Photooxidation reactions of triphenylphosphine (Ph3P) monomers isolated in matrices of solid oxygen at 10 K were characterized by means of infrared spectroscopy. Upon UV (lambda > 280 nm) irradiation of O-2 matrices, ca. 90% of Ph3P was converted to triphenylphosphine oxide (Ph3P=O), with concomitant formation of ozone. In the competing photoreaction, ca. 10% of Ph3P was converted to diphenyl-phenyl-phosphinate, Ph-2(Ph-O-)P=O. The interpretation was assisted by theoretical [DFT(B3LYP)/6-31G(d,p)] calculations of vibrational spectra, as well as by comparison with the experimental vibrational data from separate experiments in which monomeric Ph3P and Ph3P=O were isolated in argon and oxygen matrices at 10 K. (C) 2008 Elsevier B.V. All rights reserved.