The decomposition of the spectrum presented on Figure provides additional insight. The spectrum shows that peaks B and C are almost purely of the 2 A 1 electronic and a 1 vibrational character. Starting from peak D, the contributions from two states are of equal magnitude. It is also clear that the following peaks are mixtures of many vibronic peaks. At the energy of about 2,000 cm -1 above the origin the density of vibronic peaks increases significantly.