Excitation energy excess

Figure 9. Effect of increasing the excess excitation energy on the LIE spectra of II in a supersonic jet expansion. TOP mass spectra (right) indicate that the emission spectra (left, bottom) correspond to the monomer. The numbers indicate the wavelengths of excitation (in nm).

In cyclotrons charged particles such as protons, deuterons, and a-particles bombard the target nuclei, and after emission of one or more particles to remove the excess excitation energy, a radioactive product nuclide may result. In the capture of positively charged particles and the subsequent emission of neutrons the product radionuclides are neutron deficient compared to the stable isotopes of the elemoit see Fig. 3.1 and 4.7. Another important point in cyclotron bombardments is that normally the product is not isotopic with the target. As a result, after chemical separations a product of high specific activity is obtained since it is not diluted by the target material. An example of an important cyclotron-produced radionuclide is Na (ti 2.6 y) formed by the reaction ... 

Taken together, 8-carotene displays three functions in LHC I. This carotenoid is associated with the long-wavelength chi forms (6) which act as an energy sink in LHC I upon closure of the reaction centres (7). Recently we have shown that at least some of the 8-carotene molecules in the isolated LHC I are involved in photoprotection (4). Consequently we conclude that these 8-carotene molecules shield the energy valve system of the native PS 1-200 complex from excessive excitation energy. 

A regulatory mechanism to dissipate excess of excitation energy during high light exposure has been proposed to partially protect leaves from photoinhibition of PS2 photochemistry <9, 10). This mechanism is the non-radiative energy dissipation of excess excitation energy where the xanthophylls cycle may play an Important role (11). 

Karpinski S, Reynolds H, Karpinska B, Wingsle G, Creissen G, and Mullineaux P. Systemic signaling and acclimation in response to excess excitation energy in Arabidopsis. Science 1999 284 654-657. 

Young, A.J., Phillip, D., Ruban, A.V., Horton, P., Frank, H.A. The xanthophyll cycle and carotenoid-mediated dissipation of excess excitation energy in photosynthesis. Pure Appl. Chem. 69, 2125-2130 (1997)... 

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