Cage effect, matrix isolation

Matrix isolation has many limitations, even for metal carbonyls (i) it cannot easily be used for charged species2 (ii) very little kinetic information can be obtained because of the restricted temperature range and limited diffusion (iii) the solid matrix cage can effectively block some... 

The cage effect can be a source of great frustration in matrix isolation studies of monoradicals, because such species are usually formed by homolysis from closed-shell compounds, and hence any radical generated in situ is invariably accompanied by another radical that will be trapped in the same matrix cage. 

K, and, in this way, the analytes are frozen into a cage of argon molecules, i.e., matrix-isolated. The diameter of the spots is a little larger than that obtained with the DD technique, i.e., 200-300 p,m. Matrix-isolated spectra maydiffer from spectra that have been recorded with conventional methods. In particular, relatively small molecules (MW < 200) may exhibit considerable band-narrowing effects. As a consequence, identification of GC/ MI-FTIR spectra demands special reference collections. 

Theoretical analyses (75-77) of the matrix-induced changes in the optical spectra of isolated, noble-metal atoms have also been made. The spectra were studied in Ar, Kr, and Xe, and showed a pronounced, reversible-energy shift of the peaks with temperature. The authors discussed the matrix influence in terms of level shift-differences, as well as spin-orbit coupling and crystal-field effects. They concluded that an increase in the matrix temperature enhances the electronic perturbation of the entrapped atom, in contrast to earlier prejudices that the temperature dilation of the surrounding cage moves the properties of the atomic guest towards those of the free atom. 

Discussion. Copper in Krypton. The absorption spectra of copper atoms Isolated in rare gas matrices have been extensively studied (15-25) and the triplet of bands at 310nm attributed to a number of different causes. These include (1) spin orbit splitting and static axial site distortion (17), (2) multiple matrix sites (18), (3) exciplex formation between the metal and a single matrix atom (19), (4) long range metal-metal interactions (2 ), and (5) Jahn-Teller (JT) effect resulting from matrix cage atom vibrations on the excited metal (21,22,23). The MCD of Cu atoms in the rare gas matrices has recently been reported (24,25) and the results interpreted as consistent with either the distorted site or JT hypotheses (39). 

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