Explain why electronic spectra of metal complexes, peaks originated from electronic transition are broader
The main factors that cause broadening of the spectral line into an absorption band of a molecular solid are the distributions of vibrational and rotational energies of the molecules in the sample (and also those of their excited states).
The very broad absorption band is due to the excitation of the electron to various vibrationally excited states of the π* electronic state.
From spectral lines astronomers can determine not only the element, but the temperature and density of that element in the star. The spectral line also can tell us about any magnetic field of the star.