Sequential Two (Blue) Photon Absorption by NO₂ in the Presence of H₂ as a Source of OH in Pulsed Photolysis Kinetic Studies:  Rate Constants for Reaction of OH with CH₃NH₂, (CH₃)₂NH, (CH₃)₃N, and C₂H₅NH₂ at 295 K

The use of the sequential two-photon dissociation of NO 2 (420−450 nm) in the presence of H 2 as a novel source of OH in kinetic studies has been assessed. Two-photon absorption by NO 2 at these wavelengths leads to both O( 1 D) and O( 3 P) production ((40% and 60%, respectively); the O( 1 D) is rapidly converted to OH in the presence of ≈1 × 10 16 cm -3 H 2 [O( 1 D) + H 2 → OH + H]. The H atom reacts with NO 2 to generate a further OH radical (H + NO 2 → OH + NO). Laser fluences of ≈20−40 mJ cm -2 were used to generate between 2 × 10 11 and 1 × 10 12 cm -3 OH from an initial NO 2 concentration of (5−13) × 10 14 cm -3 . OH [and O( 3 P)] were detected by resonance fluorescence. Rate constants for the reactions of some aliphatic amines with the OH radical have been obtained at 295 K. The results obtained (in cm 3 s -1 ) are k (OH + CH 3 NH 2 ) = (1.73 ± 0.11) × 10 -11, k (OH + (CH 3 ) 2 NH) = (6.49 ± 0.64) × 10 -11, k [OH + (CH 3 ) 3 N] = (3.58 ± 0.22) × 10 -11, and k (OH + C 2 H 5 NH 2 ) = (2.3 ) × 10 -11 . Data for (CH 3 ) 2 NH were also obtained using the 193 nm photolysis of N 2 O/CH 4 as the O( 1 D) source; the rate constant above is the average value obtained using both methods. The error limits include both statistical (2σ) and systematic errors.