P-branch emission spectra of the A¹\Pi–X¹Σ⁺ system of IrN

The P-branch emission spectra of (4,1) and (3,1) bands of the A¹\Pi-X¹Σ⁺ system of IrN molecule are studied using an analytical formula which is derived from elementary expression of molecular total energy by taking multiple spectral differences. It not only reproduces the known experimental transition lines, but also predicts the unknown spectral lines up to J= 80 for each band by using a group of fifteen known experimental transition lines.