Weak narrow bands

Karraker measured the electronic absorption spectrum of dimeric uranium penta-ethoxide and the weak narrow bands observed at 5405, 5680, 6622, 6934, 10200, 11 690, and 14 490 cm" have been assigned to f-f transitions for a distorted octahedral f system with a spin-orbit coupling constant of 1905 cm. ... 

The sample dissolved in a weak (nonpolar for siliea gel), volatile solvent is applied as a narrow band across the plate. Manual applieation can be aehieved with a pipet or syringe gnided by a ruler, or roimd spots ean be placed close together, side by side, in a line. Sample applieation instruments are available commercially, e.g., a meehan-ical streaker from Analtech and an antomated spray-on apparatus from CAMAG. 

This hypothesis was supported by analysis of the transient spectrum obtained upon LFP of 2-fluorophenyl azide, which reveals the presence of triplet nitrene 20a despite the small ratio of kisc/koss- This is clearly evident in Fig. 16 (Insert Spectrum 1), which presents the spectrum of the products formed from the decay of singlet nitrene 16a at room temperature. This spectrum is the sum of the spectrum of triplet nitrene 20a (narrow band at 303 nm and weak absorption below 450 nm) and ketenimine 18a (broad band at 350 nm). This complicated spectrum can be eompared with the simpler spectrum of ketenimine 18b (Spectrum 2) and the spectrum of triplet nitrene 20a observed as a persistent species in a low-temperature matrix (Spectrum 3). It is clear that the yield of triplet nitrene 20a is significant at room temperature. However, if one postulates that azirine 17a does not inter-eonvert with singlet nitrene 16a (Scheme 6, -r). then the yield of... 

Once the detector has been chosen, the problem remains of demonstrating that any radiation observed is that of the oxygen systems, and of separating the bands from each other and from any background radiation. For the 7620 A band it is possible to use a spectrograph with photographic detection (as, for example, in the study of Clyne et al.27), while a monochromator may be used with photoelectric devices as exemplified by the experiments of Whitlow and Findlay.15 In many cases, however, the intensity of emission is too weak to be detected after dispersion, and narrow-band interference filters can then be used to advantage. 

The principal spectral feature of the /-state of Pseudocyanine is the bathochromic band which, depending on the substrate, absorbs between 568-582 n.m. with an extinction coefficient of 0.5-2.3 X 105M 1 cm."1 and a half-width of less than 50 cm."1. These values are in rough agreement with those obtained in aqueous gels of Pseudocyanine at concentrations above 0.1M (12). In addition to this intense and narrow band, the /-state also contains components which absorb weakly at shorter wave-... 

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