The excitation of the dissociated iodine atom to the state of $I(5^2 P_{\frac{1}{2}})$ is achieved by the short electric pulse discharge in the mixture of gaseous $CF_3I$ and the buffer gases Ar, $N_2$. The infrared radiation (1.315 μm) emitted by the transition of iodine atom from $5^2P_{\frac{1}{2}}$ to $5^2P_{\frac{3}{2}}$ state is detected by a Ge PIN photodiode with the infrared filter with narrow bandpass transmission at $\lambda$ = 1.3 μm.
The buffer gases Ar, $N_2$ are found to play an important role in formations of glow discharge and for the stabilization of the cavity in the discharge process. The measured value of the effective life time $\tau_{eff}$ of the excited iodine atom $I(S^2P_{\frac{1}{2}})$ is about 200 $\mu\sec$ at the pressure 0.5torr of $CF_3I$ and 40-100 torr of Ar, and 100-200 $\mu\sec$ at the pressure 0.5 torr of $CF_3I$ and 15-20 torr of $N_2$, which is far smaller than the life time, 0.13 $\sec$, of the spontaneous transition calculated by Gastang or Zuev. Over the pressure 0.5 torr of $CF_3I$, the cavity is very unstable and glow discharge is impossible. The quenching effect or the deactivation effect of $O_2$ and $I_2$ upon the iodine $5^2P_{\frac{1}{2}}$ state seems quite large, but the pressure of the buffer gases has the least effect on the life time of the excited iodine atom. So, the oxygen should be removed most in a vacuum system prior to the inlet of $CF_3I$ gas. Another important factor for glow discharge is electrode shape. The design of the discharge chamber and electrodes are changed several times for the uniform glow discharge and finally the Change's profile is adopted.
