  The growing interest in atomic structures of moderately-stripped alkali-like
ions in diagnostic study and modeling of astrophysical and laboratory plasma
makes an accurate many-body study of atomic properties inevitable. This work
presents transition line parameters in the absence or presence of plasma
atmosphere for astrophysically important candidates, Ar$^{7+}$, Kr$^{7+}$,
Xe$^{7+}$, and Rn$^{7+}$. We employ relativistic coupled-cluster (RCC) theory,
a well-known correlation exhaustive method. In the case of a plasma
environment, we use Debye Model. Our calculations agree with experiments
available in the literature for ionization potentials, transition strengths of
allowed and forbidden selections, and lifetimes of several low-lying states.
The unit ratios of length and velocity forms of transition matrix elements are
the critical estimation of the accuracy of the transition data presented here,
especially for a few presented first time in the literature. We do compare our
findings with the available recent theoretical results. Our reported data can
be helpful to the astronomer in estimating the density of the plasma
environment around the astronomical objects or in the discovery of
observational spectra corrected by that environment. The present results should
be advantageous in the modeling and diagnostics laboratory plasma, whereas the
calculated ionisation potential depression parameters reveal important
characteristics of atomic structure.
