In the present study, a resolved optical-IR double resonance (OIRDR) spectrum was recorded for oxalylfluoride excited to the 4 31 3 21 , ð e A 1 A u Þ0 0 0 single rotational line. Assignment of discrete spectral lines and spectral simulations were done using the statistical model. It was found that in the presence of an IR field at an intermediate power level the decay of oxalylfluoride fluorescence is described by a biexponential function. This effect was explained taking into account the S-T, T-T and T-S dynamics. The observed phenomenon is a direct proof of the T-S transitions induced by internal S-T interactions. We found that NO affects the OIRDR spectrum, increasing the line widths. This effect was explained qualitatively by the VdW complex and cluster formation.