Singlet optical processes

An analysis of the calculated transition dipole moments of the APSS molecule shows that only transitions between the singlet Sq, Sj and S, states dominate in the nonlinear optical process of interest (see Fig. 2) and we therefore restricted our simulations to comprise these three states. To explain the observed delay between the ASE and pump pulses, we need to take into account the vibrational structure. We model this structure for the levels Sj and Sq by including two pairs of vibrational levels, (4, 3) and (2, 1), respectively, making use of the one-mode approximation. The vibrational levels 3 and 1 are the lowest vibrational states for the electronic states Sj and Sq, respectively (Fig. 2). The vibrational state 4 models the group of vibrational states nearby the vertical photoabsorption transition Sq -> Sp Apparently, the vertical transition has larger probability. The lasing transition takes place from the vibrational level 3 to the vibrational level 2 which corresponds to the vertical decay Si -> So (Fig. 2). The transition matrix element is a product of the electronic matrix element and the Franck-Condon amplitude between vibrational states v and t ... 

In addition to heat emission, radiative decay processes may also occur, in which light is emitted due to a transition from the lowest excited singlet or triplet state to the ground state (fluorescence or phosphorescence). In order to effect rapid and efficient conversion of optical energy (the laser) to heat, dyes which exhibit low fluorescence and in which excitation primarily involves the singlet states are the most suitable for heat-mode recording.196... 

When formaldehyde is subjected to suitable optical excitation it dissociates into H2 and CO. The process is thought to involve an excitation to the first excited singlet state followed by internal conversion to a highly excited vibrational state of the ground singlet state that dissociates according to the equation... 

The sky emits radiation, known as the airglow, which during both day and night contains components resulting from optical transitions of O Ag) and 02(1Se+), and it is important to assess the possible mechanisms by which Oa may be excited to see whether they can account for the observed concentrations of singlet 02. The concentrations of possible precursors, such as 0(3P), (X1/)), and 03, probably undergo a diurnal and a seasonal variation, and it should be possible to relate the changes in [O2(1A0)] and [02(1E J+)] to the rates of excitation and loss processes. Several problems arise in these studies, since, for many of the potentially... 

Recently, the primary processes were investigated using pulse radiolysis with two extractant-alkane systems (182, 292). Transient optical absorption spectra proved that in the presence of ligands like TODGA, the excited species of -dodecane (singlet excited state and radical cation) disappeared immediately. Results showed that an energy transfer occurred from the excited alkane to the extractant molecule (TBP, TOPO, or amide), which constituted an additional decomposition route, as described in the following set of reactions ... 

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