High-energy excited state emission

In some cases a nucleus may exist for some time in one or more excited states and it is differentiated on this basis. Such nuclei that necessarily have the same atomic number and mass number are called isomers. "Co and Co are isomers the " Co nuclide exists in a high energy (excited) state and decays spontaneously by emission of a y-ray with a half-life of 10.5 min to the lowest aiergy, ground state, designated by Co. 

The 3 Pi/2, 3 P2/2 excited states involved in the sodium D lines are the lowest energy excited states of the atom. Consequently, in a discharge in the vapour at a pressure that is sufficiently high for collisional deactivation of excited states to occur readily, a majority of atoms find themselves in these states before emission of radiation has taken place. Therefore... 

Emission spectra of radical cations are obtained by vacuum UV ionization and subsequent laser excitation in noble-gas matrices (see below), or by electron-impact ionization of a beam of neutral parent molecules at energies above the first ionic excited state. After internal conversion to the first excited state, emission may compete more or less successfully with radiationless deactivation. If the experiment is carried out on a supersonic molecular beam one obtains highly resolved emission spectra which, in the case of small molecules, may contain sufficient information to allow a determination of the molecular structure. 

The high-energy excitation, hw, > h(o2 + hS20, is also due to the vibronic components at 390 and 1400 cm- . If we privilege the vibronic relaxation by fission and the creation of one vibration hQ0, then the relaxation of the incident photon h(ot leads to a state about 100 cm-1 above the observed emission. The excitation spectrum due to the vibronic component at 1400 cm-1 (see Fig. 3.18) shows that the relaxation by creation of other vibrations contributes also, since no threshold structure is observed around the value hco2 + 1400 cm-1. This conclusion is also consistent with the vibronic analysis of the bulk (Section II.B.3). 

Stilbene and Related compounds. The influence of sol-gel transformations on the emission spectra of cis and trans-stilbene has been assessed. The results of INDO/S calculations on stilbene has estimated the influence of the excited states involved in isomerization. The photostability of solutions of trans-stilbene to high-energy excitation with a XeCl laser has been studied. Geometric isomerization of both cis- and trans-stilbene is the result of irradiation of the compounds in NaY zeolites. A photostationary state composed of 65% cis and 35% trans is... 

The luminescence spectra of the above complexes demonstrate substantial Stokes shifts with respect to their excitation maxima. Again, this can be attributed to a highly distorted excited state structure with increased metal metal bonding interactions via population of a bonding orbital. The absorption and emission energies of (18) are significantly red-shifted compared to those of (17b). This size dependence is related to the quantum confinement effects observed in larger nanoclusters and colloids. This topic will be described further in Sections 1.2.1.2. and 1.2.6.3. 

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