环戊烯臭氧化反应瞬变物种产生机制

大气中烯烃臭氧化反应产物是二次有机气溶胶(SOA)形成的重要前体物. 运用自行组建的低温基质隔离系统研究环戊烯臭氧化反应的瞬变物种产生机制. 采用程序升温方法,将温度从6 K升至115 K,用傅里叶红外光谱仪检测不同温度下生成的活性中间体,并将试验值与理论计算值、文献报道值进行对比,以确定中间体构型. 结果表明:环戊烯臭氧化反应生成的中间体——POZ(初级臭氧化物)、SOZ(二次臭氧化物)和CI(一分子羰基氧化物和一分子醛或酮)被成功检测到. 其中,POZ的特征吸收峰在705和946 cm-1处,对应O—O—O反对称伸缩振动和环变形振动；SOZ特征吸收峰在939 cm-1处,对应C—O伸缩振动；CI的特征吸收峰在1 733和853 cm-1处,分别对应CO伸缩振动和O—O伸缩振动. 据此,环戊烯臭氧化反应遵循Criegee机制. 采用4种量子化学计算方法——B3LYP/6-311++G(d,2p)、B3LYP/6-311++G(3df,3pd)、MP2/aug-cc-pvdz和PW91PW91/6-311++G(3df,3pd),计算POZ、SOZ和CI特征吸收峰的振动频率,其中POZ在705 cm-1处吸收峰的振动频率计算值分别为725、698、703、680 cm-1；SOZ在1 030 cm-1处吸收峰的振动频率计算值分别为1 017、1 018、1 025和993 cm-1；CI在1 733 cm-1处吸收峰的振动频率计算值分别为1 796、1 803、1 732和1 745 cm-1.表明MP2/aug-cc-pvdz计算的特征振动频率与试验值最接近. 

Theoretical and Experimental Study of the Formation Mechanism of Transient Species in the Ozonolysis of Cyclopentene

Alkene ozonolysis products are precursors of secondary organic aerosol (SOA) formation. In the present study, the formation of transient species in the ozonolysis of cyclopentene was investigated using the self-established system of matrix isolation in the condensed phase at temperatures ranging from 6 K to 115 K. In the experiment, the reactive intermediates were monitored using MI-FTIR during heating-up, and band assignment and structure identification were confirmed, combined with theoretical calculations and reported literature. The experimental results showed that POZ, SOZ and CI intermediates were successfully detected. The characteristic peaks of POZ at 705 and 946 cm-1 were assigned to O—O—O asymmetric stretching and ring deformation, respectively. While the characteristic peak of SOZ at 939 cm-1 was assigned to C—O stretching, those of CI, at 1733 and 853 cm-1, were assigned to CO stretching and O—O stretching, respectively. The results effectively supported the Criegee mechanism of the cyclopentene ozonolysis. The computed vibrational frequencies with four methods of B3LYP/6-311++G(d,2p), B3LYP/6-311++G(3df,3pd), MP2/aug-cc-pvdz and PW91PW91/6-311++G(3df,3pd) were compared with the experimental values. The measured value of POZ absorption peak was at 705 cm-1, and the results of four computational methods were at 725,8, 703 and 680 cm-1 respectively. The measured value of SOZ absorption peak was at 1030 cm-1, and the results of four computational methods were at 1017,8, 1025 and 993 cm-1. Also, the measured value of CI absorption peak was at 1733 cm-1, and the results of four computational methods were at 1796,3, 1732 and 1745 cm-1. The ab initio MP2/aug-cc-pvdz method showed very good performance in predicting characteristic vibrations and agreed well with the experimental data.