Collisional-Rate Coefficients for Sodiumlike Ar viii Ions

Collisional-excitation-rate coefficients for sodiumlike Ar viii ions have been obtained theoretically using the Coulomb-Born approximation as well as experimentally from the absolute intensities of lines emitted by these ions in well-diagnosed plasmas whose parameters were obtained from the analysis of scattered laser light. These plasmas were produced in a $\theta$-pinch device. The agreement between theory and experiment is within the estimated accuracy of ±50% for excitation from the ground state to the $n=3\mathrm{}$ and $n=4\mathrm{}$ levels, whereas some deviations are observed for two transitions to the $n=5\mathrm{}$ levels at lower temperatures. A rate coefficient for ionization was obtained from the time dependence of the ionization.