Ni. Butkovskaya et Dw. Setser, 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, Journal of physical chemistry, 100(12), 1996, pp. 4853-4866
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.