Chemistry in low-temperature matrices

Abstract

This is the fifth report in this series on Matrix Isolation; the previous reports appeared in the 1985, 1991, 1997 and 2001 volumes of Annual Reports on the Progress of Chemistry, Section C. The report is divided into sections: weak adducts and conformational isomers; reactions of atoms; high-temperature molecules; photochemistry; biological molecules; astrochemistry. The last two sections reflect the fact that matrix isolation now extends into areas outside the traditional mainstream disciplines of chemistry. There are a number of areas where substantial progress has been made during the period of this report. First, the routine use of laser-ablation to generate atoms and to initiate atomic reactions in matrices has increased the scope of matrix isolation to synthesise many new molecular species in inorganic chemistry. Laser-ablation allows ground state atoms to be more easily studied than is the case when atoms are produced by thermal methods. Moreover, this procedure allows atoms to be generated from materials where thermal production is difficult. Secondly, the manufacture of more efficient closed-cycle helium refrigerators allows hydrogen matrices to be deposited readily. A significant body of work therefore has focussed upon metal hydrides, dihydrogen complexes and other hydrogen species in matrices. Underpinning all of this experimental work are theoretical calculations, without which the correct identification of most matrix isolation molecules would remain dangerously ambiguous. Infrared spectroscopy remains—as it has for the past 50 years—the workhorse of matrix isolation studies. It does seem that this situation will not change—it is impossible to conceive of another spectroscopic method that combines the necessary sensitivity to study molecules at very low dilution with the structural information required to make a reasonably certain identification.