Halogen Effect on the Photodissociation Mechanism for Gas‐Phase Bromobenzene and Iodobenzene |
| |
Authors: | Xiao‐Peng Zhang Zheng‐Rong Wei Ying Tang Ting‐Jung Chao Bing Zhang King‐Chuen Lin |
| |
Institution: | 1. Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 106, Taiwan, Fax: (+886)?2‐23621483;2. Department of Chemistry, National Taiwan University, Taipei 106, Taiwan;3. State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071, P. R. China;4. Current address: Chemical Dynamics Lab., RIKEN, Wako 351‐0198, Japan |
| |
Abstract: | The velocity imaging technique combined with (2+1) resonance‐enhanced multiphoton ionization (REMPI) is used to detect the halogen fragments in the photodissociation of bromobenzene and iodobenzene at 266 nm. With the aid of potential energy curve calculations by Lunell (Y. J. Liu, P. Persson, S. Lunell, J. Phys. Chem. A 2004 , 108, 2339–2345.), the Br fragmentation is proposed to stem from excitation of the lowest excited singlet state followed by predissociation along a repulsive triplet state. The slowed dissociation rate leads to production of the isotropic Br fragments and 93 % internal energy deposition. Only the ground state Br(2P3/2) is detectable. In contrast, when iodine is substituted, the iodine effect stabilizes the repulsive states associated with the I? C6H5 bond rupture and the subsequent dissociation channels become more complicated. 84 % of the iodobenzene molecules obtained follow a direct dissociation channel, while the remaining undergo a predissociative process. Both routes result in rapid dissociation with anisotropy parameters of 0.7±0.2 and 0.9±0.2 as well as 70 % and 26 % in the fractions of translational energy deposition, respectively. The relative quantum yields of I* and I are 0.35 and 0.65 and their related photodissociation pathways are discussed in detail. |
| |
Keywords: | halogens photochemistry resonance‐enhanced multiphoton ionization reactive intermediates velocity imaging |
|
|