Excited-State Spectroscopy

The term excited state spectroscopy can have two different meanings, both of which will be treated in this chapter (I) probing the different excited stales of a material, the pathways to reach them, and the properties of these states and (2) a significant population of one or more of the excited states and the subsequent probing of the contribution of these states to the material s properties. Before going into details, a selected set of principal experiments in the area of excited states spectroscopy will be outlined. In order to detect the excitation process within a bulk material one can use ... 

Glasbeek M (2001) Excited State Spectroscopy and Excited State Dynamics of Rh(III) and Pd(II) Chelates as Studied by Optically Detected Magnetic Resonance Techniques. 213 95-142 Glass RS (1999) Sulfur Radical Cations. 205 1-87 Gobbi L, see Diederich F (1999) 201 43-129... 

Liihrs DC, Viallon J, Fischer I (2001) Excited state spectroscopy and dynamics of isolated adenine and 9-methyladenine. Phys Chem Chem Phys 3 1827... 

Zimmerer, G. Excited State Spectroscopy of Solids Grassano, U., Terzi, N., Eds. North Holland Amsterdam, Netherlands, 1987. 

The theoretical problems associated with calculating nonlinear polarizabilities is closely linked to the field of charge transfer spectroscopy and reactivity as well as the field of multi-photon and excited state spectroscopy. It is likely that theoretical methods from these fields will contribute to a deeper understanding of nonlinear optical phenomena in organic, inorganic, and organometallic compounds. 

A special case in the uranyl spectroscopy is formed by Denning s extensive work on the UO + group in Cs2U02Cl4C ([65], and papers cited therein). Later this work was extended to two-photon spectroscopy, a powerful method for a complex with inversion symmetry [66]. Excited state spectroscopy followed soon after [67], The latter experiments show a progression in the excited-state absorption spectrum of the UO + complex in a frequency of 585 cm-1. This is the U-O stretching frequency in the second excited state. In the first excited state it is at 715 cm-1. In this way it is possible to determine that the U-O distance expands from 1.77 A in the ground state to 1.84 A in the first and 1.95 A in the second excited state. This work has been reviewed recently [68]. 

G. Zimmerer, in Excited-State Spectroscopy in Solids, eds. U.M. Grassano and N. Terzi, North-Holland, Amsterdam, 1987, p.37. 

In view of the fundamental nature of the system more extensive and more precise data would be highly desirable as a test for bound state QED calculations. With the exception of the 1S-2S energy difference measurement, which is limited in precision by the laser wavelength measurement, all present experiments suffer from low statistics due to the small number of Ps atoms. It seems therefore worthwile discussing recent advances of increased Ps production and in parti-cular methods to populate the metastable 2 Sj state, which could serve as a basis for excited state spectroscopy. While laser excitation of states above n=2 from the ground state requires wavelengths between 205 nm (Lg) and 182 nm (ionization limit), which are very difficult to obtain with sufficient power, the corresponding wave-... 

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