大气环境中Br自由基与HONO分子反应机理的理论研究

Theoretical study on the reaction mechanism of atomic radical Br with nitrous acid HONO in atmosphere

用非限制性二阶微扰理论研究了大气环境中Br自由基与亚硝酸分子反应的机理.在6-311++G**和6-311G**基组水平上,优化得到了反应途径上反应物、过渡态、中间体和产物的几何构型;在UMP2/6-311++G**优化的构型基础上,利用CCSD(T)/aug-cc-pVTZ方法得到各驻点的高级单点能量;通过振动分析对过渡态和中间体构型进行了确认.计算结果表明,Br自由基与HONO的反应有4种反应机制,第1种是通过过渡态TSC1-P1和TSC3-P1生成产物P1的直接H提取机制.第2种是Br自由基加成到HONO分子羟基O原子上消去NO的加成-消除机制.第3种是Br自由基进攻HONO分子N原子生成产物P3.第4种是Br自由基对HONO分子末端O的进攻.其中生成产物P1的反应途径R→C3→TSC3-P1→P1是主反应通道,并且反式HONO分子的反应竞争性更强.

The mechanism of atomic radical Br with nitrous acid HONO in atmosphere was investigated with the unrestricted MФller-Plesset perturbation theory.The geometrical parameters for the involved stationary points on the potential energy surface were calculated using the 6-311＋＋G＊ ＊ and 6-311 G＊ ＊basis set,respectively.The UMP2/6-311＋＋G（d,p） optimized geometries were used for the single-point coupled cluster calculations without reoptimization at the CCSD（T）/aug-cc-pVTZ level,and the intermediates and transition states were detected by the frequency analysis.The calculation results show that the Br＋HONO reaction has four different mechanisms.The first mechanism involves hydrogen picked-up by atomic radical Br,via surmounting TSC1-P1 and TSC3-P1 leading to product P1 NO2 ＋ HBr.The second mechanism involves atomic radical Br addition to the hydroxyl-oxygen of HONO,followed by the elimination of NO.The third mechanism occurs by atomic radical Br kissing the N-atom of HONO to give product P3.The fourth mechanism features atomic radical Br addition to the terminal O-atom of HONO.The dominant reaction channel is the reaction pathway R→C3→TSC3-P1→P1 and consequently the major product is P1 NO2 ＋HBr,and the trans-HONO isomer is apparently more reactive.