Wavelength extension

If these materials are deposited as LB multilayers, polymerization can be induced either by thennal or optical means. This subject has been intensively studied [95, 96, 92, 98 and 99]- Since parameters such as m, subphase components, pH and polymerization before and after dipping, as well as temperature and wavelength employed for polymerization can be varied, the literature on diacetylenes is extensive and the reader is referred for example to the book of Tredgold [1001. 

Table 7.8 contains values of p,/p for the common target elements employed in X-ray work. A more extensive set of mass absorption coefficients for K, L, and M emission lines within the wavelength range from 0.7 to 12 A is contained in Heinrich s paper in T. D. McKinley, K. F. J. Heinrich, and D. B. Wittry (eds.). The Electron Microprobe, Wiley, New York, 1966, pp. 351-377. This article should be consulted to ascertain the probable accuracy of the values and for a compilation of coefficients and exponents employed in the computations. 

Many of the physical properties are not affected by the optical composition, with the important exception of the melting poiat of the crystalline acid, which is estimated to be 52.7—52.8°C for either optically pure isomer, whereas the reported melting poiat of the racemic mixture ranges from 17 to 33°C (6). The boiling poiat of anhydrous lactic acid has been reported by several authors it was primarily obtained duriag fractionation of lactic acid from its self-esterification product, the dimer lactoyUactic acid [26811-96-1]. The difference between the boiling poiats of racemic and optically active isomers of lactic acid is probably very small (6). The uv spectra of lactic acid and dilactide [95-96-5] which is the cycHc anhydride from two lactic acid molecules, as expected show no chromophores at wavelengths above 250 nm, and lactic acid and dilactide have extinction coefficients of 28 and 111 at 215 nm and 225 nm, respectively (9,10). The iafrared spectra of lactic acid and its derivatives have been extensively studied and a summary is available (6). 

Extensions in wavelength, into both the infrared and the ultraviolet ranges will continue, motivated by increasing interest in narrow band-gap semiconductors and wide band-gap materials. 

All infrared spectrophotometers are provided with chart recorders which will present the complete infrared spectrum on a single continuous sheet, usually with wavelength and wavenumber scales shown for the abscissa and with absorbance and percentage transmittance as the ordinates. More advanced instruments also possess visual display units on which the spectra can be displayed as they are recorded and on which they can be compared with earlier spectra previously obtained or with spectra drawn from an extensive library held in a computer memory. These modern developments have all led to quantitative infrared spectrophotometry being a much more viable and useful analytical procedure than it was just a few years ago. 

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