Infrared Spectroscopic and Kinetic Characterization on the Photolysis of Nitrite in Alcohol-Containing Aqueous Solutions.

Nitrite is regarded as a potential OH and NO precursor in aqueous solution upon ultraviolet photolysis. A step-scan Fourier-transform interferometer was employed to collect the transient infrared difference spectra upon excitation of the sodium nitrite aqueous solution in the presence of methanol and ethanol upon 355 nm pulsed excitation. The photolytic intermediates were proposed to be NO and NO via the direct dissociation from NO and the rapid reaction of OH and NO, respectively. Coupled with the theoretical calculations of the absolute energies and harmonic wavenumbers of relevant species using B3LYP density functional theory with the CPCM model to account for the medium effect of HO, a transient band at 1860-2030 cm could be attributed to dissolved NO isomers that could be quickly generated from NO + NO. On the basis of the predicted thermodynamics, the reactions of alcohols with NO were less thermodynamically favorable than that of water, resulting in a slightly decelerated depletion rate of NO in alcohol-containing aqueous solution. Comparing the transient population of NO in the absence and presence of CHOH or CHOH, the upper-bound bimolecular rate coefficient of NO or NO with alcohols is reported as 7.3 × 10 M s for the first time. The spectroscopic and kinetic evidence of the reactivity of alcohols with NO, NO, and NO are provided to augment the roles of alcohols and NO in solution or in aqueous aerosol photochemistry.