Akagi Hiroshi, Fukazawa Hiroshi, Yokoyama Keiichi, Yokoyama Atsushi
Department of Materials Science, Japan Atomic Energy Research Institute, Tokai-mura, Naka-gun, Ibaraki 319-1195, Japan.
J Chem Phys. 2005 Nov 8;123(18):184305. doi: 10.1063/1.2104532.
Exclusively selective OD bond dissociation of HOD has been demonstrated by the ultraviolet photodissociation at 243.1 nm through the fourth overtone state of the OD stretching mode (5nu(OD)). Branching ratio between the OH and OD bond dissociation channels has been determined by detecting H and D atoms, utilizing a (2+1) resonance-enhanced multiphoton ionization (REMPI) process. The OD bond dissociation has been solely observed with the branching ratio phi(D+OH)/phi(H+OD)>12, which has been determined by the detection limit for the H atom. Time-dependent wave-packet calculations reveal two important features for the highly selective OD bond dissociation: (1) strong local-mode character of the 5nu(OD) state and (2) limitation of the total excitation energy lower than the saddle point between the OH and OD dissociation channels in the A state. Additionally, the recoil velocity and angular distribution of the nascent D atom are roughly evaluated by analyzing the Doppler-resolved REMPI spectrum. Based on these results, the dynamics of the selective OD dissociation has been discussed in detail.
通过243.1 nm的紫外光解离，利用OD伸缩模式（5ν(OD)）的第四泛音态，已证明了HOD的唯一选择性OD键解离。通过利用(2+1)共振增强多光子电离（REMPI）过程检测H和D原子，确定了OH和OD键解离通道之间的分支比。仅观察到OD键解离，其分支比φ(D+OH)/φ(H+OD)>12，这是由H原子的检测限确定的。含时波包计算揭示了高选择性OD键解离的两个重要特征：（1）5ν(OD)态的强局域模特征；（2）总激发能低于A态中OH和OD解离通道之间鞍点的限制。此外，通过分析多普勒分辨的REMPI光谱，大致评估了新生D原子的反冲速度和角分布。基于这些结果，详细讨论了选择性OD解离的动力学。
