levine, pp. 800-804 photochemistrycourse.sdu.edu.cn/download2/20191014214820585.pdflaser cooling...

§10. 6 Photochemistry

Out-class reading:

Levine, pp. 800-804 photochemistry

Energy efficiency:Photosynthesis:

6CO2 + 6H2O + nh C6H12O6 + 6O2

rGm = 2870 kJ mol-1

For formation of a glucose, 48 light quanta

was needed.

%7.354.16748

2870

6.5 Quantum yield and energy efficiency


Photosensitive reaction

Reaction initiated by photosensitizer.

6CO2 + 6H2O + nh C6H12O6 + 6O2

When reactants themselves do not

absorb light energy, photoensitizer can

be used to initiate the reaction by

conversion of the light energy to the

reactants.

Chlorophyll A, B, C, and D

Porphyrin complex with magnesium

6.6 The way to harness solar energy—photosynthesis


Light reaction: the energy content of the light quanta is converted into chemical energy.

Dark reaction: the chemical energy was used to form glucose.

Fd is a protein with low molecular weight

4Fd3+ + 3ADP3- + 3P2-

4Fd2+ + 3ATP4- + O2 + H2O + H+

3ATP3-+ 4Fd2++ CO2+ H2O + H+ 3P2-

(CH2O) + 3ADP3- + 3P2- + 4Fd3+

8h

6.6 The way to harness solar energy


All the energy on the global surface comes from the sun.

The total solar energy reached the global surface is 3 1024 Jy-1, is 10,000 times

larger than that consumed by human being.


Only 1~2% of the total incident energy

is recovered for a field of corn.


Solar heating:



Solar electricity: photovoltaic cell Solar chemical energy

photoelectrochemical cell

Photolysis of water



Solar electricity: photovoltaic cell

Solar chemical energy

photoelectrochemical cell

Photolysis of water/

Photooxidation of pollutant

Photochemical reaction—photocatalysts ??

S + h S*

S* + R S+ + R-

4S+ + 2H2O 4S + 4H+ + O2

2R-+ 2H2O 2R + 2OH-+ H2

S = Ru(bpy)32+



Photolysis of water based on semiconductors


TiO2 the most important photocatalyst.

Modification of TiO2.


6.7 The way to produce light:

Photoluminescence, Electroluminescence, Chemiluminescence,

Electrochemiluminescence, Light-emitting diode

Chemiluminescence


The reverse process of photochemistry

A + BC AB* + C

High pressure:

collision deactivation

Low pressure:

radiation transition

CF3I CF3 + I*

H + Cl2 HCl* + Cl

A+ + A- A2*

Emission of light from excited-state dye.

firefly

The firefly, belonging to the family of

lampyridae, is one of a number of

bioluminescent insects capable of

producing a chemically created, cold light.



MEH-PPV

S.-Y. ZHANG, et al. Functional Materials, 1999, 30(3):239-241

Emission of light from excited-state dye molecules can be driven by the electron

transfer between electrochemically generated anion and cation radicals:

electrochemiluminescence (ECL).



6.8 Laser and laser chemistry:

1917, Einstein proposed the possibility of laser.

1954, laser is realized.

1960, laser is commercialized.

Population inversion

light amplification by stimulated

emission of radiation



(1) Chemical HF - HBr laser: 2.7 m

and 4.2 m

(2) A chemical non-chain DF laser 3.5

to 4.1 m

(3) Supersonic chemical oxygen-iodine

lasers

(4) Chemical HF laser

(5) N2O-laser

(6) Pulsed HF/DF lasers


(1) High power: emission interval: 10-9, 10-11, 10-15.

100 J sent out in 10-11s =1013 W；

temperature increase 100,000,000,000 oCs-1

(2) Small spreading angle: 0.1 o

(3) High intensity: 109 times that of the sun.

(4) High monochromatic: Ke light: = 0.047 nm,

for laser: = 10-8 nm,

Specialities of laser




Laser-induced reaction

Laser Heating--absorption

Laser cooling—emission

Regulation of

molecular state

Laser cooling refers to a technique in which

atomic and molecular samples are cooled down

to near absolute zero through the interaction

with one or more laser fields.

All laser cooling techniques rely on the fact

that when an object (usually an atom) absorbs

and re-emits a photon, its momentum changes.


William Daniel Phillips

born Nov. 5, 1948

American physicist.

For Laser cooling

朱棣文(born Feb. 28, 1948)

American physicist

cooling and trapping of

atoms with laser light

Claude Cohen-Tannoudji

born 1 Apr. 1933

a French physicist.

He shared the 1997 Nobel Prize

in Physics.



Discussion

(1) Should photochemical processes obey thermodynamics?

(2) Can laser cooling break the second thermodynamic law?

(3) How can we increase the energy efficiency of TiO2 in photolysis of

water?

(4) Explain the principle by using electrooxidation and reduction to

produce light based on polymeric semiconductor.


levine, pp. 800-804 photochemistrycourse.sdu.edu.cn/download2/20191014214820585.pdflaser cooling...

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