Knowledge Bank

By reversing the focus of attention from the solute to the matrix, the standard matrix isolation technique developed and exploited extensively by Pimentel, and his students, can be modified so that it is readily applicable to studies of unstable intermediates or unusual products in organic and inorganic reactions with relatively high reaction activation energies. In this modified technique, which we shall call for convenience inverse matrix isolation spectroscopy, a solute either stable or unstable is trapped in a chemically reactive matrix and then reactions between the solute and matrix are initiated by warming the sample. The spectrum of the matrix is studied in detail as the extent of reaction increases, and absorption bands of the reaction intermediates and products are identified. Generally the samples can be fractionated to reduce the matrix while leaving the intermediates or products unchanged. Examples from such studies at liquid nitrogen temperature with $NH3,CO2,H2C=CHCl,CH3CH=CH2$, and $H2C=CHCH=CH2$ as matrices and $H2O,SO2,O3$ and atomic metals Ni and Mg as solutes will be described.