Study of elementary reactions by atomic resonance absorption with a non-reversed source. Part 2.—Oscillator strengths for Cl 4s-3p5 transitions and rate constants for specific product channels from Ar (3P2,0)+ Cl

Abstract

Energy transfer processes resulting in formation of highly excited CI atoms have been investigated in the collisions of Ar*(³P_{2, 0}) metastable atoms with ground state molecular Cl₂ and atomic Cl(3p⁵). Vacuum ultraviolet spectrometry has shown that excited Cl (4s) atoms are formed as major exit channels of both the Ar*+ Cl₂ and Ar*+ Cl interactions. Whilst the Cl (4s) atoms from Ar*+ Cl₂ were thermal at 300 K, varying amounts of excess kinetic energy were found in the Cl (4s) atoms from Ar*+ Cl, as expected if 4s atoms are formed directly from Ar*+ Cl and not via cascade from higher energy states of Cl. The major exit channel for Ar*+ Cl forms Cl (4s) atoms, but additional channels exist for the formation of the more highly excited 4s′, 3d and 5s states of Cl. The total rate constant for formation of 4s, 4s′, 3d and 5s chlorine atoms is (2.1 ± 0.7)× 10^–10 cm³ molecule^–1 s^–1 at 300 K.

The strong emission of thermal, non-reversed, 4s-3p⁵ Cl atom resonance lines from Ar*+ Cl₂ has been utilized as a source for absorption measurements on Cl (3p⁵) atoms. Measurements of line absorption intensity as a function of ground state Cl atom particle density have been used to determine the oscillator strengths ƒ(λ/nm) for all nine lines of the 4s^{2, 4}P_J-3p⁵²P_J multiplet transitions: ƒ(133.6)=(2.8 ± 0.6)× 10^–2; ƒ(135.2)=(9.3 ± 1.6)× 10^–2; ƒ(134.7)=(1.0 ± 0.3)× 10^–1; ƒ(136.3)=(3.8 ± 0.6)× 10^–2; ƒ(137.3)=(7.9 ± 4.8)× 10^–5; ƒ(138.996)=(9.4 ± 6.6)× 10^–4; ƒ(138.0)=(2.4 ± 0.5)× 10^–3; ƒ(139.6)=(5.8 ± 1.8)× 10^–3; ƒ(138.969)=(1.4 ± 0.1)× 10^–4.