Excited Electronic transitions

While the T — 0 limit has been taken formally, it should be noted that the electronic fluctuation correlations at room temperature are essentially equivalent to those at T = 0 for normal, nondegenerate systems. (Thermal photons at room temperature are generally unable to excite electronic transitions )... 

Section I) and nuclear derivatives, which treat globally all the excited electronic transitions. In this subsection, we consider only Raman spectroscopy at low temperatures,47-79 as illustrated in Fig. 2.16. 

The energy of infrared radiation can excite vibrational and rotational transitions, but it is insufficient to excite electronic transitions. As shown in Figure 26-20, infrared spectra exhibit narrow, closely spaced absorption bands resulting from transitions among the various vibrational quantum levels. Variations in rotational levels may also give rise to a series of peaks for each vibrational state with liquid or solid samples, however, rotation is often hindered or prevented, and the effects of these small energy differences ai e not detected. Thus, a typical infrared spectrum for a liquid, such as that in Figure 26-20, consists of a series of vibrational bands. 

Another manifestation of the electrophilicity of bound NO + is given by photochemical activation, achieved by exciting electronic transitions that usually appear in the near UV-Vis region, finally leading to released NO.16 Equation 7.31 describes this process for SNP, which has been studied earlier.85... 

Many molecules absorb IR radiation, which corresponds to the vibrational and rotational transitions of the molecules. For this absorption to occur, there must be a change in polarity of the molecule. IR radiation is too low in energy to excite electronic transitions. There are a number of vibrations and rotations that the molecule can undergo (a few of these are shown in Figure 2.7) which all result in absorption of IR radiation. 

The vacuum u.-v. region begins at photon energies around 600 kJ mol (6 eV), sufficient to excite electronic transitions in all but the very simplest of molecules. The... 

Impinging monoenergetic electrons causing valence-electron excitations Electronic transitions... 

Visible and UV light sources, which excite electronic transitions, can be used also for PD spectroscopy. By scanning the frequencies of the radiation emitted from the UV/vis light source and measuring PD or electron photodetachment as a function of excitation wavelength, an electronic action spectrum can be constructed in the same way as a vibrational action spectrum is constructed using an IR source. 

With flame excitation, electronic transitions in alkali and alkaline earth metals, as listed in Table 1 are the most important. 

The interaction of radiation with matter can take many forms. The photoelectric effect, the Compton effect, and pair generation-armihilation are processes that occur at wavelengths shorter than those encountered in the infrared. Infrared photons can excite rotational and vibrational modes of molecules, but they are insufficiently energetic to excite electronic transitions in atoms, which occur mostly in the visible and ultraviolet. Therefore, a discussion of the interaction of infrared radiation with matter in the gaseous phase needs to consider only rotational and vibrational transitions, while in the solid phase lattice vibrations in crystals must be included. 

UV/visible spectroscopy involves absorption of electromagnetic radiation exciting electronic transitions between bonding (or nonbonding) and antibonding molecular orbitals. The most important transitions are n to % and % to i ... 

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