Although full rate and branching ratios require complicated multi-well calculations, some qualitative predictions can be made by simply considering the LZ formula, Eq. ( ). This expression indicates that the non-adiabatic (here, triplet-singlet) transitions are suppressed when the velocity of crossing is high. Since the MECPs heights in the ethylene-and propylene-derived diradicals are small, the ISC is likely to proceed as follows: oxygen attaches to one of the carbons, the intermediate collides with other molecules and loses ro-vibrational energy, low 4.4 • 10 3 a All-harmonic mode approximation was used for all the rates reported above. The total rate of ISC (shown in the same row as acetylene, propyne, etc) is a sum of the rates of from all intermediates.