Study of S–T conversion induced by an external magnetic field in gaseous oxalylfluoride excited to the 00-level of the

The fluorescence intensity and decay of gaseous oxalylfluoride ((COF)2) excited to the 1Au(00) level by the Ã←X̃ transition were measured as a function of an external magnetic field. On excitation to this level, the dynamics in zero field may be described in the small-molecule limit, with the fluorescence exhibiting an almost exponential decay. However, at increasing field strength the initial fluorescence decay becomes faster, the decay profile becoming biexponential at higher fields. Thus, a magnetic field-induced change of dynamics occurs in the à 1Au state from that of a small molecule to that of the intermediate case. The fast-component decay rate constant Kf=(2.36±0.19)×107 s−1 is independent of the (COF)2 gas pressure and magnetic field strength, while the slow-component lifetime depends on both. We find that the magnetic field effect on the slow component grows at lower gas pressures. An increase of the integrated (COF)2 phosphorescence was observed at higher magnetic fields; consequently an external field accelerates singlet–triplet transitions in the excited (COF)2. Time-resolved measurements of the effect of a microwave field on the fluorescence demonstrated that the slow-component amplitude and lifetime are additionally reduced by an external microwave field, at νMW=9400 MHz, B=0.3295 T, and P=30 mTorr; and the fast-component amplitude increases at constant lifetime. We also find an additional phosphorescence intensity increase with subsequent saturation at higher microwave intensities. Experimental data are interpreted using the indirect mechanism theory in the low level density limit.