Laser-ablated zirconium and hafnium atoms were reacted with CO molecules during condensation in excess neon. The Zr(CO)(x) and Hf(CO)(x) (x = 1-4) carbonyls formed during sample deposition or on annealing. Ultraviolet photolysis produced the OZrCCO and OHfCCO molecules by photochemical rearrangement of the Zr(CO)(2) and Hf(CO)(2) dicarbonyls where CO is activated in the metal complex. Evidence is also presented for the Zr(CO)(2)(-) and Hf(CO)(2)(-) anions. The product absorptions are identified by isotopic substitutions, electron trapping with added CCl4, and density functional theory calculations of isotopic frequencies. In contrast to the late transition metal carbonyl families, the carbonyl frequencies for TiCO, ZrCO, and HfCO decrease from 1920 to 1900 to 1869 cm(-1) in solid neon showing an increase in d-pi* back-bonding.