Simulation of the A–X and B–X transition emission spectra of the InCl molecule in low pressure plasmas

Low pressure plasmas containing indium halides as radiators are discussed for lighting applications as an efficient alternative to mercury-containing fluorescent lamps. To gain insight into plasma parameters like the vibrational and rotational temperature of the molecule, the near UV emission spectra of the indium halides arising from the AΠ0+3→XΣ+1 and the BΠ13→XΣ+1 transitions are simulated. Such a simulation requires Franck–Condon factors and vibrationally resolved transition probabilities which are not available in the literature for InCl. Therefore, they have been calculated by solving the Schrödinger equation using the Born–Oppenheimer approximation. The values of the Franck–Condon factors and the transition probabilities are presented. For the A–X transition a good match of the simulated and measured spectra could be achieved but for the B–X transition neither the relative intensity nor the wavelength could be reproduced. This indicates that for the B state the values of the molecular constants, the potential curve and/or the electronic dipole transition moment of the B–X transition are inaccurate. Despite this mismatch the rotational and vibrational temperatures of the molecule can still be determined using the A–X transition.