The (1 0(0) 5)1,2 --> (1 0(0) 4)1,2 and (1 0(0) 6)1,2 --> (1 0(0) 5)1,2 emission bands of 12C16O2 have been recorded near 4.5 µm by Fourier transform spectroscopy of a CO2 + N2 mixture excited by dc discharge. The spectroscopic parameters of the (1 0(0) v3)1,2 vibrational states with v3 = 0-6 have been obtained from a global rotational analysis of the six (1 0(0) v3)1,2 --> (1 0(0) (v3-1))1,2 emission bands (v3 = 1-6). The (1 0(0) 5)1,2 vibrational states of both 12C16O2 and 13C16O2 have been observed by direct absorption from the vibrational ground state by Intracavity Laser Absorption Spectroscopy near 12 700 and 12 400 cm-1, respectively. The rovibrational energy levels obtained by the two experimental techniques are discussed and compared with those calculated in the framework of the effective operator approach. Copyright 1999 Academic Press.