Life-time, excited state radiative

Fig. 11 Normalized time and frequency resolved emission spectrum of the CC P4. A 6 ps time averaging has been carried out to mimic the apparatus function of the single photon detector. Radiative and non-radiative decay has been accounted for by a common chromophore excited-state life time of 5 ns.

If the excited level contains e2 states hv above the groundstate (representing e( mutually orthogonal states), Einstein s formula from 191733 relates the radiative life-time rrad to the oscillator strength P of absorption ... 

Figure 1. Schematic energy level diagram of an organic dye molecule illustrating radiative (full line) and radiationless transitions (dotted line). S0 and. S, are the electronic ground and excited states, T, is the triplet state and /cjsc is the intersystem crossing rate, t, and t3 are the life times of the states S, and Tj, respectively.

The extremely narrowband emission of a laser allows the specific excitation of molecular states. The non-Boltzmann distribution produced by the excitation process is quickly destroyed by radiation processes and collisional deactivation. The relative contribution of these different deactivation channels depends on the nature of the level excited as shown in Fig. 3. In the microwave region where rotational levels are excited, the radiative life time is very long compared to the very efficient rotational relaxation processes (R—R rotation—rotation transfer and R—T rotation—translation transfer). Therefore, the absorbed radiation energy is transformed within a few gas kinetic collisions into translational energy. The situation is similar for... 

Low-lying electronically-excited Ag and states of O2, which are metastable with respect to transitions to the ground state, are well known. These species not only have very long radiative life times ( 10 s for 4000 s for but also electronic quenching is... 

In the cases of N2 and CO, which possess large dissociation energies, no dissociation occurs on impact with Ar, but energy transfer from Ar causes extensive electronic excitation. The steady state distributions of energy in both N2 and CO excited by Ar have been investigated in detail. In the case of the most fully allowed transitions observed, little or no rotational (or vibrational) relaxation is expected to occur within the radiative life-time at a pressure of 0 5 torr. In such a case, the observed energy distribution is that initially imparted to the substrate molecule by impact with Ar. In some cases, study of the dependence of rotational energy distribution upon total pressure also enables rates of rotational relaxation to be derived an example is the C n state of N2. ... 

Upon addition ofTi02 nanoparticles, the fluorescence intensity of courmain-343 was quenched and a new, red-shifted, emission band developed. The fluorescence decay could be fitted to a multi-exponential fimction, with life times of 190 ps (82%), 1.8 ns (6%) and 4.4 ns (12%). The first two components were attributed to radiative back electron transfer from the nanoparticles to strongly and weakly coupled compounds. The 4.4 ns lifetime was assigned to courmain-343 excited states that did not inject electrons into the conduction band. It was noted that the dynamics of the back electron transfer, measured by... 

---