Kinetics of the gas phase reaction OH+NO(+M)->HONO(+M) and the determination of the UV absorption cross sections of HONO

The reaction OH + NO(+ M) --> HONO(+ M) with M = SF6 as a third body has been employed as a clean source for recording the near-ultraviolet absorption spectrum of HONO without interference from other absorbing species. The reaction was initiated by the pulse radiolysis of SF6/H2O/NO mixtures with total pressures in the range 10-1000 mbar at 298 K. The pressure dependence of the rate coefficient was studied by time-resolved UV and IR spectroscopy. By analysis of the fall-off curve we have derived a value for the limiting low pressure rate constant k(0)/[SF6] = (1.5 +/- 0.1) X 10(-30) cm(6) molecule(-2) s(-1) at 298 K, using the values of k(infinity) = (3.3 +/- 0.3) X 10(-11) cm(3) molecule(-1) s(-1) and F-cent = 0.81 reported by Tree and co-workers. The UV spectrum of HONO was recorded in the range 320-400 nm and an absolute absorption cross section of sigma = (5.02 +/- 0.76) X 10(-19) cm(2) molecule(-1) has been determined for the strongest band of HONO located at 354.2 nm. Differential absorption cross sections to be used for field measurements of HONO were also investigated. (C) 1997 Elsevier Science B.V.