INFRARED-SPECTROSCOPY AS AN INSITU PROBE OF MORPHOLOGY

Several factors contribute to the importance of infrared spectroscopy as an in situ probe for catalytic studies: these include its ease of application to a uniquely wide variety of substrates, its comparative insensitivity to gas-phase species, even at high pressure, and the availability of many model systems from spectroscopy in general and. more especially, from surface science and cluster chemistry. Additionally, it can be used not only to identify particular adsorbed species. but also to monitor catalyst morphology by the use of probe molecules such as CO, NO and N2. We show that in such structural studies attention must be paid to the role of intermolecular interactions, which can seriously distort the spectra. Under some conditions, profound changes in surface morphology may lead to no measurable alteration in the infrared spectrum, while. under other circumstances, variations of only a few percent in the occupancy of different adsorption sites may alter spectra quite massively. Sometimes, even the number of species present may be difficult to ascertain.