Electron-Impact Excitation out of the Metastable Levels of Krypton

We have measured the electron-impact excitation cross sections out of the two metastable levels of Kr into the ten levels of the $4p^{5}5p$ configuration. For a common $4p^{5}5p$ final level, the peak excitation cross sections out of the two individual $4p^{5}5s$ metastable levels are found to differ by 1 to 2 orders of magnitude. This is explained by the special features of the electronic structure of the two configurations involved. The peak cross sections are 10 to 1600 times larger than the corresponding peak cross sections out of the ground state.

Figure 1

Relevant energy levels of Kr labeled in both the Paschen and Racah notations. In Racah notation a level in the $4p^{5}nl$ configuration is denoted as $nl[K{]}_J$ where $K$ is the vector sum of $l$ and $J_c$, the total angular momentum of the $4p^5$ core. Levels with $J_c=1/2$ are denoted by a prime on the $nl$; levels with $J_c=3/2$ are left unprimed.

Figure 2

Collision region of the hollow cathode source of metastable Kr atoms.

Figure 3

Cross sections for excitation into the $2p_1$, $2p_3$, $2p_6$, and $2p_9$ levels from the $1s_3$ and $1s_5$ levels. Error bars are statistical only.

Figure 4

Cross section values for excitation into the $J=2$ $2p_2$ level. Note that the values for the $1s_5\to 2p_2$ cross section have been multiplied by ten.