The isotope effect on the quenching of the cadmium triplet state by methanol

The isotope effect on the Cd-photosensitized emission of methanol has been investigated using CH3OH, CH3OD, CD3OH, and CD3OD. The relative quenching efficiencies for the 326.1 nm resonance line were 1 : 0.3 : 0.9 : 0.3 in the order of CH3OH, CH3OD, CD3OH, and CD3OD. The emission intensities from the intermediate complex between an excited cadmium and methanol were also measured. The band-shape was not affected by the substitution of D atoms. The intensity ratio was 1 : 3.1 : 1.1 : 3.1 in the order of CH3OH, CH3OD, CD3OH, and CD3OD, when the incomplete quenching was corrected. These results were explained by the following quenching processes: Cd* + CH3OH → Cd...H...OCH3 and/or Cd...CH3OH where Cd* represents Cd(3P1) and/or Cd(3P0). The D/H kinetic isotope effect on the former process was estimated to be 0.3. (auth.)