2002 Fiscal Year Final Research Report Summary
Structures and Reactivities of Negatively-Charged Clusters in Supercritical Carbon Dioxide
| Project/Area Number |
12440160
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Physical chemistry
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| Research Institution | The University of Tokyo |
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Principal Investigator |
NAGATA Takashi The University of Tokyo, Graduate School of Arts and Sciences, Professor, 大学院・総合文化研究科, 教授 (10164211)
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| Co-Investigator(Kenkyū-buntansha) |
ITOH Kengo The University of Tokyo, Graduate School of Arts and Sciences, Research assistant, 大学院・総合文化研究科, 助手 (40221080)
WATANABE Kazuo The University of Tokyo, Graduate School of Arts and Sciences, Research assistant, 大学院・総合文化研究科, 助手 (90312206)
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| Project Period (FY) |
2000 – 2002
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| Keywords | Supercritical carbon dioxide / Mobility measurement / Negatively-charged clusters / Ab initio calculations / Photodestruction spectrum / Radical reactions / Negative-ion chemistry |
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| Research Abstract |
The present study aims for (i) the spectroscopic detection of (CO_2)_n^-clusters formed in a supercritical carbon dioxide (hereafter referred to as {(CO_2)_n^-}_<scf>) and (ii) the systematic study of reactivities of {(CO_2)_n^-}_<scf> in order to explore the negative-ion chemistry in supercritical carbon dioxide. The findings are summarized as follows :
1.The formation of {(CO_2)_n^-}_<scf> is detected by the measurement of negative charge transport in gaseous, supercritical and liquid carbon dioxide. The mobility measurement over a wide range of CO_2 density revealed that the nascent {(CO_2)_n^-}_<scf> formed around the excess electrons are primarily in the size range of n = 5 -6, and that the negative charge transport occurs with both the hopping and the conduction band mechanisms.
2.The electronic and geometrical structures of (CO_2)_n^-and [(CO_2)_n^-(H_2O)_m] are investigated by ab initio calculations at MP2/6-311++G(d, p) level for small clusters and MP2/6-31 for larger ones, demo
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nstrating the existence of almost-isoenergetic isomers having different electronic structures ("electronic isomers").
3.An effort has been made to probe the nascent {(CO_2)_n^-}_<scf> formed in a supercritical pure carbon dioxide by ns time-resolved photoabsorption spectroscopy. The transient photoabsorption signal has not been detected due possibly to either small quantum yield for the {(CO_2)_n^-}_<scf> formation or small cross sections for the {(CO_2)_n^-} photoabsorption.
4.The photodestruction spectra of (CO_2)_n^-are measured in the visible and uv regions by means of photofragment mass spectrometry, which provide information on the fundamental electronic properties of (CO_2)_n^-species.
5.Mass spectrometric studies have revealed the reactivity of gas-phase (CO_2)_n^-and CO_2^-(H_2O)_n as carboxylation reagents for alkyl halides and conjugated alkenes. The hydration stabilizes CO_2^<・-> without deteriorating its radical reactivity. These findings open up a possibility of novel {(CO_2)_n^-}_<scf> chemistry in a supercritical carbon dioxide. Less
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