Optical absoiption

In other PANl systems protonated with HBF [266], HCl [261,278] and H2SO4 [303], temperature-independent susceptibility is observed. In PANI-CSA the electrical conductivity tr behaves as a metal, that is, a oc /T, above 200 K [304] and in PANl-HCI the microscopic conductivity obtained from the spin dynamics showed the semiconductor-to-metal transition around 150K [305,306]. Furthermore, the metallic optical absoiption was found in PANI-HBF, [280]. Then the temperature-independent susceptibility could be assigned to the Pauli susceptibility in these systems. 

The last example is the configuration, of which Mn, used in many luminescent materials, is a well-known representative. The Tanabe-Sugano diagram is given in Fig. 2.10. In octahedral coordination the ground level is A. All optical absoiption transitions are parity and spin forbidden. In fact the Mn ion is practically colorless. 

Figure i. Optical absoiption spectnim of thin film (0.7S/t) of MAI (17 %) polymer before and after exposure to intense short wavdength ultraviolet light, possible photochemical reaction mechanism, and observed refiracdve index changes in the film. 

FIGURE 52 Plot of the optical absoiption coefficient (a) as a function of photon energy ( ) for three samples (a H, top a-C H, middle and a-Sic H, bottom) along with the theoretical curves [134]. 

Fig. 2 Optical absoiption spectra of a solution of PcZn in N.N-Dimethylacetamide...

Figure 4-5. lNDO/SCl-calculalcd transition energies of the lowest two optical transitions of a cofacial dimer formed by two slilhcnc molecules as a function of interchain distance. The horizontal line refers to the transition energy of the isolated molecule. Note that the upper value reported at 3.S A corresponds to the transition to the fifth excited stale, which provides the lowest intense absoiption feature. 

Optical-Emission Spectrometer. Similar to flame photometer (atomic-absoiption photometer) except that an electric spark rather than a flame is used to vaporize (atomize) unknown samples. 

Figure 6. An optical set-up for the study of monolayers in a reflection-absoiption mode.

Electrothermal atomizers, which first appeared on the market in about 1970, generally provide enhanced sensitivity because the entire sample is atomized in a short period and the average residence time of the atoms in the optical path is a second ormore. Also, samples are introduced into a confined-volume furnace, which means that they are not diluted nearly as much as they would be in a plasma or flame. Electrothermal atomizers are used for atomic absoiption and atomic fluorescence measurements but have not been applied generally to emission work. They are, however, used to vaporize samples in inductively coupled plasma emission spectroscopy. 

Figure 5 shows the SFG vibrational spectra of carbon monoxide obtained at 10 -700 Torr of CO and at 295 K. When the clean Pt(lll) surface was exposed to 10 L (1 L=10 Torr sec) of CO in UHV, two peaks at 1845 cm and 2095 cm were observed which are characteristic of CO adsorbed at bridge and atop sites. LEED revealed that a c(4 X 2) structure was formed in which an equal number of carbon monoxide molecules occupied atop and bridge sites [15]. Such results are in agreement with previous HREELS [16] and reflection-absoiption infrared spectroscopy (RAIRS) [17] studies. ITie much higher relative intensity of atop bonded CO to bridge bonded CO in the SFG spectra is due to the specific selection rule for the SFG process [18]. As mentioned earlier, SFG is a second order, nonlinear optical technique and requires the vibrational mode under investigation to be both IR and Raman active, so that the SFG intensity includes contributions from the Raman polarizability as well as the IR selection mle for the normal mode. 

The LOAS instrument consists of the following main units A tunable laser, a sample cell with an acoustic transducer (sometimes called a spec-trophone or SP), an amplifier, and a recording system. The acoustic response of the medium can be stimulated by amplitude or frequency modulation of the laser light or by Stark or Zeeman modulation of the absoiption line of the analyte. Both pulsed and cw lasers with mechanical or electro-optical amplitude modulation are often employed in LOAS analytical applications. 

A molecule that undergoes a reversible photoinduced change between two states with different optical properties such as color or absoiption spectrum is considered to be photochromic. The chromogenic effect, photochromism, can be illustrated by the photochemical transformation of molecule A to B upon absorption of light ... 

Heras, A., Colina, A., Lopez-Palacios, J. et al. 2009. Flexible optically transparent single-waUed carbon nanotube electrodes for U V-vis absoiption spectroelectrochemistry. Electrochem. Commun. 11 442-445. 

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