CHEMICAL-DYNAMICS OF H ABSTRACTION BY OH RADICALS - VIBRATIONAL-EXCITATION OF H2O, HOD, AND D2O PRODUCED IN REACTIONS OF OH AND OD WITH HBRAND DBR

Infrared chemiluminescence from vibrationally excited H2O, HOD, and D2 O molecules in the ranges 3200-3900 cm(-1) (O-H stretch) and 2400-2900 cm(-1) (O-D stretch) was observed from the reactions of OH and OD rad icals with hydrogen and deuterium bromide in a fast flow reactor with 0.5-2 Torr of Ar carrier gas at 300 K. Hydroxyl radicals were produced via the H + NO2 reaction; the H atoms were generated by microwave dis charge in a H-2/Ar mixture. Vibrational distributions for H2O, HOD, an d D2O were determined by computer simulation of the experimental emiss ion spectra. The H2O emission from OH + HBr reaction shows inverted po pulations for both the collisionally coupled stretching modes and the bending mode. Inversion in the bending distribution with a maximum for v(2) = 1 is more apparent in the v(1.3) = 1 level, which is populated up to the thermochemical limit of v(2) = 5. The HOD emission from OD + HBr shows an inverted population in the O-H stretching mode with a m aximum for v(3) = 2 and shows a decreasing population in the collision ally mixed O-D stretching/bending v(1,2) levels with half the molecule s in the v(1) = 0 group. The distribution in v(1,2) for HOD from the O H + DBr reaction also appeared to be decreasing for v(1) > 0 levels, b ut collisional redistribution to v(3) = 1 seems evident from the press ure dependence of the vibrational distributions. These distributions a re discussed with the aid of the information theoretic analysis and co mpared to F atom abstraction reactions from HBr and DBr and to quantum -scattering calculations on an OH + HBr surface. The overall vibration al energy disposal is [f(v)] approximate to 0.6, which resembles the a nalogous three-body cases. However, the partitioning of the energy bet ween stretching and bending modes raises new questions about reaction dynamics.