Radiative Lifetime of I2 Fluorescence, B 3II0+u→X 1Σ0+g

The radiative lifetime of the fluorescence of molecular iodine vapor, ${\mathrm{B\hspace{0.5em}}}^3{\mathrm{II}}_{0^{+}u}{\text{(v′=26)→X\hspace{0.5em}}}^1{\Sigma }_{0^{+}g}$ , has been determined to be (7.2±1.0)×10^—7 sec by using a phase fluorometer. Measurements on equilibrium vapor have been carried out over the pressure range 10^—4 to 5 mm Hg. Results at the lowest pressures are considerably shorter than the true lifetime due to mixing of scattered, incident light with the fluorescence. This effect has been corrected for analytically. At higher pressures the measured lifetime is shortened by self‐quenching. A Stern—Volmer plot of the data yields a self‐quenching collision diameter for I₂ of 11.3 Å. Measurements have also been carried out with a molecular beam of iodine vapor.