The aminomethyl (•CH 2 NH 2 ) radical is generated from the photo-oxidation of methylamine in the troposphere and is an important precursor for new particle formation. The effect of ammonia and water on the gas-phase formation of methanimine (CH 2 NH) from the • CH 2 NH 2 + O 2 reaction is not known. Therefore, in this study, the potential energy surfaces for • CH 2 NH 2 + O 2 (+NH 3 /H 2 O) were constructed using ab initio //DFT, i.e., coupled - cluster theory (CCSD(T))//hybrid-density functional theory, i.e., M06-2X with the 6-311++G (3df, 3pd) basis set. The Rice-Ramsperger-Kassel-Marcus (RRKM)/master equation (ME) simulation with Eckart's asymmetric tunneling was used to calculate the rate coefficients and branching fractions relevant to the troposphere. The results show 40% formation of CH 2 NH at the low-pressure (<1 bar) and 100% formation of CH 2 NH 2 OO • at the high-pressure limit (HPL) condition. When an ammonia molecule is introduced into the reaction, there is a slight increase in the formation of CH 2 NH; however, when a water molecule is introduced into the reaction, the increase in the formation of CH 2 NH was from 40% to ∼80%. The calculated rate coefficient for • CH 2 NH 2 + O 2 (+NH 3 ) [1.9 × 10 -23 cm 3 molecule -1 s -1 ] and for CH 2 NH 2 + O 2 (+H 2 O) [3.3 × 10 -17 cm 3 molecule -1 s -1 ] is at least twelve and six order magnitudes smaller than those for free • CH 2 NH 2 + O 2 (2 × 10 -11 cm 3 molecule -1 s -1 at 298 K) reactions, respectively. Our result is consistent with that of previous experimental and theoretical analysis and in good agreement with its isoelectronic analogous reaction. The work also provides a clear understanding of the formation of tropospheric carcinogenic compounds, i.e., hydrogen cyanide (HCN).
Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
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