Electronic absorption spectroscopy oscillator strength

The excited states are of course studied directly through electronic absorption spectroscopy. The integrated intensity of an absorption band3), j (u)dv, relates theoretically to its oscillator strength (f). This, in turn, is proportional to the square of the electric dipole moment of a transition from the ground state (tpg) to the excited state (rpc) ... 

The cross section a is a fundamental property of the molecule and as such is related to the molecular wave functions for the two states between which a transition is induced. Hence it is desirable to separate the contributions to a that arise from purely kinematic quantities such as the impact energy of the electron beam from those that depend solely on the properties of the molecule. To this end, a dimensionless quantity, the oscillator strength, is introduced in optical absorption spectroscopy, defined by the relation22... 

Electron spectroscopy has become a useful tool for measuring optical oscillator strengths for absorption and ionization (fragment partial and... 

The electronic spectroscopy of trans-isomers of 3-(N-phenylamino)stilbene (mlc), 3-(N-methyl-N-phenylamino)stilbene (mid), 3-(N,N-diphenylamino)stilbene (mle), and 3-(N-(2,6-dimethylphenyl)amino)stilbene (mlf) and their double-bond constrained analogues, m2a-m2c and m2e, were studied [71]. When compared with trans-3-aminostilbene (mla), mlc-mle displayed a redshift of the So —> Si absorption and fluorescence spectra, lower oscillator strength and fluorescence rate constants, and more effldent Si —> Ti intersystem crossing. The N-Ph derivatives mlc-mle had lower fluorescence quantum yields and higher photoisomerization quantum yields. The role of Si —> Ti transition in the amino-substituted stilbenes as the predominant nonradiative decay pathway was discussed. The excited triplet (Ti) state formation of stilbene dendrimers (tetramethoxystilbene (generation G) GO, Gl,... 

One can use the PM technique with pulse excitations and study the time evolution of the spectra or the decay of the total oscillator strength of the bands. In this way one can obtain information about electronic relaxation processes. However, in this chapter we restrict ourselves to steady-state PM spectroscopy. We also note that instead of using illumination, the state occupation can be changed by changing the bias of a junction, as used in deep-level transient spectroscopy junction capacitance techniques. This method, dubbed charge-induced absorption, or CIA [44J, has already been used in conducting polymers and is discussed in another chapter of this book. 

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