No abstract

No abstract

No abstract

The surface reaction of NO2 and H 2 0 vapor to emit HONO into the gas phase was studied in the evacuable and bakeable photochemical chamber under the irradiation of UV-visible light ( 2 290 nm). Kinetic analysis of the NO, NOz, and HONO with the aid of computer modeling strongly suggested that the formation of HONO by the surface reaction is photoenhanced. When a linear regression was assumed, the photoenhancement factor defined by {(kh1/k2,) -1) was expressed as (6.8 ? 2.5)k1 under our experimental conditions, where k , is the primary photolysis rate of NO,, and k2,, k h are the second-order-equivalent rate constants of the HONO formation reaction in dark and under irradiation, respectively. The discussion was made that this photocatalitic enhancement of HONO formation would explain the nature of the extra OH radical flux in the smog chamber experiments, which has been discussed as "unknown radical source" and has still been unexplained by the surface dark reaction of NOz and H 2 0 to emit HONO.

Rate constants for the reaction of atomic oxygen with ketene, and methyl, ethyl, and dimethyl ketene were measured over a temperature range of 230--449 K using the pulse radiolysis resonance absorption system. Over the temperature range of the experiments, the rate data could be fitted by Arrhenius expressions:(4.79± l.31)X 1O-'2exp[(494.9± 163.2 cal mol-')IRT]; 0 + (C 2 H s )CHCO, (5.36±0.83)X 1O-'2exp[(444.6±94.0 cal mol-')lRT]; 0 + (CH,hCCO, (5.92 ±0.94) X 1O-'2exp[(1131 ±85 cal mol-')IRT]; in units of cm' molecule-' s-'.The rate constants at room temperature were also determined using a discharge-flow system coupled toa photoionization mass spectrometer. Rate constants obtained are 0.D43±0.D4, 1.l6±0.13, l.36±0.l1, and 6.04±0.64X 10-11 cm-' molecule-' s-, for CH 2 CO, (CH,)CHCO, (C 2 H s )CHCO, and (CH 3 hCCO, respectively. Several reaction products were analyzed by the photoionization mass spectrometer.