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Photodissociation Branching Ratios of 12C16O from 108000 cm-1 to 113200 cm-1 Measured by Two-Color VUV-VUV Laser Pump-Probe Time-Slice Velocity-Map Ion Imaging Method: Observation of Channels for Producing O(1D)
Hong Gao*1,2, Yu Song2, William M. Jackson2, Cheuk-Yiu Ng2
1.Beijing National Laboratory for Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China;2.Department of Chemistry, University of California, Davis CA 95616, USA
Abstract:
The photoabsorption and photodissociation of carbon monoxide (CO) in the vacuum ultraviolet (VUV) region is one of the most important photochemical processes in the interstellar medium, thus it has attracted numerous experimental and theoretical studies. Here, we employed the two-color VUV-VUV laser pump-probe time-slice velocity-map ion imaging method to measure the relative branching ratios [C(3P0)+O(1D)]/{[C(3P0)+O(3P)]+[C(3P0)+O(1D)]} and [C(3P2)+O(1D)]/{[C(3P2)+O(3P)]+[C(3P2)+O(1D)]} in the VUV photoexcitation energy range of 108000-113200 cm?1. Here, one tunable VUV laser beam is used to excite CO to specific rovibronic states, and a second independently tunable VUV laser beam is used to state-selectively ionize C(3P0) and C(3P2) for detection. State-selective photoionization through the 1VUV+1UV/visible resonance-enhanced multiphoton ionization scheme has greatly enhanced the detection sensitivity, which makes many new weak absorption bands observable in the current study. The branching ratio measurement shows that the spin-forbidden channels C(3P0)+O(1D) and C(3P2)+O(1D) only open at several discrete narrow energy windows. This might be caused by certain accidental resonance- enhanced spin-orbit interactions between the directly excited Rydberg states and valence states of triplet type which finally dissociate into the spin-forbidden channels.
Key words:  Carbon monoxide, Photodissociation, Vacuum ultraviolet, Branching ratio
FundProject:
用两束真空紫外激光和离子速度成像方法测量12C16O分子在108000∽113200 cm-1能量范围的解离通道分支比:生成O(1D)通道的观测
高 蕻*1,2, 宋 煜2, William M. Jackson2, 伍灼耀2
1.中国科学院化学研究所,北京分子科学国家研究中心,北京 100190;2.加利福尼亚大学戴维斯分校化学系,戴维斯 95616
摘要:
本文利用两束可调谐真空紫外激光和离子速度成像的方法测量了CO在108000∽113200 cm-1光解离通道分支比[C(3P0)+O(1D)]/{[C(3P0)+O(3P)]+[C(3P0)+O(1D)]}和[C(3P2)+O(1D)]/{[C(3P2)+O(3P)]+[C(3P2)+O(1D)]}. 本文先用一束真空紫外激光将CO分子激发至特定的高激发量子态并发生解离,接着用另一束真空外激光选择性地电离C(3P0)和C(3P2)并进行探测. 1VUV+1UV/visible共振增强多光子电离的方法大大提高了实验的探测灵敏度,使得之前没有观测到的较弱的吸收带也首次被观测到. 通过分支比的测量,发现自旋禁阻的解离通道C(3P0)+O(1D)和C(3P2)+O(1D) 只在某些分立的较窄能量范围内才能被观测到. 这可能是由于直接激发的高里德堡态和解离到上述自旋禁阻通道的价态在这些能量范围内发生了共振的自旋-轨道耦合相互作用.
关键词:  一氧化碳,真空紫外,光解离,通道分支比,离子速度成像
DOI:10.1063/1674-0068/cjcp1911199
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