Refined representation of falloff curves for the reaction HO + NO2 + N2 → (HONO2, HOONO) + N2.

Experimental data for the reactions (1) HO + NO2 (+N2) → HONO2 (+N2) and (2) HO + NO2 (+N2) → HOONO (+N2) near 300 K and over the pressure range 1 Torr to 320 bar are represented in terms of novel asymmetric broadening factors in falloff expressions. This analysis allows for a refined representation of the data, reproducing fine details of k = k1 + k2 and k2/k1 and probably allows for a better extrapolation to the limiting low and high pressure rate constants than possible with symmetric broadening factors in conventional falloff expressions. The experimental data clearly show that the center broadening factor Fcent,1 is close to 0.41 and consistent with results from theoretical modeling. This value of Fcent markedly differs from the “standard value” of 0.6, and the consequences of this difference are illustrated. Limiting rate constants of k1,0 = [N2] (T/300 K)−4.5 3.2 × 10–30 cm6 molecule–2 s–1, k2,0 = [N2] (T/300 K)−4.5 1.0 × 10–31 cm6 molecule–2 s–1, k1,∞ = 2.7 × 10–11 cm3 molecule–1 s–1, and k2,∞ = 4.8 × 10–11 cm3 molecule–1 s–1 are obtained and tested over the range 220–300 K, whereas the exponent −4.5 changes to −3.0 in k1,0 and k2,0 over the range 300–430 K (the values correspond to falloff curves with asymmetric broadening factors)