chlorineVII

Chlorine VII (Cl VII) is the seven-times ionized state of chlorine, corresponding to chlorine with a +6 charge (Cl6+). In spectroscopy and atomic physics, the roman numeral indicates the ionization stage; thus Cl I is neutral chlorine, Cl II is singly ionized, and Cl VII is six electrons removed. Cl VII is isoelectronic with sodium (11 electrons).

Formation and environment: Cl VII forms in high-temperature plasmas where a significant portion of chlorine has been stripped of electrons, typically at temperatures exceeding several hundred thousand kelvin. It is encountered in astrophysical environments such as stellar coronae, hot interstellar and intergalactic plasmas, planetary nebulae, and in laboratory fusion devices.

Spectral characteristics: As a Na-like ion, Cl VII has energy levels and transitions that produce lines primarily in the extreme ultraviolet and soft X-ray regions. The lines are used in plasma diagnostics to infer electron temperature and density and to determine chlorine abundances in hot plasmas when ionization balance models are available.

Measurement and theory: Analysis relies on collisional-radiative modeling and atomic data for Na-like ions, including energy levels, transition probabilities, and collision cross sections. Observational data are obtained with space-based UV/EUV and X-ray spectrometers and compared to models to estimate ionic fractions and element abundances.

See also: Chlorine, Ionized chlorine, Sodium-like isoelectronic sequence, Solar corona, Planetary nebula.