IR-active matrix-isolated molecules (CO and CO2) to probe host crystal (N-2) quality

The matrix isolation technique is a powerful technique for specific questio ns. But due to relatively high impurity concentrations (10(-2)-10(-4)) the impurity is not in a real matrix-isolated case, as in theoretical descripti ons. In addition, due to sample preparation (cold deposition) the matrix re sembles more an amorphous thin film rather than a good crystal, in terms of solid state physics. As a consequence, many spectroscopic data or phenomen a were misinterpreted in the past. Therefore, we studied the real matrix-is olated case (similar to 10(-7)) in pretty good bulk matrix material. Lookin g at impurity spectra (CO, CO2, and their isotopes) and analyzing bandwidth s, frequencies, and intensities as a function of temperature, we could char acterize the quality of structural phase transitions of matrix and its hyst eresis; we could unambiguously assign crystal field splitting to orientatio ns of matrix-isolated particles in the host crystal; we could separate homo geneous from inhomogeneous bandwidth and discuss crystal quality of matrix; due to carefully determined integrated absorption intensities and known ab sorption coefficients, we were able to determine the real concentration of impurities in the matrix etc. Because of the improved FTIR technic (high se nsitivity, resolution, accuracy) we studied in addition the overtone region of molecular excitations and investigated the kinetics of phase transition s; finally, we found spectroscopic evidence of impurity clusters and bands. Consequently, we are able to determine solubility limits of impurities in matrix (in our specific case this limit is about ppm).