State-specific mobility of excited cadmium and calcium ions in a discharge plasma measured by a tunable diode laser.

Abstract

The state-specific drift velocity of Ca[sup +] ions in the 3 [sup 2]D[sub 3/2] metastable state and of Cd[sup +] in the 6 [sup 2][ital P][sub 3/2] highly excited state in a helium glow-discharge plasma have been precisely measured by using a tunable single-mode diode laser and the state-specific mobility of excited ions has been discussed. The results show that the mobility of Ca[sup +] ions in the metastable state is determined by momentum-loss collisions and is almost identical with the value for Ca[sup +] in the ground state. In the experiment with a thin cylindrical tube, the apparent value of the mobility is dependent on the diffusion in the radial direction. On the other hand, the apparent mobility of Cd[sup +] ions in the 6 [sup 2][ital P][sub 3/2] state is much smaller than the calculated result for Cd[sup +] in the ground state, but the value increases significantly with Cd vapor density. This is explained by the fact that Cd[sup +] ions in the 6 [sup 2][ital P][sub 3/2] highly excited state decay quickly by the radiative process and the apparent mobility of the Cd[sup +] ions in this state in the plasma is dependent not only onmore » the radiative lifetime but also on the excitation mechanisms for the state.« less