The very weak absorption spectra of O-18(3) and O-16(3) have been recorded between 7700 and 7920 cm(-1) by high sensitivity cavity ring down spectroscopy (alpha min similar to 10 10 cm(-1)). The upper limit of the investigated region is only 6% below the dissociation energy. The spectrum consists in the superposition of very weak vibrational bands and unexpected broad absorption features which dominate in the case of the O-18(3) isotopologue. From recordings at temperatures ranging from 294 to 354 K, the broad features were identified as due to the (3)A(2)(0 0 0)-X(1)A(1)(1 1 0) hot band. The rovibronic levels of the (3)A(2)(0 0 0) state are predissociated and the widths of the corresponding lines range from 0.02 to at least 0.5 cm(-1). (C) 2011 Elsevier B. V. All rights reserved.