Time-resolved Fourier transform infrared (FTIR) emission spectroscopy has been used to study the removal of methylene in its ground (CH2((X) over tilde B-3(1))) and first electronic excited state (CH2((a) over tilde (1)A(1))) in collisions with O-2. Both the singlet and triplet removal processes yield emission from vibrationally excited CO2 and H2CO, together with a weak component from CO. The production rate Of CO2 and H2CO was measured to be the same for the singlet and triplet processes and close to the rate of removal of (CH2)-C-3 by O-2, and the emission intensity was essentially unchanged by quenching the singlet to the triplet in collisions with Ar. We conclude that (CH2)-C-1 is quenched to (CH2)-C-3 in collisions with O-2 before reaction. (C) 2003 Elsevier Science B.V. All rights reserved.