Heterogeneous Reactions of HX + HONO and I 2 on Ice Surfaces: Kinetics and Linear Correlations

Reaction probabilities of gaseous nitrous acid, HONO, with HCl, HBr, and HI treated ice surfaces have been investigated in a fast flow-tube reactor coupled with a differentially pumped quadrupole mass spectrometer (QMS) at 191 K. The reaction probability increases with the HX surface coverage, and the rate is the highest for the HONO reaction on the HI-treated ice surface. Relative rate constants are correlated to the nucleophilic parameter, according to the linear free-energy relationship for this series of heterogeneous reactions on ice surfaces. The correlation was also extended to HOCl + HX(ad) reactions on the ice surface, and it can be used to treat other heterogeneous atmospheric and catalytic reactions. The reaction products ClNO and BrNO were determined by the QMS. INO was found to rapidly convert to I2 on surfaces, and I2 was observed from the reaction of HONO + HI. The uptake coefficient of I2 on the HI-treated ice surface is higher than that for I2 on the water-ice surface.