| Popis: |
High-Rydberg atoms are produced by an electron beam passing through each of the rare gases at \ensuremath{\sim}${10}^{\ensuremath{-}6}$ Torr and are detected by electric field ionization after traveling 20.1 cm at thermal velocity. Their principal quantum number ($n$) distributions, time-of-flight distributions, absolute excitation cross sections ${\ensuremath{\sigma}}_{T}^{\mathrm{ex}}$, and excitation functions are measured. The atoms detected have $n$ ranging from 20-80 with the most probable $n$ varying with the gas from 28-46. From the measured ${\ensuremath{\sigma}}_{T}^{\mathrm{ex}}$ an apparatus-independent absolute cross section ${\ensuremath{\sigma}}^{\mathrm{ex}}(n,E) =\frac{{\ensuremath{\sigma}}^{\mathrm{ex}}(n=1,E)}{{n}^{3}}$, is determined. Values of ${\ensuremath{\sigma}}^{\mathrm{ex}}(n=1,E)$ range from 0.5-5 ${\mathrm{\AA{}}}^{2}$ at an incident electron energy $E=100$ eV. Ne and Ar measurements taken for different values of electron current and gas density demonstrate that low-angular-momentum ($l$) high-Rydberg atoms collide with electrons and/or ground-state atoms, causing higher-$l$ states to be populated. The $l$-changing cross section for collisions with electrons is estimated to be \ensuremath{\sim} ${10}^{6}$ ${\mathrm{\AA{}}}^{2}$ for Ne and Ar. |
