Excited-State Intermolecular Interactions Involving Paramagnetic Molecules: Effect of Spin—Spin and Spin—Orbit Interactions on the Quenching of Triplets

The effects of spin‐spin interactions on the rate constants, k_q, for the quenching of excited triplet‐state molecules by molecular oxygen and NO have been examined. Depending upon the strength of the electrostatic interactions between the excited triplet‐state molecule and molecular oxygen, k_q may vary from k_d, the diffusion‐controlled value, down to $k_d\text{/9}$ . In agreement with experimental observations, oxygen is predicted to be a better triplet‐state quencher than is NO. The analysis also suggests that through application of sufficiently high magnetic fields, it should be possible to observe changes in the quenching constant and that this effect could be used to obtain information about the nature of the electrostatic interactions which are present in the collision complex between the excited triplet‐state molecule and paramagnetic quenchers.