利用离子速度影像技术结合共振增强多光子电离(REMPI)技术,研究了邻溴甲苯在234和267 nm激光作用下的光解机理.平动能分布表明,基态Br(2P3/2和自旋轨道激发态Br(2>P3/2)产生于两个解离通道:快通道和慢通道.快通道的各向异性参数在234 nm分别为1.15(Br)和0.55(Br*),在267nm分别为0.90(Br)和0.60(Br*).慢通道的各向异性参数在234nm分别为0.12(Br)和0.14(Br*),在267nm分别为0.11(Br)和0.10(Br*).源自于慢通道的Br和Br*碎片的各向异性弱于快通道.Br(2P3/2)的相对量子产率φ(Br)在234 nm为0.67,在267 nm为0.70.邻溴甲苯在234和267 nm光解主要产生基态产物Br(2P3/2).快通道产生于(π,π*)束缚单重态被激发,随后通过排斥性(n,σ)态的预解离.慢通道各向异性参数接近零,由此证实慢通道来源于单重激发态内转换到高振动基态而引发的热解离.%The photedissociation of o-bromotoluene was studied at 234 and 267 nm using velocity map imaging combined with a resonance-enhanced multiphoton ionization (REMPI) technique. Translational energy distributions suggested that ground state Br(2P3/2) and spin-orbit excited state Br*(2P3/2) fragments were all generated via two dissociation channels: a fast channel and a slow channel. The anisotropy parameters of the fast channels were determined to be 1.15 (Br) and 0.55 (Br*) at 234 am, 0.90 (Br) and 0.60 (Br*) at 267 am. The anisotropy parameters of the slow channels were 0.12 (Br) and 0.14 (Br*) at 234 am, 0.11 (Br) and 0.10 (Br*) at 267 am. The Br and Br* fragments of the slow channel were less anisotropic than those of the fast channel. The total relative quantum yields of Br (φ(Br)) were 0.67 at 234 nm and 0.70 at 267 run. Ground state Br(2P,3/2) was the main product from the photolysis of o-bromotoluene at 234 and 267 am. We propose that the fast channel originates from excitation of bound excited singlet (π,π*)states followed bypredissociation along repulsive (n,σ*) states. The anisotropy parameters of the slow channels were close to zero indicating a hot dissociation mechanism on a highly vibrational ground state followed the internal conversion of the excited singlet state.
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