SEQUENTIAL 2 (BLUE) PHOTON-ABSORPTION BY NO2 IN THE PRESENCE OF H-2 AS A SOURCE OF OH IN PULSED PHOTOLYSIS KINETIC-STUDIES - RATE CONSTANTSFOR REACTION OF OH WITH CH3NH2, (CH3)(2)NH, (CH3)(3)N, AND C2H5NH2 AT295 K

The use of the sequential two-photon dissociation of NO2 (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 NO2 at these wavelengths leads to both O(D-1) and O(P-3) production ((40% and 60%, respectively); th e O(D-1) is rapidly converted to OH in the presence of approximate to 1 x 10(16) cm(-3) H-2 [O(D-1) + H-2 --> OH + H] The H atom reacts with NO2 to generate a further OH radical (H + NO2 --> OH + NO). Laser flu ences of approximate to 20-40 mJ cm(-2) were used to generate between 2 x 10(11) and 1 x 10(12) cm(-3) OH from an initial NO2 concentration of (5-13) x 10(14) cm(-3). OH [and O(P-3)] were detected by resonance fluorescence. Rate constants for the reactions of some aliphatic amine s with the OH radical have been obtained at 295 K. The results obtaine d (in cm(3) s(-1)) are k(OH + CH3NH2) = (1.73 +/- 0.11) x 10(-11), k(O H + (CH3)(2)NH) = (6.49 +/- 0.64) x 10(-11), k[OH + (CH3)(3)N] = (3.58 +/- 0.22) x 10(-11), and k(OH + C2H5NH2) = (2.38(-0.15)(+0.5)) x 10(- 11). Data for (CH3)(2)NH were also obtained using the 193 nm photolysi s of N2O/CH4 as the O(D-1) source; the rate constant above is the aver age value obtained using both methods. The error limits include both s tatistical (2 sigma) and systematic errors.