期刊
JOURNAL OF CHEMICAL PHYSICS
卷 147, 期 1, 页码 -出版社
AMER INST PHYSICS
DOI: 10.1063/1.4981025
关键词
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资金
- Ministry of Science and Technology, Taiwan [NSC 102-2113-M-002-009-MY3]
- Italian Ministry for Education, University and Research, MIUR through SIR [RBSI14U3VF]
- Grants-in-Aid for Scientific Research [17KT0008] Funding Source: KAKEN
The asymmetric-top molecule 2-bromobutane is oriented by means of a hexapole state selector; the angular distribution of the bromine atom photofragment, for the two fine-structure components, is acquired by velocity-map ion imaging. The molecular beam, spatially oriented along the time-of-flight axis, is intersected with a linearly polarized laser, whose polarization is tilted by 45 degrees with respect to the detector surface. To obtain the mixing ratio of the perpendicular and parallel transitions, the fragment ion images and angular distributions can be appropriately simulated to give insight on the population mechanism of the specific electronic state involved at each selected excitation wavelength. The photofragment images obtained at 238.6 nm yielded an asymmetry factor beta(1) of 0.67, indicative of the extent of molecular orientation, and an anisotropy parameter beta(2) of 1.03, which is a signature of a prevailing parallel transition along the C-Br axis. When the photolysis wavelength is tuned to 254.1 nm, the corresponding angular distribution is less asymmetric (beta(1) = 0.24) and the obtained small value beta(2) = 0.12 is a characteristic of a predominantly perpendicular transition. The photofragment angular distributions are also affected by hexapole voltage, especially regarding the asymmetry factor, and this aspect provides information on the effect of molecular orientation. Published by AIP Publishing.
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