Rate constants for collision-induced emission of O2(a1Δg) with He, Ne, Ar, Kr, N2, CO2 and SF6 as collisional partners

Abstract

Rate constants for singlet oxygen collision induced emission of the a¹Δ_g–X³Σ⁻_g transition at 1.27 μm were measured for CO₂, N₂, SF₆, and rare gases as collisional partners. Photolysis of ozone by 266 nm laser radiation produced singlet oxygen. We performed direct measurements of pressure dependences of the 1.27 μm emission intensity for partner gases. The measured rate constants k^M_a–X in the units of 10⁻²⁴ cm³ s⁻¹ are as follows: CO₂ – 10 ± 2; N₂ – 3.2 ± 0.6; SF₆ – 7 ± 1; He – 1.1 ± 0.3; Ne – 1.3 ± 0.3; Ar – 2.8 ± 0.6; Kr – 6 ± 1. The measured values of k^M_a–X are close to the values calculated from absorption measurements. Considering the known rate constants k^M_b–a for the b¹Σ_g⁺–a¹Δ_g transition in the gas phase we found that the ratio k^M_a–X/k^M_b–a was constant and independent of a collisional partner according to the “spin–orbit based” mechanism of intensity borrowing proposed by Minaev (THEOCHEM, 1989, 183, 207). However, this ratio amounted to (1.3 ± 0.2) × 10⁻⁴, which is considerably lower than the theoretically predicted value of (3–6) × 10⁻⁴.