Comparing the Reactivities of Methanol and Methanediol in the Photolysis of Aqueous Nitrite Solution

Abstract

Ultraviolet irradiation of aqueous nitrite (NO2 –) quickly generates hydroxyl (OH) and nitric oxide (NO) radicals, which are subsequently consumed concomitantly with the generation of N x O y species. Recently, dissolved formaldehyde (CH2O) in aqueous solution (e.g., methanediol, CH2(OH)2), has been regarded as the precursor in the formation of atmospheric formic acid (HCOOH) via the reaction with OH and cascading processes (Nature2021593233237). In this work, a step-scan Fourier transform interferometer was utilized to monitor the time-resolved difference infrared spectra of NaNO2 aqueous solution in the presences of methanediol and methanol upon pulsed irradiation at 355 nm. The fates of the dinitrogen trioxide (N2O3), generated via a series of reactions of OH, NO, and NO2 –, differed in the presences of CH2(OH)2 and CH3OH. The decay of N2O3 via hydrolysis with H2O was retarded more by CH3OH than by CH2(OH)2. The monohydroxyl group of CH3OH does not behave like the hydroxyl group of water, whereas the two hydroxyl groups of CH2(OH)2 can be treated as a water reservoir via the quick equilibrium between H2O and CH2O, further facilitating the hydrolytic solvation reaction of N2O3. The observed difference in reaction kinetics involving hydration should be thoroughly taken into consideration in formaldehyde-related aqueous reactions.

Applications of time‐resolved step‐scan Fourier‐transform infrared spectroscopy in revealing the light‐initiated reactions in condensed phases

“…Small organic molecules such as humic acid and ethanol further consume the OH radical, causing the net depletion of nitrite upon ultraviolet treatment [104]. Recently, we studied the photolysis of nitrite (NO 2 À ) in the presence of methanol, ethanol [58], and methanediol (CH 2 (OH) 2 ) [59,105], which is the hydrated form of formaldehyde [106], to differentiate their reactivities in terms of the lengths of the hydrocarbons, the mono-ol, and diol. We found that the photolysis of neat NO 2 À leads to the generation of [107], an upper-bound bimolecular rate coefficient of methanol and ethanol with NO can be determined [58].…”

“…Accounting for the bimolecular rate coefficients of OH with CH 3 OH and C 2 H 5 OH and the transient population of N 2 O 3 [107], an upper‐bound bimolecular rate coefficient of methanol and ethanol with NO can be determined [58]. In addition, the reactivity of the simplest geminal diol, CH 2 (OH) 2 , which can be prepared by dissolving paraformaldehyde in water [108], was also compared with that of methanol [59]. The previous reports revealed that the bimolecular rate coefficients of OH with CH 3 OH and CH 2 (OH) 2 are similar [107, 109].…”

“…Other than the gaseous phenomena, ssFTIR has been extensively used to monitor the time-resolved infrared difference spectra of a given system in condensed phase upon various stimuli, such as the reorientation dynamics of liquid crystals upon electric perturbation [37,38], the molecular reorientation of a polymer upon mechanical stretching [39], and a rich variety of light-induced processes, such as photocycles of the various retinal proteins [40][41][42][43][44][45][46][47][48], the photolysis and excited-state properties of metal complexes [49][50][51][52][53][54][55][56], the photodissociation of small molecule [57], aqueous chemical reactions [58,59], the displacement dynamics of self-assembled molecules [60], and the exciplex dynamics of thermally activated delayed fluorescence (TADF) organic light emitting diodes [61]. In addition to the absorption mode, my research team has recently employed ssFTIR to probe the transient infrared thermal emission of gold nanostructures upon photoexcitation to characterize the thermalization in various nanostructures [62][63][64][65].…”