Wavelength of absorption maximum

In this project, we shall predict the wavelength of the absorption maxima of the same four polyenes using the calculated difference (in units of eV), between the LUMO and HOMO of these four molecules (Fig. 8-6). Bear in mind that this is not an ab initio calculation of wavelengths of maximum absorption, because empirically fitted parameters, Yio exist within the program or are... 

However, the direct determination of absorption at the wavelength of maximum absorption is more sensitive (or in the worst case at least as sensitive) as the indirect measurement of absorption by fluorescence or phosphorescence quenching. 

A solution of Fe(CN)e3- appears red. Using Figure 15.12, estimate the wavelength of maximum absorption. 

If we consider an absorption band showing a normal (Gaussian) distribution [Fig. 17.13(a)], we find [Figs. (b) and (d)] that the first- and third-derivative plots are disperse functions that are unlike the original curve, but they can be used to fix accurately the wavelength of maximum absorption, Amax (point M in the diagram). 

If the wavelength of maximum absorption of the analyte (Xmax) is known, it can be monitored and the detector may be considered to be selective for that analyte(s). Since UV absorptions are, however, generally broad, this form of detection is rarely sufficiently selective. If a diode-array instrument is available, more than one wavelength may be monitored and the ratio of absorbances measured. Agreement of the ratio measured from the unknown with that measured in a reference sample provides greater confidence that the analyte of interest is being measured, although it still does not provide absolute certainty. 

Most published data deals with model solutions to assess the major factors influencing betalain stability, among which pH and temperature are most frequently addressed. Until recently, total color loss was assessed by spectrophotometric monitoring of the decline at the wavelength of maximum absorption. To predict color fading over time, kinetic data were derived therefrom, most often obeying first-order decay principles. 

The wavelength of maximum absorption and the molar absorptivity are very dependent on pH, buffer, temperature, solvent, and the presence of other materials that may interact with anthocyanins. In addition, anthocyanin absorption follows a linear relationship with concentration only when present at low levels therefore considerable dilution is usually necessary. Absorbance normally should vary from 0.2 to 1.0 unit in order to obey Lambert-Beer s law. However, absorbance values as high as 1.5 to 2.0 absorbance units may be valid for sophisticated new instruments. 

Detection limits in the lOOfg range can be obtained with a tuneable UV laser working at a wavelength of maximum absorption for the compounds of interest. Continuous supersonic beams require high gas loads and combination with a pulsed ionisation technique (e.g. REMPI) is unfavourable in terms of sensitivity. Pulsed valves are a better approach for a GC-UV-MS interface [1021]. 

The quantum efficiency of fluorescence of a molecule is decided by the relative rates of fluorescence, internal conversion and intersystem crossing to the triplet state. Up to the present time it has proved impossible to predict these relative rates. Thus, whilst it is now possible to calculate theoretically the wavelengths of maximum absorption and of maximum fluorescence of an organic molecule, it remains impossible to predict which molecular structures will be strong fluorescers. Design of new FBAs still relies on semi-empirical knowledge plus the instinct of the research chemist. 

The spectral properties of these derivatives are similar to native rhodamine. The excitation maximum occurs at about 543 nm and its emission peak at 567nm, producing light in the orange-red region of the spectrum. The extinction coefficient of tetramethylrhodamine-5-(and-6)-iodoacetamide in methanol at its wavelength of maximum absorptivity, 542 nm, is 81,000M-1cm-1. 

For conjugated, non-aromatic substances, both the molar absorptivity and wavelength of maximum absorption increase. An example of this is the comparison of 1-hexene that absorbs at 177 nm with a molar absorptivity of 12,000 while 1,3,5-hexatriene absorbs at 268 nm and has a molar absorptivity of 42,500. 

The post-column ninhydrin reaction proceeds in a reaction coil at elevated temperatures (ca. I30-I35°C). Ninhydrin reacts with primary amino acids to give a chromophore with a wavelength of maximum absorption of 570nm. 

In order to plot the absorption spectrum of a compound or complex ion, we must be able to carefully control the wavelengths from the broad spectrum of wavelengths emitted by the source so that we can measure the absorbance at each wavelength. Additionally, in order to perform quantitative analysis by Beer s law, we need to be able to carefully select the wavelength of maximum absorption, also from this broad spectrum of wavelengths, in order to plot the proper absorbance at each concentration. These facts dictate that we must be able to filter out the unwanted wavelengths and allow only the wavelength of interest to pass. 

Figure 4 compares absorption spectra for membranes containing 10-and 30-nm-diameter Au nanowires. The wavelength of maximum absorption intensity for the membrane containing the 10-nm-diameter nano wires is blueshifted relative to that for the membrane containing the 30-nm-diameter nanowires. This blueshift for the smaller-diameter nanowires is... 

Two differential spectrophotometric methods were used by Chatterjee et al. for the simultaneous analysis of diloxanide furoate and metronidazole in pharmaceutical formulations [24]. The first method involved measurement of the absorbance of a methanolic solution of the two drugs at 259 and 311 nm. Since the absorbance of diloxanide furoate at 311 nm is zero, the concentration of metronidazole is directly measured, and a simple equation based on absorbance ratios is used to calculate the concentration of diloxanide furoate. The second method was a differential spectrophotometric determination based on pH-induced spectral changes, on changing from an acidic to an alkaline solution. A marked bathochromic shift was exhibited by metronidazole, while diloxanide furoate showed a slight hypsochromic shift. The wavelength of maximum absorption difference for diloxanide furoate was 267 nm, where metronidazole did not absorb. Similarly, diloxanide furoate did not interfere with metronidazole at when measured at 322 nm. 

The observed darkening of the indium slides results from a shift of the absorption peak because of the coating on the particles. Because of the cumbersomeness of the expressions for coated ellipsoids (Section 5.4) this shift can be understood most easily by appealing to (12.15), the condition for surface mode excitation in a coated sphere. For a small metallic sphere with dielectric function given by the Drude formula (9.26) and coated with a nonabsorbing material with dielectric function c2, the wavelength of maximum absorption is approximately... 

The wavelength of maximum absorption, and the corresponding e of a compound. Units are normally omitted from specifications of e. 

When the same reaction was carried out in the presence of L Ni2 +, the formation of Craq002+ in reaction 44 was followed by an absorbance increase at 360 nm, the wavelength of maximum absorption for L Ni i +. The rate of formation of L Ni i + and its yield exhibited little dependence on the initial concentration of L,Ni2 +. showing that the formation of oxidizing intermediates is rate determining. This observation places a limit on the rate constant for the scavenging reaction with UNi2-1- at > 108 M-1 s 1. 

Wavelength of maximum absorption (nm) Color absorbed Color observed... 

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