Wavelength effects

As shown in Equation (14.4), Kerr-effect-induced birefringence seems to increase linearly with wavelength. However, such a relationship is not explicit because the Kerr constant K is also wavelength-dependent. Jiao, et al. conducted a nice experiment and proved that Kerr constant actually decreases with wavelength as [40] 

In this equation, the saturation electric field governs the electric behavior of blue phase LC, while saturated induced birefringence determines the optical behavior and thus the wavelength dispersion of blue phase. It still follows the normal dispersion trend and agrees very well with the single-band model. 

---

Ratiometric luminescent probes make a smart use of the excitation wavelength effect on the emission intensity for extended optosensor performance. For example, the fluorescence from 8-hydroxy-l,3,5-pyrenetrisulfonate (HPTS) and other pH-sensitive dyes in water comes only from its (photo)excited basic form, but the absorption spectra of HPTS and PTS (pAa 7.3) differ considerably (Figure 3). 

Consider continuous radiation with specific intensity I incident normally on a uniform slab with a source function 5 = Bv(Tex) unit volume per unit solid angle to the volume absorption coefficient Kp and is equal to the Planck function Bv of an excitation temperature Tcx obtained by force-fitting the ratio of upper to lower state atomic level populations to the Boltzmann formula, Eq. (3.4). For the interstellar medium at optical and UV wavelengths, effectively S = 0. 

Attention should be paid to possible problems in the measurement of fluorescence quantum yields (some of which are discussed Section 6.1.5) inner filter effects, possible wavelength effects on Op, refractive index corrections, polarization effects, temperature effects, impurity effects, photochemical instability and Raman scattering. 

As a final example we would like to note the reactions of quinone methide 27, which remains unchanged upon irradiation in methanol solution through a Pyrex or Vycor filter.128 Reduction is observed when 27 is irradiated in isopropyl alcohol with benzophenone or acetophenone,129 in methanol with acetophenone, or in methanol with no sensitizer through quartz.128 While the effect of ketone sensitizers is due to chemical sensitization,129 the wavelength effect is much more surprising. Further investigation showed that irradiation of methanol alone in a quartz vessel yielded ethylene glycol. The 185 nm line of the mercury arc, which is absorbed by Vycor and Pyrex, decomposes... 

Wavelength effects on the excess energy of the initially formed... 

Actually, type I cleavage occurs from both singlet and triplet excited states, as evidenced by the incomplete quenching of the photolysis of acetone by high pressures of biacetyl308 or 2-butene.243 The extent to which dissociation can be quenched is subject to large temperature and wavelength effects and depends markedly on the stability... 

The Mechanisms of Photochemical Reactions Quenching, Sensitization and Wavelength Effects... 

Substituent group Effect on wavelength Effect on intensity... 

The paper is organized as follows Section 2.2 briefly reviews the effect of the laser parameters. Section 2.3 describes the experimental methods and setups used in our group. Section 2.4 outlines our results regarding isomer ionization, wavelength effects, resonance mechanism, electron recollision, and excitation pulse width dependence. Section 2.5 describes FLMS including our recent application to dioxins and femtosecond time-of-flight (TOF) mass spectra are compared with those by electron impact excitation. Finally the contents of the paper are summarized in Sect. 2.6. 

A wavelength effect and a solvent effect have been reported in the photochemistry of 2,4-dichloroanisole380. Photolysis in cyclohexane and in methanol produces a mixture of 4-chloroanisole (A) and 2-chloroanisole (B). In cyclohexane A/B = 30-35 at 254 nm and 70-80 at 300 nm. In methanol the ratio changes from 2-3 at 254 nm to 55 at 300 nm. The authors speculate that direct S-T absorption at 300 nm might be responsible for the wavelength effect. 

Sattar, A., de Man, J.M., Alexander, J.C. 1977a. Wavelength effects on light-induced decomposition of vitamin A and (3-carotene in solutions and milk fat. Can. Inst. Food Sci. Technol. J. 10, 56—64. 

A disodium phenyl phosphate was also reported to photoeject electrons from the relaxed and unrelaxed St state. This may occur with different efficiencies, according to the pH, from the neutral, anionic or bis anionic species and a wavelength effect on the quantum yield was observed [82]. Hydrated electron has also been detected in the photolysis of ascorbic acid [83]. 

In contrast, previous studies with LP Hg lamps indicated that a very high UV fluence Hq of up to 8000 mJ cm is required to inactivate Cryptosporidium. This observation was initially assigned to the much lower irradiance E of LP Hg lamps compared with that of MP Hg lamps or to wavelength effects (Bukhari et al, 1999). LP Hg lamps can be treated as being almost monochromatic UV-C sources ( max= 253.7 nm) whereas MP Hg lamps emit polychromatic radiation in the germicidal range between 200 and 300 nm (cf Fig.s 4-5 and 4-6). 

---