Cationic absorption

Toxicity is found to be low and related only to the neuromuscular blocking effects. Provided that artificial ventilation is available. 10,000 times the normal effective dose evinces no acute toxicity in anaesthetized cats for up to two hours after injection.asusual. species vary in susceptibility to toxic effects. As might be expected of a higlily-charged cation, absorption from the gut is poor. No hormonal effects have been detected. 

Deussen M, Bassler H (1993) Anion and cation absorption-spectra of conjugated oligomers... 

CrflII) complexes of the type [(H20)5CrR]2+ have been widely investigated in solution (57). These orange-colored cations, absorption maxima —400 (—300), —280 (—300), —555 (-25), have a solution stability that is quite dependent on R and undergo a variety of reactions includ-... 

Fig. 1. Rise of the perylene cation absorption, which reflects the electron injection dynamics, after excitation of the first singlet state with a 15 fs pump pulse. Variation of the electronic coupling via a change in the anchor group as well as the insertion of one or two -CH2- groups leads to a systematic change in the time scale of both electron injection and charge recombination.

Fig. 2. Transient absorption of Pe -Tripod probed at 570 nm (squares). The measured signals a superposition of cation absorption and stimulated emission (negative signal). The data were fitted to a three-exponential rise (solid line) revealing time constants of 30 fs (42%), 720 fs (33%) and 4.3 ps (25%). The inset illustrates the atomic structure of the Pe -Tripod and its LUMO state, both calculated on a semi-empirical level.

Initiation of tetrahydrofuran polymerisation by Ph C SbClg has been studied speetrophotometrieally by Ledwith and co-workers (20). Decay of the characteristic triphenylmethyl cation absorption, in methylene chloride was represented by the expression... 

The first chelating resins that were found to be really suitable for application in the field of selective cation absorption were those based on the aminodiacetate functional group.380 The first commercial resin based on this functional group, Dowex Al, was shown381 to have an affinity for a range of metals which was similar to the order of dissociation constants of the metal complexes with ethylenediaminetetraacetic acid (EDTA), i.e. 

However, the initial step of the electron transfer reaction strongly depends on the solvent polarity. By changing the solvent to less polar or nonpolar solvents like benzene or nonaromatic hydrocarbons the transient absorptions of 3C 0, G)0 and donor radical cation appear immediately after the laser pulse. The decay of all the absorptions is also completed at the same time. The fast appearance and the fast decay of the Go and donor radical cation absorption suggest that there is an interaction between fullerene and donor in less polar and nonpolar solvents before laser irradiation [120,125,133-139],... 

A molecular ion-dominant spectrum has been observed for 2,3-dimethyl-1,3-butadiene (DB) excited with a 1.4-pm and 130 fs pulse, as shown in Fig. 2.5a, whereas many fragment ions were produced with a 0.8-pm femtosecond pulse of the same pulse width and intensity as shown in Fig. 2.5b. The cation absorption spectrum shown in Fig. 2.5c revealed that the non-resonant conditions hold with an excitation wavelength of 1.4 pm [4]. 

Anthracene was irradiated with femtosecond pulses and heavy fragmentation was observed at 0.8 pm [5,6] however, singly, doubly, and triply charged molecular ions were dominant at 1.4 pm [11]. The cation absorption of anthracene indicates that 0.8 pm is resonant and 1.4 pm is non-resonant with the electronic levels as shown in Fig. 2.6. 

Fig. 2.6. a TOF mass spectra of anthracene at 1.4- and 0.8-p.m excitations, and b the cation absorption spectrum in a low-temperature matrix with two spectra of the excitation pulses... 

Cgo has been ionized by pulses from 5 ps to 25 fs the shortest pulse of 25 fs produced Cqq (z = 1,2) without heavy fragmentation [20] at 0.79 pm. Very recently, Hertel and coworkers detected a single peak of the singly charged ions [21], where they irradiated C60 with a 9-fs pulse at 0.8 pm. It should be noted that this wavelength is resonant with the cation electronic level. From the above results, it may be considered that with sub ten fs pulse, intact molecular ion formation is possible for any molecule, even if the excitation wavelength is resonant with the cation absorption levels. 

