Theoretical Study On The Reaction Of Criegee Intermediate RCHOO (R=H, CH 3 /CH 3 CH 2 ) With NCO And (H 2 O) N (n=1-3)

Criegee intermediates are carbonyl oxides formed in the ozonolysis of unsaturated hydrocarbons,In the atmosphere,Criegee intermediates undergo bimolecular reactions with atmospheric molecules and unimolecular isomerization and decomposition to yield OH,their atmospheric fate plays a critical role in determining secondary organic aerosol formation.Because of there are many types of Criegee intermediate,the reactivity of different substituent and conformation are different.we report a theoretical study on different Criegee intermediate RCHOO(R=H,CH3,and CH3CH2),The work mainly includes tow parts as follows:Part one:A comprehensive theoretical study about the reaction of RCHOO(R=H,CH3)with NCO is performed at the CCSD(T)/aug-cc-pVTZ//B3LYP/6-311+G(2df,2p)leveL The rate coefficients for the dominant reaction channels are determined at 298-500 K using conventional transition state theory(TST)with a Eckart tunneling.The result shows that the detailed mechanism mainly includes addition,oxidation and hydrogen abstraction reactions.N and O atoms of the NCO radical can react to RCHOO(R=H and CH3)in each reaction mode.Moreover,the end O atom of NCO addition to RCHOO(R-H and CH3)a-C is favored for the addition reaction,while the reactions involving the end N atom of NCO is advantaged in both oxidation and hydrogen abstraction The methyl substituents in the CH2OO produce an increase of the reactivity.anti-CH3CHOO shows a higher reactivity than syn-CH3CHOO towards addition and oxidation reaction,but for the hydrogen abstraction,syn-CH3CHOO is significantly more reactive than anti-CH3CHOO.Part two:A comprehensive theoretical study about the reaction of CH3CH2CHOO with(H20)n(n==1-3)is performed at the CCSD(T)//B3LYP/6-311+G(2df,2p)leveL The result shows that syn-CH3CH2CHOO is more favorable than anti-CH3CH2CHOO by about 13.75 kJ· morl,and the transformation of anti-CH3CH2CHOO to syn-CH3CH2CHOO has a 172.28 kJ·mor1 energy barrier.In addition,The two conformers rotate about the central C-C bond,changing the position of the terminal methyl group,there have another two conformers sd-CH3CH2CHOO and ad-CH3CH2CHOO,the rotational energy barrier are10.42 and 5.20 kJ·mol-1 respectively.In the reaction of CH3CH2CHOO with(H2O)n,the detailed mechanism mainly includes addition-coupled hydrogenatom transfer and hydrogen transfer reactions and the addition-coupled hydrogenatom transfer is advantaged.At 298K,the rate constant of anti-/ad-/synr/sd-CH3CH2CHOO+H2O are 1.64× 1 0-15/5.24× 10-16/4.49x 1 0-19/7.20× 10-20m3·molecule-1·s-1 respectively.Furthermore,the rate constant of anti-/ad-CH3CH2CHOO with temperature change is very slow,the syn-/sd-CH3CH2CHOO obey a significant positive temperature effect.In the reaction of CH3CH2CHOO with(H2O)n(n=2,3),the contribution of apparent activation energy is significantly increased with the increase in the number of water molecules involved and the rate constant of satisfies a strong negative temperature dependent.