AUTHOR=Nulakani Naga Venkateswara Rao , Ali Mohamad Akbar TITLE=Unveiling the chemical kinetics of aminomethanol (NH2CH2OH): insights into O.H and O2 photo-oxidation reactions and formamide dominance JOURNAL=Frontiers in Chemistry VOLUME=12 YEAR=2024 URL=https://www.frontiersin.org/journals/chemistry/articles/10.3389/fchem.2024.1407355 DOI=10.3389/fchem.2024.1407355 ISSN=2296-2646 ABSTRACT=

Aminomethanol is released into the atmosphere through various sources, including biomass burning. In this study, we have expounded the chemical kinetics of aminomethanol in the reaction pathways initiated by the hydroxyl radical (O˙H) with the aid of ab initio//density functional theory (DFT) i.e., coupled-cluster theory (CCSD(T))//hybrid-DFT (M06-2X/6-311++G (3df, 3pd). We have explored various possible directions of the O˙H radical on aminomethanol, as well as the formation of distinct pre-reactive complexes. Our computational findings reveal that the H transfer necessitates activation energies ranging from 4.1 to 6.5 kcal/mol from the –CH₂ group, 3.5–6.5 kcal/mol from the –NH₂ group and 7–9.3 kcal/mol from the –OH group of three rotational conformers. The H transfer from –CH₂, –NH₂ and –OH exhibits an estimated total rate constant (k_OH) of approximately 1.97 × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ at 300 K. The branching fraction analysis indicates a pronounced dominance of C-centered NH₂C˙HOH radicals with a favorability of 77%, surpassing the N-centered N˙ HCH₂OH (20%) and O-centered NH₂CH₂O˙ (3%) radicals. Moreover, our investigation delves into the oxidation of the prominently favored carbon-centered NH₂C˙HOH radical through its interaction with atmospheric oxygen molecules. Intriguingly, our findings reveal that formamide (NH₂CHO) emerges as the predominant product in the NH₂C˙HOH + ³O₂ reaction, eclipsing alternative outcomes such as amino formic acid (NH₂COOH) and formimidic acid (HN = C(H)-OH). At atmospheric conditions pertinent to the troposphere, the branching fraction value for the formation of formamide is about 99%, coupled with a rate constant of 5.5 × 10⁻¹² cm³ molecule⁻¹ s⁻¹. Finally, we have scrutinized the detrimental impact of formamide on the atmosphere. Interaction of formamide with atmospheric hydroxyl radicals could give rise to the production of potentially perilous compounds such as HNCO. Further, unreacted N˙HCH₂OH radicals may initiate the formation of carcinogenic nitrosamines when reacting with trace N-oxides (namely, NO and NO₂). This, in turn, escalates the environmental risk factors.