KINETICS OF THE GAS-PHASE REACTION OH-]HONO(+M) AND THE DETERMINATIONOF THE UV ABSORPTION CROSS-SECTIONS OF HONO(NO(+M))

The reaction OH + NO(+ M) --> HONO(+ M) with M = SF6 as a third body h as 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-re solved UV and IR spectroscopy. By analysis of the fall-off curve we ha ve derived a value for the limiting low pressure rate constant k(0)/[S F6] = (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 spec trum of HONO was recorded in the range 320-400 nm and an absolute abso rption cross section of sigma = (5.02 +/- 0.76) X 10(-19) cm(2) molecu le(-1) has been determined for the strongest band of HONO located at 3 54.2 nm. Differential absorption cross sections to be used for field m easurements of HONO were also investigated. (C) 1997 Elsevier Science B.V.