Spectrum decay

Sub-picosecond photoinduced absorption studies were employed to demonstrate the speed of the photoinduced electron transfer. Upon addition of C(M to P30T, the P1A spectrum, decay kinetics, and intensity dependence all change dramatically 36J. Already at 1 ps after photoexcitation by a 100 fs pump pulse at... 

The integrated intensity of the satellite spectrum is very close to that of the trapped electron spectrum. The former spectrum decays concomitantly with the latter either with photo-bleaching with the infrared... 

F. Barocchi, R. Vallauri, and M. Zoppi. Collision induced spectrum decay constant for Lennard-Jones interaction potential. Phys. Lett. A, 50 451-452 (1975). 

On the other hand, Rafikov et al. 112) observed a singlet and a triplet spectrum (1 2 1) after irradiation of polycaproamide at -196° C. After the sample was warmed, the triplet spectrum changed into a quintet spectrum (1 4 6 4 1). On further warming this quintet spectrum decayed out and only the singlet spectrum remained. The triplet spectrum was attributed to —CH2—CH2—CO, and the quintet spectrum to —CH2—CH2 produced by dissociation of CO from—CH2—CH2—CO. 

The former spectrum decayed after treatment at -78° C for 30 sec. Effect of oxygen on radical formation with the light of 300 nm was also reported (67). 

The dominant contribution to the full spectral density at large k comes from wavepackets whose spectrum decays most slowly in the k —> oo limit, hence... 

Nanosecond Flash Photolysis Measurements.—A computer-controlled ns flash photolysis spectrometer has been described. " The system was employed in a study of the photochemistry of xanthene dyes in solution. A nitrogen laser was used to provide 2—3 mJ excitation pulses at 337.1 nm for a ns flash photolysis study of electron-transfer reactions of phenolate ions with aromatic carbonyl triplets. " A PDP II computer was used to control the transient digitizer employed for detection, and to subsequently process the data. A nanosecond transient absorption spectrophotometer has been constructed using a tunable dye laser in a pulse-probe conflguration with up to 100 ns probe delayA method for reconstructing the time-resolved transient absorption was discussed and results presented for anthracene in acetonitrile solution. The time-resolution of ns flash photolysis may be greatly increased by consideration of the integral under the transient absorption spectrum. Decay times comparable to or shorter than the excitation flash may be determined by this method. 

Model four-stage electron transfer chains have been observed (8) using either isopropyl alcohol radicals (or ethyl alcohol), aceto and benzophenone, and, in addition, a very low concentration of ferricyanide ion. One alkaline N20-saturated solution contained 0.5M isopropyl alcohol, 2.5 X 10"8M acetophenone, 10"4M benzophenone, and 8 pM ferricyanide ion. Electron transfer from the alcohol radical ion to acetophenone, followed by transfer to benzophenone, was observed, as expected. However, the benzophenone anion spectrum decayed exponentially. The transmission of the solution, over the spectral region of the ferricyanide absorption (4100 A. maximum) increased, indicating the consumption of this solute. The kinetics of ferricyanide decay were similar to those for decay of the benzophenone ketyl absorption. The... 

Lipid vesicles containing phosphatidyl choline (95%) and the spin-labeled analog (5%) were prepared by sonication and purified by gel-filtration chromatography. The outside diameter of these liposomes was about 25 nm. The amplitude of the paramagnetic resonance spectrum decreased to 35% of its initial value within a few minutes of the addition of ascorbate. There was no detectable change in the spectrum within a few minutes after the addition of a second aliquot of ascorbate. However, the amplitude of the residual spectrum decayed exponentially with a half-time of 6.5 hours. How would you interpret these changes in the amplitude of the paramagnetic spectrum ... 

T is constant for a given electronic system but on the other hand, varies from spectrum to spectrum and could conceivably change during a single measurement as a short-lived component of the spectrum decayed. 

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