Volume 115, Issue 21, 01 December 2001
Index of content:
115(2001); http://dx.doi.org/10.1063/1.1421382View Description Hide Description
The influence of oxygen on the photophysical properties of individual molecules has been investigated by means of both wide field and confocal scanning optical fluorescence microscopy. Excited close to saturation intensity, single-molecule fluorescence detected in wide field by a charge-coupled devicecamera showed a dramatic increase at exposure to air compared to the fluorescence when the sample was protected from oxygen by nitrogen flush. The change of the triplet lifetime of individual dye molecules due to oxygen quenching was measured in real time by means of time resolved single photon counting. In the presence of oxygen, the triplet state lifetime decreases from several tens of milliseconds down to fractions of a millisecond, whereas no changes of the intersystem crossing quantum yield and the fluorescence lifetime are observed. The triplet lifetimes in the presence and absence of oxygen, respectively, are anti-correlated indicative of heterogeneity of the polymer surrounding the dye molecules.
115(2001); http://dx.doi.org/10.1063/1.1423945View Description Hide Description
Photodissociationdynamics of benzene under 193 nm and 157 nm photon excitation have been studied using the molecular beam photofragmentation spectroscopic technique. By detecting the H atom products produced away from the photolysis region, the lifetime of the excited benzene molecule as well as the kinetic energy distribution of the H atom elimination process can be determined simultaneously. Experimental results show that the H atom elimination from benzene occurs on the ground electronic state in which the excess energy is likely fully randomized.