Structures and Reactivities of Negatively-Charged Clusters in Supercritical Carbon Dioxide

点击翻译按钮获取中文摘要

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 … More 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