Department of Chemistry, University of California, Berkeley, California 94720, USA and Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
J Chem Phys. 2018 Jan 28;148(4):044309. doi: 10.1063/1.5011985.
The photodissociation dynamics of the simplest alkyl peroxy radicals, methyl peroxy (CHOO) and ethyl peroxy (CHOO), are investigated using fast beam photofragment translational spectroscopy. A fast beam of CHOO or CHOO anions is photodetached to generate neutral radicals that are subsequently dissociated using 248 nm photons. The coincident detection of the photofragment positions and arrival times allows for the determination of mass, translational energy, and angular distributions for both two-body and three-body dissociation events. CHOO exhibits repulsive O loss resulting in the formation of O(D) + CHO with high translational energy release. Minor two-body channels leading to OH + CHO and CHO + O(P) formation are also detected. In addition, small amounts of H + O(P) + CHO are observed and attributed to O loss followed by CHO dissociation. CHOO exhibits more complex dissociation dynamics, in which O loss and OH loss occur in roughly equivalent amounts with O(D) formed as the dominant O atom electronic state via dissociation on a repulsive surface. Minor two-body channels leading to the formation of O + CH and HO + CH are also observed and attributed to a ground state dissociation pathway following internal conversion. Additionally, CHOO dissociation yields a three-body product channel, CH + O(P) + CHO, for which the proposed mechanism is repulsive O loss followed by the dissociation of CHO over a barrier. These results are compared to a recent study of tert-butyl peroxy (t-BuOO) in which 248 nm excitation results in three-body dissociation and ground state two-body dissociation but no O(D) production.
最简单的烷基过氧自由基，甲基过氧（CHOO）和乙基过氧（CHOO）的光解动力学，是使用快束光电子碎片平动光谱学来研究的。一束快速的 CHOO 或 CHOO 阴离子被光解，生成中性自由基，随后用 248nm 光子使其解离。光碎片位置和到达时间的同时检测，允许确定两种和三种离解事件的质量、平动能和角分布。CHOO 表现出排斥性的 O 损失，导致 O(D) + CHO 的形成，并伴随着高平动能释放。还检测到少量导致 OH + CHO 和 CHO + O(P)形成的两个体通道。此外，观察到少量的 H + O(P) + CHO，并归因于 O 损失后 CHO 的解离。CHOO 表现出更复杂的离解动力学，其中 O 损失和 OH 损失发生的数量大致相等，O(D) 通过在排斥表面上的离解形成主要的 O 原子电子态。还观察到少量导致 O + CH 和 HO + CH 形成的两个体通道，并归因于内部转化后的基态离解途径。此外，CHOO 离解产生 CH + O(P) + CHO 的三体产物通道，提出的机制是排斥性的 O 损失，随后是 CHO 越过势垒的解离。这些结果与最近对叔丁基过氧（t-BuOO）的研究进行了比较，在该研究中，248nm 激发导致三体离解和基态两个体离解，但没有 O(D)生成。