Therefore, a molecule in the TICT state can be regarded as a rigidly linked radical anion-radical cation pair. Experimental proof for this expectation can be gained from transient absorption spectroscopy. In the simplest case, the absorption spectrum of the TICT excited state is expected to be the sum of the individual ion spectra. This was indeed found in a few cases, with some perturbations which can be explained by the interaction of the closely-spaced radical ions. Thus, the transient absorption spectra of DMABN [135], of DMABK (or DMABA) [137] and of BA [58] resemble the spectrum of benzonitrile and acetophenone radical anion (the absorption of the dimethyl-amino radical cation is expected to be situated in the UV region and could not be observed) and to the sum of anthracene anion and cation absorption spectra, respectively. 

When initiation is more complex, the elementary reactions can sometimes be studied separately. This is the case for initiation of the polymerization of 1,3-diox-olane with trityl salts. In the first reaction, hydride transfer takes place and then the newly formed cation reacts again with monomer. This second process is considerably slower than the former one. The first hydride abstraction was studied by (disappearance of the trityl cation absorption at X = 430 nm, Cmax =" 3-6 10 ) and by polarography (observation of (C6H5)3C giving a reversible one-electron wave for the trityl ion reduction with Eyz 0.51 V). 

The decay of the carotenoid radical cation absorption of C +-P-C6o occurs on the micro second time scale in the frozen glass. It is accompanied by the rise of C-P-Ceo generated by charge recombination of the C -P-Ceo biradical, which is formed with a quantum yield of 0.07. The major component of the decay of the - C-P-Ceo transient has a time constant of 10 ps, which is a typical lifetime for a carotenoid triplet state. The absorption of C -P-Ceo " at 77 K does not decay exponentially, but an average decay rate of 7.5 x 10 s may be calculated from the data [155]. Time-resolved experiments have allowed detection of the EPR resonances of the C +-P-C6o biradical and C-P-Ceo- The spin-polarization of the carotenoid triplet spectrum verifies formation of this state by the radical pair... 

Results and Discussion. The scattering patterns of the NiSPS sample, taken 5 and 100 eV below the measured cation absorption edge, are shown in Figure 5. The constant shift due to fluorescence is apparent by looking at the difference between the two curves on either side of the ionomer peak. Once this component is subtracted. 

When biphenyl was added to polyethylene [174], the biphenyl anion and cation absorption spectra were obtained after irradiation, together with an apparently unchanged trapped-electron absorption. QJ and Qj were both removed by photobleaching. On warming, Qj starts to decay at —120°C, the temperature which corresponds to the first transition in polyethylene. This suggests that the decay is due to diffusion and reaction of the Q2 ion rather than to thermal ejection of the attached electron. 

In the continuation of our work a study has also been made of the system benzene/silica gel. When irradiating this system at 77 °K. it was found that the silica gel could stabilize both monomeric and dimeric cation radicals of benzene (6). Furthermore, the high resolution of the electron spin resonance lines indicated a high degree of mobility for the benzene molecules in the adsorbed layer. No spectrum from trapped electrons could be observed although this could very well be hidden behind the strong cation absorption. However, ethylene, and isobutylene in the adsorbed state at low temperature gave spectra from shortlived species identified as trapped electrons (7). 

An examination of Fig. 4 shows that the stabilization results in a decrease in anion-absorptive capacity and no change in the cation-absorptive capacity. This means a net increase in the cation-exchange capacity. 

If small amounts of H ion are assumed to be present in all solutions, the basic nature of the anion absorption curve will remain unchanged. The cation absorption curve will only parallel the anion absorption curve for large salt concentrations and will go through the origin. The simple picture just outlined is thus capable of accounting qualitatively for all features of Fig. 4 that do not arise from the instability of the fiber. 

Effect of Temperature. The effect of temperature on Na and SO4 absorption is shown in Fig. 5. Temperature coefficients for equilibrium absorption cannot be determined until possible complications resulting from instability are removed. However, the temperature coefficient for cation absorption is certainly small and that for anion absorption would be anticipated to be small also. All in all there is no evidence for any appreciable heat change during the absorption process. 

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