Absorption spectroscopy, lead compounds

MDHS6 Lead and inorganic compounds of lead in air (atomic absorption spectroscopy). 

Fortunately, this requires no additional investment (apart from a UV-vis spectrometer that is, however, available anyway in most laboratories), because highly polished salt (KBr or Csl) windows are sufficiently transparent down to 200 nm so that high-quality UV-vis spectra can be obtained with the exact same sample configuration as is used for IR absorption spectroscopy. As in IR spectroscopy, it is often useful to look at difference spectra, but as bands due to different compounds have much more of a tendency to overlap in this case, which may lead to distortions in the difference spectra, one has to be cautious in assigning band maxima from difference spectra. 

The absorption spectrum of 22 is nearly identical to the sum of the spectra of unlinked model compounds. The long wavelength band of the free base porphyrin is observed at 650nm in chloroform, whereas that of the zinc porphyrin is at 590nm. Excitation of a chloroform solution of 22 with a 15 ns pulse of 650 nm laser light leads to the formation of a carotenoid radical cation which can be detected by transient absorption spectroscopy (Figure 14). This ion arises from the charge separated state C -Pzh-P-Qa-Qb, and is formed with a quantum yield of 0.83. The lifetime of the species is 55/iS. 

On the basis of product studies, it is clear that irradiation of the naphthyl azides leads to loss of nitrogen with the likely consequent formation of nitrenes. Just as for phenyl azide, the initially formed singlet nitrenes may intersystem cross to the triplet and then dimerize to azo compounds. Clearly in the case of 2-naphthyl azide, but not 1-naphthyl azide, a closed-shell ground-state intermediate that can be trapped with diethylamine can be generated. The intermediate was formulated as the azirine on the basis of product studies [57]. Low temperature absorption spectroscopy and time-resolved laser flash photolysis experiments to be described later support the formation of azirines and provide an explanation for the different reactivity observed between the 1- and 2-substituted azides. 

Robinson, J.W. and Boothe. E.D. (1984). Speciation of Organo Lead Compounds by TLC and High Performance Chromatography - Atomic Absorption Spectroscopy Decomposition of TEL. In Sea Water. Spectrosc. Lett. 17, 689. 

Lead is not spectroscopically silent. The absorption spectroscopy, photoelectron spectroscopy, and NMR spectroscopy of Pb(II) compounds have all been extensively studied. These techniques not only provide useful insights into the electronic structure and stmctures of Pb(II) compounds, but have also proven useful in the characterization of lead coordination environments in complex samples (e.g., samples of biological or environmental origin). 

Pingitore NE Jr, Glague J, Amaya MA, Maciejewska B, Reynoso JJ (2009) Urban airborne lead X-ray absorption spectroscopy establishes soil as dominant source. PLoS One 4 e5019 Rasmussen PE (2004a) Elements and their compounds in indoor environments. In Merian E, Anke M, Dinat M et al (eds) Elements and their compounds in the environment. Wiley, Germany, pp 215-234... 

The generation and behaviour in acid media of the radical cations of aromatic compounds investigated by ESR and absorption spectroscopy in the UV and visible regions do not allow us to draw unequivocal conclusions for the role of similar particles in the formation and conversions of arenium ions and hence for electrophilic aromatic substitutions. At a certain ratio of energetic levels the interaction of ArH and X" may be accompanied by the formation of the radical pair [ArH", X"] which is in equilibrium with the free radical ArH" and X , the binding of the X radicals leading to accumulation in the system of the ArH radical cation. It remains unclear, however, whether the formation and recombination of the radicals ArH" - and X (route b, c) may be more favourable than the direct route (a) of a-complex formation. 

Core-level spectroscopies are the appropriate tools to study the electronic distribution around free atoms and the changes induced in this distribution on condensation or on the formation of compounds involving other elements. These spectroscopies are also very useful to track the formation of clusters which finally coalesce to form well-defined solid phases. For the R, X-ray absorption spectroscopy is very useful because of the simplicity of the final multiplet structure, as the transitions obey dipole selection rules. Generally, two types of transitions are observed one in which the 4f electron participates in the transition and another in which it remains as a spectator. In the former case, a transition of a d electron to the empty f shell is involved. This leads to the formation of the nd 4f - d 4f + ( = 3,4) multiplets which are in fact finger prints of the R atom configurations. In the same way, the transitions from p levels scan the empty sd states of the conduction band. 

Robinson, J. W., Boothe, E. D., Speciation of Organo Lead Compounds by T.L.C. and High Performance Liquid Chromatography-Atomic Absorption Spectroscopy. Decomposition of TEL in Sea Water, Spectrosc. Letters 17 [1984] 689/712. 

Towards this goal, there have been extensive studies that have compared PTR-MS measurements of atmospheric VOCs with those obtained by other atmospheric analytical techniques, such as GC-MS [17], GC-FID [21-26], atmospheric pressure chemical ionization mass spectrometry (AP-CIMS) [27], differential optical absorption spectroscopy (DOAS) [24,28] and Fourier transform infrared (FTIR) spectroscopy [17,29], in addition to offline sampling methods coupled to GC analysis [30-34], These studies have shown that PTR-MS is capable of accurately measuring concentrations of VOCs providing that there is no contribution to the miz of interest in a mass spectram by interfering species. If other compounds are present in the atmospheric sample which can lead to ions (protonated parent compounds, cluster ions or fragment ion species) at the nominal mJz of the protonated VOC of interest, then the lack of specificity associated with PTR-MS requires that the actual identity of the compound still needs to be confirmed by other analytical techniques, such as GC-MS. 

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