Absorption spectrum absorbance

A covalent Unkage between two bacteriochlorophyll a molecules results in a species which in the presence of the proper bifunctional ligand (e.g., ethanol) undergoes folding like the chlorophyll a dimer. It does not reproduce the in vivo absorption spectrum, absorbing at 803 nm instead of 870 nm. Yet, it does have a delocalized cation and a delocalized triplet state. 

Since the absorption spectrum is a ratio it is amenable to other interpretations. One such interpretation is that the absorption spectrum is the ratio of energy absorbed to energy incident. From this perspective, the quantity /)co(d/d0< li 0l f 0) is interpreted as the rate of energy absorption (per unit volume), since d E/d t = /)co(d AVd t) while tire quantity E dha is interpreted as the incident energy flux, which depends only on the field intensity and is independent of frequency. 

While a laser beam can be used for traditional absorption spectroscopy by measuring / and 7q, the strength of laser spectroscopy lies in more specialized experiments which often do not lend themselves to such measurements. Other techniques are connnonly used to detect the absorption of light from the laser beam. A coimnon one is to observe fluorescence excited by the laser. The total fluorescence produced is nonnally proportional to the amount of light absorbed. It can be used as a measurement of concentration to detect species present in extremely small amounts. Or a measurement of the fluorescence intensity as the laser frequency is scaimed can give an absorption spectrum. This may allow much higher resolution than is easily obtained with a traditional absorption spectrometer. In other experiments the fluorescence may be dispersed and its spectrum detennined with a traditional spectrometer. In suitable cases this could be the emission from a single electronic-vibrational-rotational level of a molecule and the experimenter can study how the spectrum varies with level. 

In a MALDl experiment, the sample is mixed or dissolved in a matrix material that has an absorption spectrum matching the laser wavelength of energy, The sample may not have a matching absorption peak (a), but this is not important because the matrix material absorbs the radiation, some of which is passed on to the dissolved sample. Neutral molecules and ions from both sample and matrix material are desorbed (b). 

Molecules and atoms interact with photons of solar radiation under certain conditions to absorb photons of light of various wavelengths. Figure 10-4 shows the absorption spectrum of NO2 as a function of the wavelength of light from 240 to 500 nm. This molecule absorbs solar radiation from... 

As long as 9 > 9, and the sample is not absorbing, the reflectivity of the prism/sample interface will be complete. However, at any wavelength where the sample is absorbing, the reflectivity will be attenuated or less than complete. Thus, an absorption spectrum that is similar to that obtained in transmission can be produced in ATR. 

Figure 12.12 An infrared absorption spectrum of ethyl alcohol. CH3CH2OH. Atransmit-tance of 100% means that all the energy is passing through the sample, whereas a lower transmittance means that some energy is being absorbed. Thus, each downward spike corresponds to an energy absorption.

Absorption spectrum (Section 12.5) A plot of wavelength of incident light versus amount of light absorbed. Organic molecules show absorption spectra in both the infrared and the ultraviolet regions of the electromagnetic spectrum. 

Absolute configuration, 299 Absorbance, 501 Absorption spectrum, 420 Acesulfame-K, structure of, 1006 sweetness of, 1005 Acetal(s), 717... 

From the color (absorption spectrum) of a complex ion, it is sometimes possible to deduce the value of AOJ the crystal field splitting energy. The situation is particularly simple in 22Ti3+, which contains only one 3d electron. Consider, for example, the Ti(H20)63+ ion, which has an intense purple color. This ion absorbs at 510 nm, in the green region. The... 

In more sophisticated instruments, the modern tendency is to replace the micro-ammeter by a digital read-out, and there is an increasing trend to use visual display units to show the results. Such instruments are controlled by microprocessors which may either show sequentially the successive operations which must be performed to measure the absorbance of a solution at a fixed wavelength or to observe the absorption spectrum of a sample alternatively the whole procedure may be automated. Such instruments will display the absorption spectrum on the VDU screen, and by linking to a printer, a permanent record is produced. 

Molecular weight. The molecular weight of C. hilgendorfii luciferase reported in the past varies considerably across a range of 50,000-80,000 (Chase and Langridge, 1960 Shimomura etal., 1961, 1969 Tsuji and Sowinski, 1961 Tsuji et al., 1974) it appears most likely to be 60,000-70,000. The luciferase is an acidic protein with an isoelectric point of 4.35 (Shimomura et al., 1961). The absorption spectrum of luciferase is that of a simple protein without any prosthetic group, showing a peak at 280 nm. Absorbance value at 280 nm of a 0.1% luciferase solution is approximately 0.96 (Shimomura etal., 1969). 

Fig. 7.1.4 Absorption spectrum of purified Chaetopterus photoprotein in 10 mM phosphate buffer, pH 6.0, containing 0.1 mM oxine and 0.2 M NaCl, measured against the buffer used. The dashed line indicates a 5-times expansion in absorbance.

If we pass white light through a vapor composed of the atoms of an element, we see its absorption spectrum, a series of dark lines on an otherwise continuous spectrum (Fig 1.11). The absorption lines have the same frequencies as the lines in the emission spectrum and suggest that an atom can absorb radiation only of those same frequencies. Absorption spectra are used by astronomers to identify elements in the outer layers of stars. 

Visible and ultraviolet absorption spectra are measured in an absorption spectrometer. The source gives out intense visible light or ultraviolet radiation. The wavelengths can be selected with a glass prism for visible light and with a quartz prism or a diffraction grating for ultraviolet radiation (which is absorbed by glass). A typical absorption spectrum, that of... 

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