The electronic structure of the GdF molecule was studied by means of four-component relativistic configuration interaction (CI) calculations [S. Yamamoto, H. Tatewaki, and T. Saue, J. Chem. Phys. 129, 244505 (2008)]. To analyze the electronic spectra more accurately, the CI wave function is decomposed according to the angular momentum (Ω(f)) generated from the (4f)(7) electrons. The weight of a specified Ω(f) is referred to as the "f-shell Omega component weight." This Ω(f) plays a crucial role in classifying the strong electronic transitions from the upper states (0.7 eV-3.0 eV) to the lower states (~0.55 eV). For these transitions, the upper and lower states have almost identical Ω(f) weights. This appears to be a necessary condition for a transition to be strong. The same condition is expected to hold for other lanthanide linear molecules. A point charge model is also studied, acting as a simplified model of GdF; it successfully reproduces the spectra of GdF, justifying studies based on ligand field theory.