Spectroscopic results, from an extensive study of rotationally resolved infrared-ultraviolet double resonance (IRUVDR) effects in the molecules D2CO and HDCO, are reported. The experiments involve rovibrational pumping (in the ν4 or ν6 bands of D2CO and the ν5 or ν6 bands of HDCO) and rovibronic probing of the A1A2 ← X1A1 electronic system (in the 40 1 or 60 1 bands of D2CO and the 50 1 or 60 1 bands of HDCO) with visible-fluorescence detection, using sequential pulsed excitation by CO2 and dye lasers. A remarkable result is the observation of IRUVDR rovibronic features in the very weak and heavily overlapped 60 1 band of D2CO, which has not previously been detected by conventional means. Further experiments which probe the 41 2 band of D2CO are interpreted in terms of single-photon rovibrational pumping in the (2ν4 - ν4) hot band, rather than two-photon pumping in the 2ν4 band. The results reported are obtained under effectively collision-free conditions, achieved by maintaining the product of pump-probe delay and sample pressure below ∼10 nsec Torr; collision-induced rotational and rovibrational relaxation is apparent when this product is increased. Other aspects of the IRUVDR technique which are considered include: the relation of IRUVDR results for D2CO and HDCO to coincidences between CO2-laser and molecular rovibrational frequencies, previously demonstrated by sub-millimeter optically pumped laser emission, infrared-radiofrequency double resonance, and Lambdip absorption studies; the role of saturation broadening in promoting multiple coincidences of molecular rovibrational transitions with a given CO2-laser line; relevance to mechanisms of infrared multiple-photon excitation of D2CO; inconsistencies between observed IRUVDR signal intensities and those anticipated from rovibronic transition probabilities.