Water vapor absorption spectrum

The fundamental V3, which is an A band, appears at 1500.6 cm" Water vapor absorption makes it difficult to examine the fine-line structure of this fundamental. The spectrum shown in Figure 4-37 has been measured in a vacuum spectrophotometer, so that the absorption from water appears only at the extreme edge of the R-branch of the formaldehyde band. 

The ultraviolet absorption spectrum of thiazole was first determined in 1955 in ethanolic solution by Leandri et al. (172), then in 1957 by Sheinker et al. (173), and in 1967 by Coltbourne et al. (174). Albert in 1957 gave the spectrum in aqueous solution at pH 5 and in acidic solution (NHCl) (175). Nonhydroxylic solvents were employed (176, 177), and the vapor-phase spectrum was also determined (123). The results summarized in Table 1-15 are homogeneous except for the first data of Leandri (172). Both bands A and B have a red shift of about 3 nm when thiazole is dissolved in hydrocarbon solvents. This red shift of band A increases when the solvent is hydroxylic and, in the case of water, especially when the solution becomes acidic and the extinction coefficient increases simultaneously. 

The following physico-chemical properties of the analyte(s) are important in method development considerations vapor pressure, ultraviolet (UV) absorption spectrum, solubility in water and in solvents, dissociation constant(s), n-octanol/water partition coefficient, stability vs hydrolysis and possible thermal, photo- or chemical degradation. These valuable data enable the analytical chemist to develop the most promising analytical approach, drawing from the literature and from his or her experience with related analytical problems, as exemplified below. Gas chromatography (GC) methods, for example, require a measurable vapor pressure and a certain thermal stability as the analytes move as vaporized molecules within the mobile phase. On the other hand, compounds that have a high vapor pressure will require careful extract concentration by evaporation of volatile solvents. 

Fig. 1.6 Absorption spectrum for water (gaseous, solution, and liquid). Above the vapor band is Mecke s rotational analysis [11,12].

Basila (365) studied the izifrared spectrum of silica-alumina dehydrated at 500°. The technique developed by Peri and Hannan (333) was used. Only one OH stretching frequency at 3745 cm- was observed. This coincides with the absorption of isolated hydroxyl groups on pure silica. The absorption peak is not influenced by the chemisorption of water vapor at 150°. The chemisorbed water retains its molecularity, does not form hydrogen bonds with the isolated silanol groups, and is adsorbed on sites which can be poisoned by treatment with potassium acetate. 

Figure 6 illustrates another highly developed application of our FTIR facility. Trace (A) shows the complete absorbance spectrum, 600-3600 cm-1, of a CVS bag sample of a typical auto exhaust. While dominated by water vapor and CO2 absorption, several interesting features are visible. For instance, the carbon monoxide band is readily apparent, as is absorption due to heavy hydrocarbon (indicated by the broad unresolved C-H stretch band). In Trace (B) absorption due to CH4, NO2, formaldehyde and as well, water and heavy hydrocarbon can clearly be seen. In Trace (C),... 

It was known long ago that a discharge in water vapor splits water into OH and H. The properties of OH in the zone of electric discharge have been discussed i n a great number of papers. The first works in which hydroxyl was detected in the zone of discharge in water vapor by means of its absorption spectrum were those of Oldenberg23 and by Kondratiev and Ziskin.17... 

A sharp decrease in the hydroxyl concentration was observed when small amounts of CO or of hydrocarbon penetrated into the discharge tube. It might be such as to prevent detection of hydroxyl by its absorption spectrum. In order to restore the hydroxyl concentration it was necessary to clean the discharge tube and the reaction vessel by means of a discharge with water vapor lasting for several hours. For instance, after having worked with benzene without controlling the presence of hydroxyl, the latter was not detected in the reaction vessel. 

The photolysis of water vapor has been studied in the region from 1295 to 1650 A. The results of a recent and reliable study by Watanabe and Zelikoff (102) of the absorption coefficients in this region are shown in Figure 6. They have also obtained the spectrum at shorter wave-... 

Fig. 6. Absorption spectrum of water vapor. This figure is taken from ref. (102) with the permission of the Journal of the Optical Society of America.

Since PM-IRRAS is insensitive to the strong IR absorption of water vapor, it has proved to be an efficient way to study the conformation and orientation of protein molecules because only important bands arising from the monolayer are observed [72,97-103], The first in situ study of the protein conformation by PM-IRRAS technique was reported by Dziri et al. [97]. The vibrational spectrum of acetylcholinesterase (AChE) at the air-water interface in its free form and bound to either its substrate or organophosphorus (OP) inhibitor was measured. PM-IRRAS spectra collected during compression of the AChE... 

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