Kinetic measurements of NCl(a 1 ∆) metastables produced by the photolysis of chlorine azide (ClN 3 ) at 193 nm are reported. High NCl(a 1 ∆) density (>10 15 molecules/cm 3 ) production facilitates measurements of the NCl(a 1 ∆) + NCl(a 1 ∆) self-annihilation rate. A gas phase transient chemical titration scheme is used to calibrate absolute NCl(a 1 ∆) density. The NCl(a 1 ∆) bimolecular rate coefficient at room temperature is (7.2 ( 0.9 × 10 -12 cm 3 /(molecule s) and has a magnitude very critical to the development of an NCl(a 1 ∆) + I( 2 P 3/2 ) f I*( 2 P 1/2 ) + NCl(X 3 Σ -) chemical laser. Despite the large value of the self-annihilation rate, intense I*( 2 P 1/2 ) emission via transfer from NCl(a 1 ∆) is strongly observed when mixtures of CH 2 I 2 and ClN 3 are photolyzed at 193 nm. Unlike the analogous O 2 (a 1 ∆) + I( 2 P 3/2 ) energy transfer system, the relatively large NCl(a 1 ∆) bimolecular rate constant suggests that NCl(a 1 ∆) 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(a 1 ∆) by F 2 , Cl 2 , and Br 2 are (2.5 ( 1.1) × 10 -13 , (2.9 ( 0.6) × 10 -11 , and (1.4 ( 0.2) × 10 -10 cm 3 /(molecule s), respectively.