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Photochemistry can be dramatically different from “ordinary” chemistry See example belowPowerPoint Presentation

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

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

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

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Nóbelsverðlaunin í efnafræði, 1999

* Sjá: http://www.hi.is/~agust/

* Sjá: http://www.hi.is/~agust/

Hr.efnahv.

Arrheníus: Nóbelsverðlaun 1903

Ljósmyndun efnahvarfa; Nóbelsverðlaunin í efnafræði, 1999

Gangur og hraði efnahvarfa:

A + BC + D

Hraði = k[A][B]; k = Aexp(-Ea/RT); k <= [A] vs t mælingar

Hr.efnahv.

Kenning um skammlíft milliástand:

KenningHenry Eyring

Michael Polanyi

#

A..B

1

2

A + B

C + D

# Skammlíft milliástand:

Líftími »tími tengjasveiflu, dæmigert 10-13 – 10-12 sek

1:

2:

Nóbelsverðlaun, 1986: Dudley Herzbach

Yuan Lee

1975-1990:

Tilraunir með sameindabunur:

BunurSameinda-

buna

Árekstur

Skynjun

myndefna/

hvarfefna

Hreyfanlegur

skynjari

-Ráðið í eiginleika milliástanda út frá dreifingu / endurkasti sameinda

“Femtósekúndu litrófsgreining”

Nóbelsverðlaunin í efnafræði 1999:

Próf. Ahmed Zewail, Caltech.

1985 -

“Ljósmyndun efnahvarfa”

Ljosm.Þ.e. Gleypnimælingar milliástanda vs tími fyrir tíma(bil) £10-12 s:

Gleypnimælingar

með ljósleiftrum

10-15 s

AB

CD

A . .B

C ..D

A + B

0,000000000000001 s

C + D

/flókið

Hvernig / Hvað?

Hvernig?A + BC + D

Öll stig hvarfsins koma fyrir samtímis, þ.e.:

Dæmi: “½ hvarf”, sbr.: ICN# I + CN, Þ.e.:

Gleypnimælingar

ICN#

I +CN

ICN#

Myndað með femtó-

sekúndu LASER-púls

gleypni

ICN

Skapa þarf “samhæfðar aðstæður”:

½ hvarfI

CN

ICN-Tilr.

C2F4I2

C2F4I2C2F4 + 2I:

.

I

F

I

F

F

?(1)

F

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

+

Collision cross

section =

s >> <d>2p

Reactioncrosssection:

A + M ???

M1 + M2 ???

A + B C + D

d