Quenching and self-annihilation rate constants for NCl(a) have been determined using pulsed 248 nm photolysis of ClN3 to generate the metastable. Previous quenching measurements that employed different sources for NCl(a) yielded dramatically different rate constants. The present study provided quenching rate constants for Cl-2, HCl, and H-2 that are in good agreement with the discharge flow measurements of Hewett et al. (J. Phys. Chem. A 2000, 104, 539). Determination of the self-annihilation rate constant required knowledge of the branching fraction for NCl(a) formation for 248. nm photolysis of ClN3. This information was obtained from time-resolved measurements of NCl(X) formation and decay. A lower bound for the branching fraction of 0.7 was determined. Self-annihilation of NCl(a) was studied by using intense photolysis pulses to generate high concentrations of NCl(a). Analysis of the second-order decay component yielded a rate constant of (7.0 +/- 1.5) x 10(-13) cm(3) s(-1). This value is an order of magnitude smaller than the previous estimate.