Quenching collisions

The detection of O( D) by the emission at 6300 A would be extremely difficult because the emission life is about 150 sec (32). Even at a pressure of 1 mtorr of 03 each O( D) atom would undergo about 106 collisions with O, molecules during its lifetime. Consequently, the emission intensity would be reduced by a million times by collision quenching. In spite of the difficulties, Gilpin ct al. (398) have succeeded in following the decay of the extremely... 

Electron-transfer process has been observed between fluorophore and metal surface by photocurrent measurement [9, 29, 30]. Transient absorption studies have shown the charge separation between the dye molecule and gold nanoparticies upon pulse laser excitation [31]. In the collision quenching process, the nonradiative rate is proportional to the quencher concentration [19]. 

V.K.Bykhovski and E.E.Nikitin, Nonadiabatic transitions in atomic collisions. Quenching of sodium resonance fluorescence by aigon, Optika i Spektr. 17, 815 (1964)... 

The fate of the excitation energy depends on the nature of the molecule and on the amount of energy is receives. The excited molecule may give off the energy as radiation (fluorescence), dissipate it by collisions (quenching), utilize the energy for chemical transformations (isomerization, dissociation, ionization, etc.), transfer all or part of the energy to other molecules that then react further (sensitization), or enter into chemical reactions directly. Several of these processes are written in Table 2-4 in the form of chemical reactions. They are considered primary processes in the sense that they all involve the excited molecule formed initially by photon absorption. 

The extent of collision quenching is very sensitive to solvent viscosity, and also depends on temperature. Additionally, the unquenched [Ru(Ph2phn)3] lifetime in propanol decreases from 52 /cs at 20 to 2.9 fts at 50 "C which results in decreased phase angle from 813 to 76.4 degrees at 03 MHz. This is a modest effect compared to the almost 70 degree change due to oiygen partial pressure from 0 to 200 mm Hg. Hence, temperature effects are simple to correct for, and in fact the unquenched lifetimes of other Ru(II) complexes can be used to measure the temperature (30,58, Lakowicz, J.R. Szmadnsld, H. unpublished observation). 

Fluorescence quenching and NRET belong to popular fluorescence variants that have been exploited in a number of fields, including polymer and biopolymer research. NRET has been used in studies of polymer chain conformations [64-68], polymer miscibility [69-71], etc. Collision quenching, which reflects the accessibility of different quenchers, has been applied for testing the environment of pendant quenchers in polymer and biopolymer structures and associates [72-74]. Because the measurement is relatively simple, both techniques are benchmark fluorescence techniques in polymer science. Therefore, we could not avoid their use and, in spite of a number of review articles on that subject, we will briefly outline our results aimed at polymer self-assembly. 

The effective lifetime of an excited molecular level is tesip = 5 mbar) = 8 X 10" s and Tesip = 1 mbar) = 12 x 10" s for molecules with the mass M = 43 AMU in a gas cell with argon buffer gas at T = 500 K. Calculate the radiative lifetime, the collision-quenching cross section, and the homogeneous linewidth Av( >). 

To demonstrate the calculation of the collision quenching (or transfer) cross section, let us consider the case of singlet-singlet quenching given by Eq. (70). Making use of the Bethe integral (Mott and Massey, 1965),... 

An early model for the correlation of collision quenching data was due to Rossler (1935) interaction is assumed to be proportional to the polarizability a of the quenching molecules and the duration of the collision (i.e., where /i is the reduced mass). It predicts that the quenching cross section vs. 

The fluorescence resonance energy transfer (FRET), also called noiuadiative excitation energy transfer (NRET) or direct energy transfer (DET), is one of the processes that quench the fluorescence of an excited fluorophore. In contrast to collision quenching, the excitation energy of the donor is transferred to another molecule (acceptor) over nanometer distances and the underlying mechanism does... 

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