Phosphorescence quenching of biacetyl vapor by alcohols and iodides

The quenching of phosphorescence emission from biacetyl, excited at 404.7 nm, has been investigated in the gas phase for several alcohols and iodides. The data gave linear Stern—Volmer plots, from which quenching rate constants for collisions of 3 B u biacetyl were determined. The rate constant values in l/mol s were: methyl alcohol (7.6 × 10 5 ), ethyl alcohol (6.2 × 10 5 ), n-propyl alcohol (7.2 × 10 5 ), methyl iodide (1.0 × 10 6 ), ethyl iodide (1.1 × 10 6 ), n-propyl iodide (6.7 × 10 5 ), and methylene iodide (2.9 × 10 6 ). Using simple hard sphere collision theory, the collisional efficiencies of quenching, per gas kinetic collision, were all in the range 2 to 5 × 10 −6 , except for methylene iodide, which was 1.4 × 10 −5 . The quenching mechanism for the alcohols is most probably H-atom transfer from the alcohol to 3 B u biacetyl. For the iodides, the data cannot be used to distinguish unambiguously between an external heavy atom effect and chemical quenching.