Near-infrared absorption band

Let us close this paragraph with MMCT transitions between two ions of the same element, one with the other with d configuration. Jorgensen [56] showed long ago that the simultaneous presence in 12 M hydrochloric acid of pale yellow Ti(IV) and blue Ti(III) yields a dark brownish-purple 1 1 complex with a stronger absorption band than the single constituents have. The broad absorption band has a maximum at 482 nm. The new absorption band is ascribed to a Ti(III)-Ti(IV) MMCT transition. A near-infrared absorption band in titanium-doped AI2O3 seems to be due to the same transition [57]. 

In addition, near infrared absorption bands at 1.255 and 1.425 /tm have recently been found by Hunziker and Wendt (493), who have attributed the bands to a transition 2 A <- 2A". The band at 1.504 /emission bands of H02 have been detected recently by Becker et al. (83, 86). The H02 radical is an important reaction intermediate in combustion, in polluted atmospheres, and in the photolysis of H202. The reaction of H02 with NO is considered as a key reaction in photochemical smog formation, which is discussed in Section VIII 2. 

Examples of useful near-infrared absorption bands... 

Bokobza, L. (2002). Origin of near-infrared absorption bands. In Near-Infrared Spectroscopy Principles, Instruments, Applications, Siesler, H. W., Ozaki, Y., Kawata, S., and Heise, H. M., eds., Wiley-VCH, Weinheim, Germany, pp. 11-39. 

Individual near-infrared absorption bands have absorptivities on the order of 10 1 Al /mm/mM for peak absorption bands in aqueous matrices.30 Such low absorptivities limit detection to the major components within skin tissue. As a general rule of thumb, substances must be present at concentrations above 1 mM to be quantified by near-infrared spectroscopy. Although such low absorptivities greatly restrict the number of possible analytes one can measure in clinical samples, the inability to measure chemicals present below millimolar concentrations enhances selectivity by rendering measurements insensitive to many different types of endogenous molecules. Only the major chemical components of these biological samples must be considered for selectivity purposes. 

Wharton, D. C., and Tzagoloff, A., 1964, Studies on the electron transfer system LVll. The near infrared absorption band of cytochrome oxidase, J. Biol. Chem. 239 203692041. 

The copper(I) alkynyls displayed rich photochemistry and particularly strong photoreducing properties. The transient absorption difference spectrum of [Cu3(dppm)3(/X3-) -C=CPh)2]+ and the electron acceptor 4-(methoxycarbonyl)-A-methylpyridinium ion showed an intense characteristic pyridinyl radical absorption band at ca. 400 nm. An additional broad near-infrared absorption band was also observed and it was assigned as an intervalence-transfer transition of the mixed-valence transient species [Cu Cu Cu (dppm)3(/x3- -C=CPh)2] +. The interesting photophysical and photochemical properties of other copper(I) alkynyl complexes such as [Cu(BTA)(hfac)], 2 [Cui6(hfac)8(C=C Bu)8], and [Cn2o(hfac)8(CsCCH2Ph)i2] have also been studied. 

Various broadband sources employed to optically pump Ha include tungsten, mercury, xenon, and krypton lamps. The last source provides an especially good spectral match to the near-infrared absorption bands of Nd3+ in YAG. To reduce lattice heating resulting from the multiphonon emission decay to the F3/2 state, semiconductor diodes and laser sources at 0.8-0.9 ym nave pumped Nd lasers (58). Sun-pumped Nd and chromium-sensitized Nd lasers have been demonstrated and considered for space applications (59). Lasing of Nd3+ by electron beam excitation has also been reported (bO). 

While the majority of the studies of carotenoid radicals have been based on monitoring the strong near infrared absorption bands, other techniques, including time resolved resonance Raman spectroscopy (Jeevarajan et al., 1996), FTIR spectroscopy (Noguchi et al, 1994), EPR (Grant et al., 1988), ENDOR (Piekarasady et al., 1995), and cyclic voltametry (Grant et al, 1988) have also been used. 

Reaction of Stable Solvated Electrons with Water. One of the most promising ways of generating a homogeneous solution of hydrated electrons has been pursued by Dewald, Dye, Eigen, and DeMaeyer (26), who mixed a solution of electrons solvated in ethylenediamine with water. These authors took a solution of Cs in ethylenediamine, a solvent in which solvated electrons are stable, and combined it in a fast-flow mixing cell with a solution of water in ethylenediamine. They then followed the rate of decay of the near infrared absorption band of e ed as a function of water concentration. More recently other active metals have been used and the kinetics fully analyzed (32). The second-order rate constant (20M 1 sec. 1) obtained is attributed to Reaction 16 and compared with... 

Fundamental vibrational transitions, namely between the ground state and first excited state, take place in the mid-infrared, while in the region of near-infrared absorption bands are due to transitions between the ground state and the second or the third excited state. This type of transitions are called overtones and their absorption bands are generally very weak. The absorption bands associated with overtones can be identified and correlated to the corresponding absorption bands arising from the fundamental vibrational transitions because they fall at multiple wavelengths of these. 

Many near-infrared absorption bands occur with sufficient regularity to allow the characterization of certain molecular groups, just as is done with fundamental bands in the 3-15 /r range. 

The analysis of water in various media and under various conditions has been a major part of the field of near-infrared (IR) spectroscopy since its inception. The strength of the near-infrared absorption bands, the unique water combination band at 1940 nm, and the sensitivity of the absorption bands to the environment of the water molecules have all contributed to the success of near-infrared to smdy and measure water. 

H. Mark, Chemical Assignments of Near Infrared Absorption Bands, Customer Applications Group, Technicon, Tarrytown, NY. 

Near-infrared absorption bands are so weak that vapor phase work in this region has little value. 

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