RATE CONSTANTS FOR INTERACTION OF ¹O₂¹Δg) WITH AZIDE ION IN WATER

The rate constant for quenching of 1 O 2 by azide ion in water was determined to be (5.0 ± 0.4) × 10 8 M −1 s −1 using a variety of sensitizers (including humic acids) and 1 O 2 acceptors. The apparent second‐order rate constant decreases with pH below pH 5.5 in accordance with the protonation of azide ion to form hydrazoic acid (p K a = 4.6). Quenching by hydrazoic acid is at least 2 orders of magnitude slower than by azide ion. Greater than 99% of all interactions between 1 O 2 and azide ion involve physical quenching rather than chemical reaction. Humic acid triplets are not significantly quenched by azide ion at concentrations less than 2 m M , allowing azide ion quenching to be used as a diagnostic test for the intermediacy of 1 O 2 in photosensitized oxidations in natural surface waters.