1. PHOTONS IN CHEMISTRY OUT WHY BOTHER?

2. E = h ν

4. λν = c [3 10 8 m/s]

5. ~ 450-750 nm Take 500 nm

6. Boltzman T [ o K]n 2 /n 1 3003 x 10 -42 4007 x 10 -32 10003.4 x 10 -13 2,0006 x 10 -7 5,0003 x 10 -3 6,4001 % 10,0005.7 % 20,00024 % 50,00056 %

7. Grotthuss-Draper law: Only the light absorbed in a molecule can produce photochemical Change in the molecule (1871 and 1841) Stark - Einstein: If a species absorbs radiation, then one particle is excited for each quantum of radiation absorbed

8. Stark - Einstein: If a species absorbs radiation, then one particle is excited for each quantum of radiation absorbed QUANTUM YIELD: Φ = The number of molecules of reactant consumed for each quantum of radiation absorbed Primary Φ ≤ 1 Sum of all primary Φ’s = 1

10. Photochemical kinetics

12. Transmittance Absorbance Beer’s Law

13. Molar extinction Coefficient ~250 L.mol -1 cm -1 Cross section ~10 -18 cm 2

14. NB 1: Beer fails when photochemistry happens NB 2: The photophysics Is hidden in σ (So we haven’t done much yet)

16. Absorption of a mixture

17. Photochemical kinetics STEADY STATE HYPOTESIS

18. NB 2: The photophysics Is hidden in σ (So we haven’t done much yet)

19. EINSTEIN COEFFICIENT # of transitions / second: Amplitude of TRANSITION MOMENT # of molecules degeneracy Radiation density =# of photons/unit freq.

20. Stimulated emission Spontaneous emission

21. Stimulated emission Spontaneous emission

24. Boltzman Planck

25. Oscillator strength

26. Lifetimes Einstein coefficients are rate constants

28. Heisenberg may have been here

29. Contributions to excited state lifetime  Natural lifetime  Pressure broadening  Saturaiton broadening  Doppler broadening NB: f(v) in a gas is Gaussian  Doppler line shape is Gausian

30. (depends on coordinates of electrons and nuclei And on time) electrons Nuclei

31. NB: Resonant frequency NB 1: I = f  e 0 and µ becomes permanent dipole NB 2: ν if as beat frequency NB 3:compare to nuclear vibrations

32. Compare 10 15 s -1 to IR: Nuclear motion is 2 orders of Magnitude slower than Electronic motion Born-Oppenheimer approximation

33. Orthogonal (no overlap) tells if allowed or forbidden: must be symmetric  selection rules Franck-condon factors

34. M x is odd:

35. One more parameter………. SPIN αβ updown ↑↓ +½-½

36. If we can separate space and spin (no spin-orbit coupling):

44. Conical Intersections R1 R2 E