The MO(CO)(5)(+)(M = Sc, Y, La and Ce) complexes are generated and analyzed using an infrared photodissociation spectrometer. Their C-O stretching frequencies are determined to be 2210 cm(-1), 2206 cm(-1), 2198 cm(-1) and 2196 cm(-1) for M = Sc, Y, La and Ce, respectively. The simulated spectra from DFT calculations are compared with the experimental results, indicating MO(CO)(5)(+) (M = Sc, Y, La and Ce) are or very close to pentagonal pyramidal structures with C-5V symmetry. The comparisons of these complexes with other metal carbonyls help to elucidate the characteristics of CO coordination in various metal species. (C) 2015 Elsevier B.V. All rights reserved.