1. 9. Reaction dynamics /

2. Effect of isotope masses on reaction rates Áhrif samsætumassa á hraða efnahvarfa
path
path

3. path
path

4. path
path
Effective activation energy

5. path
path
Effective activation energy

6. Photochemistry can be dramatically
different from “ordinary” chemistry
See example below

7. photochemistry example:
Ljósefnafræði ; Dæmi /
photochemistry example: Cl Ar

8. photochemistry example:
Ljósefnafræði ; Dæmi /
photochemistry example: . Cl . Ar .

9. photochemistry example:
Ljósefnafræði ; Dæmi /
photochemistry example: Ar Cl

10. photochemistry example:
Ljósefnafræði ; Dæmi /
photochemistry example: + - Cl Ar Cl

11. photochemistry example:
Ljósefnafræði ; Dæmi /
photochemistry example: Ar Cl Cl

12. „Photographing“ reactions; Nobel price in Chemistry, 1999
* Sjá:

13. Reaction rate and mechanism:
A + B C D
Hr.efnahv.

14. „Photographing“ reactions; Nobel price in Chemistry, 1999
Reaction rate and mechanism:
A + B C D
Rate = k[A] [B]; k = Aexp(-Ea/RT); k <= [A] vs t measurements
Arrhenius: Nobel price 1903
Hr.efnahv.
Hr.efnahv.

15. Theory concerning transition state ::
Theory concerning transition state :
Henry Eyring
Michael Polanyi #
A..B 1 2
A B
C D
# short lived transition state:
Lifetime » time of a vibration, typically – sec. 1: 2:
Kenning

16. Experiments by use of molecular beams ::
Experiments by use of molecular beams :
Molecular
beam
collision
Reagents and
products
detected
Moveable detector
-Transition state properties determined from scattering measurements
John C. Polanyi
Nobel price, 1986: Dudley Herzbach
Yuan Lee
Bunur

17. “Photographing reactions”
1985 -
“Photographing reactions”
i.e. Absorption measurements for transition state species vs. time (t) for
Dt £ s:
Absorption
measurements by
light pulses
10-15 s AB CD
A . .B
C ..D
A B
0, s
C D
“Femtosecond spectroscopy”
Nobel price in chemistry 1999:
Prof. Ahmed Zewail, Caltech.
Ljosm.

18. Verðl.

19.
Femtol.

20. All stages of the reaction simultaneously, i.e.
How / What?
A + B C D
All stages of the reaction simultaneously, i.e.
Too much!
Hvernig?

21. Coordination i needed :
Example: “½ reaction”, e.g.: ICN# I + CN, i.e.: I
CN#

22. Coordination i needed :
Example: “½ reaction”, e.g.: ICN# I + CN, i.e.: I CN
ICN#
ICN
I + CN
Formed by absorption of
a femtosec. laser puls
Absorption measurements
½ hvarf

23. Procedure:
ICN-Tilr.

24. In detail: ICN# I + CN Absorption measurements: ICN Results:
ICN-niðurst.

25. (a)
(b)
[NaI# Na..I# ] Na I
NaI
(a)
NaI#
(b) Na
NaI

26. Energy
Stilbene(1)

27. Stilbene(2)

28. IH..OCO [I..H..O..CO] I +HO+CO Van der Jet Waals expansion/ Molecular
“Molecules”
Jet
expansion/
cooling
Molecular
beam
IH+OCO

29. C4H C4H8# C2H4 + C2H4
???
Cyclob.

30. Dissociation of C2F4I2 : . ?(1) . . . ?(2) . . C2F4I2 C2F4 + 2I: I F I
C C
C C F . F F I F I . I F F I F I F F . F
?(2)
C C
C C
C C . F . F F I F I F F I
C2F4I2

31. mynataka

33. Energy

34. 5

35. 6

36. 7

40. 8

42. 9

46. 10

53. A + M ???
M1 + M ???
A + B C + D
Reaction cross section:

54. A + M ???
M1 + M ???
A + B C + D
Reaction cross section:
Cross section = s = <d>2p d
But ions:

55. But ions:
Reaction cross section:
A+ + B C + D +
F µ 1/r2 - + +

56. But Ions:
Reaction cross section:
A+ + B C + D + - + +

57. + + But ions: Reaction cross section: A+ + B C + D
Collision frequency much larger +

58. + A + M ??? M1 + M2 ??? A + B C + D Reaction cross section: Ions:
Collision cross
section =
s >> <d>2p d