Experimental determination of parameters for molecular continuum radiation of rare-earth iodides

The molecular continuum radiation of high intensity discharges (HID) containing the rare-earth iodides TmI3, HoI3 and DyI3 in quartz burners have been investigated. For the case of TmI3 a more detailed analysis has been performed. Two main molecular emission contributions have been identified, being located in the arc core and in the mantle region. These molecular emissions turned out to deliver half of the total emission of this type of discharge. The mantle emission was identified as originating from the diatomic TmI. Two distinct upper energy levels at about 4 eV have been determined, being separated about 0.4 eV from each other. A pragmatic approach has been chosen to describe the spectral molecular emission coefficient as a sum of three Gaussian profiles. The proposed method allows one to take into consideration molecular emission for modelling of HID containing rare-earth iodides.