Combination transitions

In addition to bands in the infrared and Raman spectra due to Au = 1 transitions, combination and overtone bands may occur with appreciable intensity, particularly in the infrared. Care must be taken not to confuse such bands with weakly active fundamentals. Occasionally combinations and, more often, overtones may be used to aid identification of group vibrations. 

The miscibilities of the components in polymer blends is often ascertained by the measurement of the material s glass transition temperature (Tg). The mixing of two polymers with no mutual interactions usually results in the mixture having two separate phases each with their own distinct glass transition temperature. However, when the two components do interact to form a single phase mixture, their glass transitions combine and there will be the emergence of only one transition temperature that is linearly dependent on composition [118]. 

Note that the equilibrium difference across the DQ transition (Paa - Ppp) is 45 because the energy separation is twice that of an SQ transition. Combining all three terms,... 

Carrier and exciton dynamics in InGaN/GaN MQWs have also been studied at a high optical pumping power [34], At 7 K, a radiative decay lifetime of 250 ps was observed for the dominant transition at a generated carrier density of 1012/cm2. The time-resolved measurement showed that the decay of PL has a bimolecular recombination characteristic. At room temperature, the carrier recombination was found to be dominated by non-radiative processes with a measured lifetime of 130 ps. Well width dependence of carrier and exciton dynamics in InGaN/GaN MQWs has also been measured [35]. The dominant radiative recombination at room temperature was attributed to the band-to-band transition. Combined with an absolute internal quantum efficiency measurement, a lower limit of 4 x 10 9 cm3/s on the bimolecular radiative recombination coefficient B was obtained. At low temperatures, the carrier... 

We are now in a position to understand the remarkable simplicity of the hne spectra of hydrogen, first discovered by Balmer. We recognize that the line spectra are the result of emission, so fiphoton = hv = hc/X = —AE for these transitions. Combining Equations 6.5 and 6.6 we see that... 

We also failed to detect by LIF any electronically excited A10(A Ili) product, by excitation on B-A transitions in the fundamental range of rhodamine dyes, and collecting the fluorescence of B-X transitions. Combined factors are certainly responsible for the low LIF signals the spread of the products on the large manifold of accessible rovibrational states, the high recoil velocities which lower the densities, and perhaps a lower reactive cross-section than for the other reactions. 

Both the vibrational and the rotational energy transitions that occur in the fundamental transitions combine to make up the fundamental absorption band. When the vibrational quantum number change is... 

Figure 2.8 Contributions of the different electronic transitions to the excited state character for each of the studied systems. Red gives the contributions of intra-band (IB) transitions, green depicts single exciton (SE) transitions, blue corresponds to IB transitions combined with exciton transitions (IB-I-SE) and black shows ME transitions. The data points are the squares of the SAC-CI expansion coefficients for the corresponding transition types. Only every fifth data point is plotted for clarity. The lines give the average behavior of the respective transition type.

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