| A new technique termed spatially resolved matrix isolation spectroscopy was invented. Three separate methods for obtaining uv/visible absorption data with a diode array rapid scan spectrometer (DARSS) were developed. A monochromatic detection source illuminates a lateral strip across a cryogenic matrix in the first method. By exploiting the rigidity of the matrix, the spatially resolved spectra can be parametrically labeled by another experimental variable, such as photolysis wavelength from dispersed radiation. The linear array of diodes records changes in the absorption spectrum of the matrix before and after photolysis. Alternatively, full uv/visible absorption spectra of individual regions of the matrix can be recorded when the DARSS/monochromator system is operated in a scanning mode. The absolute thickness of a matrix can be measured by these individual channel or diode spectra, allowing determination of the concentration of absorbing species in the matrix. The third method of DARSS operation is a rapid multiplexing mode in which the visible spectrum of a spatially uniform sample can be recorded in (LESSTHEQ)1 s, a speed which is important for photochemically active samples.;The feasibility of high spectral and spatial infrared detection using Fourier transform interferometric spectrometry was demonstrated with OCS/Ar matrices ((upsilon)(,1) band at 2049.6 cm('-1)).;From spatially resolved spectra of the Cr(CO)(,6) photosystem in argon matrices, three visible absorption bands of the photochemical products have been assigned: 569 nm - Cr(CO)(,5); 515 and 415 nm - Cr(CO)(,4). Gaussian functions fitted to the DARSS spectra allowed the half widths of the bands and the extent of overlap to be estimated. Under the given photolysis conditions, typical full widths at half maxima were 182, 139 and 37 nm respectively. Both Cr(CO)(,5) and Cr(CO)(,4) were primary photolysis products at 313 nm uv irradiation. It was determined that a photolysis energy of 91 kcal/mol is thus sufficient to break two Cr-CO bonds and produce electronically excited Cr(CO)(,5) and Cr(CO)(,4) fragments. Unfiltered uv photolysis with a Hg arc source produces the same species, but Cr(CO)(,5) also undergoes secondary decomposition to produce more Cr(CO)(,4). The recombination of Cr(CO)(,4) and Cr(CO)(,5) with ejected CO fragments was observed at visible photolysis wavelengths. |
