The ionized gas in the Galactic Center Radio Arc

We present Infrared Space Observatory (ISO) observations of fine structure lines toward the Radio Arc region, close to Sgr A, in the Galactic center region (GCR). The ionization at large scale is dominated by the clusters of massive stars in this region: the Quintuplet and the Arches cluster. Any other possible mechanism as interaction with the magnetic fields revealed by the Non-Thermal Filaments (NTFs) must play a minor role. The radiation in this area is relatively hard ($T_\mathrm{eff}\sim 33-35$ kK) but diluted. It reaches large distances due to the inhomogeneity of the medium.