Physical Chemistry 3: — Chemical Kinetics — - Christian-Albrechts ...

11.6 References 241
12. Photochemical reactions
I
Primary photochemical processes:
• Absorption of a photon (depends on transition dipole moment ¯¯ ¯¯2),
• Intramolecular processes:
— fluorescence (≡ spontaneous emission of a photon, FL),
— stimulated emission (SE), (⇒ Einstein coefficients)
— chemical reaction in the excited state (R),
— intramolecular vibrational (energy) redistribution (IVR),
— internal conversion (IC),
— intersystem crossing (ISC),
— phosphorescence (PHOS).
• Intermolecular (i.e., collisional) processes:
— electronic deactivation (quenching, Q),
∗ may affect fluorescence as well as phosphorescence,
— vibrational energy transfer (VET),
— rotational energy transfer (RET),
— collision-induced intersystem crossing (CIISC).
12.1 Basic radiative processes in a two-level system; Einstein coefficients
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Figure 12.1: Absorption, stimulated emission, and spontaneous emission.
2
= − 1
= 12 () 1 − 21 () 2 − 21 2 (12.1)