A competitive technique employing the SO2(3B1) photosensitized isomerization of cis‐C2F2H2to trans‐C2F2H2in the presence of various aromatics has been used at 3660Å and 22°C to determine the rate constants of the quenching reaction SO2(3B1) + Mk4?removal. Using PSO2= 25.1 Torr and Pcis‐C2F2H2= 0.230 Torr the results from Stern‐Volmer plots gave k4estimates (units oflmole‐1sec‐1× 1011) of 0.883 ± 0.085, 1.43 ± 0.13, 2.04 ± 0.19, 2.17 ± 0.26, 2.29 ± 0.20, and 2.15 ± 0.19 for M = benzene, toluene, ethyl benzene, o‐xylene, m‐xylene, and p‐xylene, respectively. These results indicate that increasing the e‐density in the aromatic nucleus due to e‐releasing alkyl substituents results in an increase in the magnitude of k4. However, the o, m, and p‐xylene results indicate that the value of k4is not sensitive to the position of the alkyl substituent on the aromatic ring.