INFRARED-EMISSION SPECTROSCOPY WITH TRANSIENT COOLING

A new approach for collection of infrared spectral data from optically opaque materials is explored. This approach has previously been intro duced in the literature and is known as transient infrared transmissio n spectroscopy (TIRTS). The front surface of a hot sample is transient ly cooled with a jet of cold gas, and the ratio of the spectrum measur ed after cooling to that measured before cooling is shown to closely r esemble a transmission spectrum. This report provides for a more theor etical understanding of the experiments than provided by previous work ers, making use of unsteady-state heat flow calculations, harmonic osc illator modeling, and radiation transfer theory. Experimental data are collected from a solid polymer sample and two viscous liquid samples. The position of the spectral features for the emission measurements c orresponds with transmission measurements, with some saturation of the more intense spectral features noted. Faster scanning instrumentation , proper pulse scan synchronization, or rotation of solid samples, as demonstrated by previous workers, may resolve the saturation problem.