Control of chemical reactions = 화학 반응의 제어

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The photodissociation dynamics of $CH_2BrCl$ has been studied at 234 nm utilizing the molecular beam-imaging system. In the photolysis, the C-Br bond fission is observed exclusively. The internal energy of the Br($^2P_{3/2}$) channel consists of two parts which is caused by the interaction between $σ^*$(C-Br) and $σ^*$(C-Cl) surfaces. This separation is newly resolved and studied to unravel the effect of chromophore. The energy separation of two peaks is $25 kJ mol^{-1}$ and the ratio of the fast to slow one is 3.2. The fast part is interpreted in terms of a rigid impulsive model with no vibrational excitation and the slow part by a soft with a little vibrational excitation, respectively. The energy gap is suggested to be due to an umbrella motion. The dissociation dynamics of $CF_2ClBr$ at 234nm is studied using a state-selected photofragment imaging technique. Two primary dissociation channels, $CF_2Cl + Br$ and $CF_2Br + Cl$, are observed with the relative yields of 0.96 and 0.04. The energy partitionings of photofragments for these channels are explained in terms of the rigid and soft radical impulsive models, respectively. For the $CF_2Cl + Br$ channel, the branching ratio of Br($^2P_{1/2}$) and Br($^2P_{3/2}$) is determined to be 0.41±0.05 and the anisotropy parameters are found to be β=1.60±0.1 for Br($^2P_{1/2}$) and β=1.05±0.1 for Br($^2P_{3/2}$). It is proposed that the $CF_2Br + Cl$ process is due to intramolecular energy transfer from the C-Br bond. A study has been performed to achieve bond-selective photodissociation/photoionzation of $CH_2BrCl$ in the gas phase by employing an adaptive femtosecond laser pulse shaping technique. The photoproduct signal measured in a reflectron time-of-flight mass spectrometer is used as feedback to improve iteratively the spectral phases of the laser pulse via an evolutionary algorithm. We observe an increase of the branching ratio, 1:6 of the stronger versus the weaker carbon halogen bond by 100% in comparison...
Lee, Eok-KyunresearcherJung, Kyung-Hoonresearcher이억균researcher
한국과학기술원 : 화학과,
Issue Date
177233/325007 / 000995273

학위논문(박사) - 한국과학기술원 : 화학과, 2002.8, [ viii, 84 p ]


laser; feedback; dynamics; coherent control; evolutionary algorithm; 제어; 화학반응; 레이저; 피드백; 동력학

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