Infrared matrix isolation spectroscopy has been employed to characterize monomeric silicon difluoride. Warm-up experiments show the development of several sets of new bands which indicate that this molecule polymerizes through a reactive dimeric intermediate. Other reactive molecules were mixed with the matrix gas and deposited with silicon difluoride on the cold window. When these heterogeneous matrices were allowed to warm up, new bands characteristic of the reaction products of silicon difluoride with the secondary species were observed to appear. In this manner the reactions of silicon difluoride with boron trifluoride, carbon monoxide, nitric oxide, oxygen and perfluorobenzene were observed and the reaction products spectroscopically identified.