overpopulation of high rotational states of N 2 (C, v 0 ¼ 0). As such an overpopulation of rotational states has not been reported for the N 2 (B,v 0 ) states, it is here estimated that the rotational temperature of the N 2 (B,v 0 ¼ 2) state in Ar-20%N 2 gas mixtures is near the gas temperature.…”