Rydberg-to-$M$-shell x-ray emission of hollow ${\text{Xe}}^{q+} \left(q=27–30\right)$ atoms or ions above metallic surfaces

X rays originating from transitions from high Rydberg states to the $M$ shell (here called Rydberg-to-$M$-shell x rays) have been measured in the interaction of ${\text{Xe}}^{q+}\left(q=27–30\right)$ ions with aluminum, molybdenum, and beryllium surfaces in the energy range of 350–600 keV, by using a Si(Li) detector. The transition energy calculation by Cowan's program with relativistic correlation indicates that such x rays are mainly from the transition of the higher quantum states, with the principal quantum number from 6 up to 30, directly to $M$ shell of xenon. The yield of the x ray per vacancy in $M$ shell decreases slightly with increasing the projectile energies and is inversely proportional to the work functions of metallic surfaces used. However, it increases rapidly with the increase of the projectile charge states. All of these experimental facts combined with the transition rate calculations indicate that the measured Rydberg-to-$M$-shell x rays come from the “above the surface” hollow Xe atoms or ions deexcitation, when the inner shells such as $N$ and $O$ have not been filled.

Figure 1

X-ray spectra emitted in the interaction of 450 keV ${\text{Xe}}^{q+}\left(q=25–30\right)$ ions with Al surface. For initial charge state $q=25$ and 26 only lower-intensity backgrounds primarily from Si escape x rays are observed, and for $q=27$–30 higher-intensity Rydberg-to-$M$-shell x rays are observed as well as shifts in energies.

Figure 2

Xe Rydberg-to-$M$-shell x-ray yields following ${\text{Xe}}^{30+}$ ions impact on Al surfaces as a function projectile energies from 350 to 600 keV.

Figure 3

Xe Rydberg-to-$M$-shield x-ray yields divided by the initial number of $M$-shell vacancies as a function of projectile charge states for ${\text{Xe}}^{q+}\left(q=27–30\right)$ ions impact on Al surfaces with incident energies $\square$ 350, $◯$ 400, $△$ 450, $▽$ 500, $♦$ 550, and $⊲$ 600 keV, respectively. The B-spline line represents the arithmetic mean values over the yields induced by ions with different kinetic energies.

Figure 4

Averaged Xe Rydberg-to-$M$-shield x-ray yields per $M$-shell vacancy as a function of projectile charge states for ${\text{Xe}}^{q+}\left(q=27–30\right)$ ions impact on Al, Mo, and Be surfaces.