Kinetics of NCl(aΔ) via Photodissociation of ClN3

Kinetic measurements of NCl(a1Δ) metastables produced by the photolysis of chlorine azide (ClN3) at 193 nm are reported. High NCl(a1Δ) density (>1015 molecules/cm3) production facilitates measurements of the NCl(a1Δ) + NCl(a1Δ) self-annihilation rate. A gas phase transient chemical titration scheme is used to calibrate absolute NCl(a1Δ) density. The NCl(a1Δ) bimolecular rate coefficient at room temperature is (7.2 ± 0.9 × 10-12 cm3/(molecule s) and has a magnitude very critical to the development of an NCl(a1Δ) + I(2P3/2) → I*(2P1/2) + NCl(X3Σ-) chemical laser. Despite the large value of the self-annihilation rate, intense I*(2P1/2) emission via transfer from NCl(a1Δ) is strongly observed when mixtures of CH2I2 and ClN3 are photolyzed at 193 nm. Unlike the analogous O2(a1Δ) + I(2P3/2) energy transfer system, the relatively large NCl(a1Δ) bimolecular rate constant suggests that NCl(a1Δ) transport times must be short and will require small chemical mixing regions for efficient lasing. In addition, the 300 K collisional quenching rate constants of NCl(a1Δ) by F2, Cl2, and Br2 are (2.5 ± 1.1) × 10-13, (2.9 ± 0.6) × 10-11, and (1.4 ± 0.2) × 10-10 cm3/(molecule s), respectively.