Absorption spectroscopy strengths

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. 

Fontaine, A., Dartyge, E., Itie, J. P., Juchs, A., Polian, A., Tolentino, H. and Tourillon, G. Time-Resolved X-Ray Absorption Spectroscopy Using an Energy Dispensive Optics Strengths and Limitations. 151, 179-203 (1989). 

Once the FBA has been identified, ultraviolet absorption spectroscopy affords a rapid and accurate method of quantitative analysis. Care must be taken when interpreting the spectra of stilbene-type compounds, since turns to cis isomerisation is promoted by ultraviolet radiation. Usually, however, a control spectrum of the turns isomer can be obtained before the compound undergoes any analytically significant isomerisation. FBAs are often marketed on the basis of strength comparisons determined by ultraviolet spectroscopy. 

The very weak Tm - So transitions are hard to observe directly by absorption spectroscopy. Even with long cells, the high concentrations required present solubility — and what is more important — purity problems. An impurity of 1 10 may give rise to absorption bands which have the same intensity as the expected Ti So absorption. The experimental conditions, therefore, have to be chosen to allow an increase of the Ti- - So oscillator strength to be achieved through perturbation by paramagnetic species (O2 or NO) or heavy atoms. Alternatively, an indirect method, phosphorescence excitation spectroscopy, which has high sensitivity and selectivity, may be applied. 

With the development of intense synchrotron X-ray sources, it has become possible to use X-ray absorption spectroscopy to structurally characterize the metal clusters in metalloproteins. A wide variety of systems have been studied in this manner in the last ten years. The present article reviews the nature of X-ray absorption spwtroscopy and the information which can be obtain fix)m its study. The strengths and Kmitations of the technique are discussed with reference to the recent literature. 

The cross section a is a fundamental property of the molecule and as such is related to the molecular wave functions for the two states between which a transition is induced. Hence it is desirable to separate the contributions to a that arise from purely kinematic quantities such as the impact energy of the electron beam from those that depend solely on the properties of the molecule. To this end, a dimensionless quantity, the oscillator strength, is introduced in optical absorption spectroscopy, defined by the relation22... 

The high molecular specificity of Raman spectra results in less spectral overlap than other modalities such as NIR absorption spectroscopy, thus enabling the detection of low signal strength components such as glucose. 

The solubility of silver sulfadiazine has been determined by equilibrating the compound in doubly distilled water at 25 C and the measurements of the saturated solution for sulfadiazine by UV spectrometry and for silver by atomic absorption spectroscopy (7). Nesbitt and Sandmann (22) measured the equilibrated solution for silver using a silver-ion selective electrode. Their measurements were performed at 25°C in nitric acid -potassium nitrate buffers (pH 2-3) and ionic strength 0.1. 

---