Electronic absorption ladder

In Fig. 14, the UV spectra of the domino oxidation products are shown. As the number of oxatetrasilacyclopentane rings increases, the lowest energy absorption maximum shifts bathochromically, and the molecular extinction coefficient becomes far larger (10 270 nm (s 3200), 11 273 nm (s 7600), 12 292 nm (s 25000), 13 297 nm (s 51900). The intense absorption of the order 104 is remarkable because these molecules contain no obvious chromo-phores which should give such intense absorption. Since the intense absorption is not observed in the ladder polysilanes, it is apparently due to the electronic effect of the oxygen atoms on the Si-Si a conjugation systems. 

Instead of the ladder C model, the ladder H model, where the electrons of the bonds to substituents in addition to those in the backbone are considered, is suggested to be essential for drawing even the simplest picture of a conjugation35. The A states are also of a aa and a an type, and are calculated to undergo a similar avoided crossing. In view of their very low calculated absorption cross sections, they could be detected only by two-photon absorption spectroscopy. 

The wavefunctions for three-dimensional confinement have three quantum numbers (n, I, m) plus spin. The selection rules for dipole-allowed absorption and emission were given above for interband transitions. For intraband transitions between the ladder of electron or hole states, the selection rules for the simplest case of non-interacting electrons and holes are An 0 AL = 0, + 1 Am = 0, + 1. 

There are excellent coincidences between vibration rotation transitions of the NO fundamental in the X n and some strong CO-laser lines near 5.2 jim. If we shine a few watts of this co-laser light into an absorption cell containing NO and Ar, those y- and p-bands occur at IR-laser power densities of less than 1 kW/cm. This means that there must be a way for the energy that is put into the fundamental vibration of the diatomic molecule to get up the ladder of vibrational states to the level of electronic excitation or to the dissociation limit [3,2/3,3]. For a diatomic molecule, particularly at these low power densities, multiphoton excitation is not possible. 

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