1. Experimental techniques in reaction kinetics
Kísérleti módszerek
Experimental techniques in reaction kinetics

2. Techniques classified
Batch reactors vs. flow reactors
Online methods: real-time in situ detection
Offline methods: — aliquot from the batch — “quenched flow”
Pseudo-first order (isolation or flooding) method (only if relative concentrations are available)
− 𝑑 𝑐 1 𝑑𝑡 =𝑘 𝑐 1 𝑐 2
− 𝑑 𝑐 1 𝑑𝑡 =𝑘′ 𝑐 1
𝑘′=𝑘 𝑐 2
1. measurement of both 𝑐 1 and 𝑐 2
1. 𝑐 1 << 𝑐 2 ; series of measurements at several 𝑐 2 (time dependence of 𝑐 1 )
2. 𝑘 from the above data
2. 𝑐 2 dependent 𝑘′ from each series
3. 𝑘 from the above 𝑘′( 𝑐 2 ) data
Unbiased; higher precision
Biased; lower precision

3. “classical” techniques (time-limit: manipulation time; ~ 1 s)
C4H9Cl + H2O → → C4H9OH + H+ + Cl–
Thermometer
Electrode
Inlet for C4H9Cl
Conductivity meter
Reaction mixture
PC or chart recorder
Voltage
Thermostatted jacket
Magnetic stirrer
Time

4. Discharge flow (time-limit: mixing time; ~ 1 ms)
(„gyorsáramlásos módszer”)
H + NO2 → OH + NO
To diffusion pump
Flow controller
OH + C6H12 → products
Photomultiplier
Microwave discharge
To rotary pump
Movable injector
Monitoring cell
Flow tube (reactor)
Frequency doubling crystal
Excimer laser
Sample/hold device
Dye laser
Trigger pulse

5. Resonance fluorescence detection
(RF)
Photo-multiplier tube
Microwave discharge cavity
Hydrogen Lamp
H2 / He mix inlet
outlet
Processes in the detection cell
Processes in Resonance Lamp
a) MW radiation dissociates some H2
a) H atoms absorb photons and become electronically excited
b) H atoms absorb energy and become electronically excited
b) A portion of isotropically emitted fluorescence photons is detected
c) H atoms relax, emit charac-teristic radiation directed into the cell

6. Laser induced fluorescence detection
(LIF)
Energy
v’ = 2
v’ = 0
Excitation pulse (282 nm)
Fluorescence (308 nm)
etc.
v’ = 1
Excitation laser tuned to one particular rotational level
v’’ = 2
v’’ = 0

7. Quadrupole mass selector
Mass spectrometry
He buffer gas
Quadrupole mass selector
Ion detector
To pumps
C2H5+ detected
Movable injector
Flow tube (reactor)
Ion source
To pumps
To pumps
Microwave discharge
Cl + C2H6 → HCl + C2H5
Cl2 / He
C2H5 + O2 → C2H6O2 → C2H4 + HO2

8. Continuous liquid flow tube
(„folyamatos áramlásos reaktor”)
Reactant A
Source
Mixing chamber
Motor driven syringe plungers
Flow tube
Reactant B
Moveable detector system (spectrometer)
Detector

9. Stopped flow system („megállított áramlásos reaktor”)
Computer control and data acquisition
Limit switch
Effluent
Reactant A
Mixing chamber
Motor driven syringe plungers
Reactor
Spectrometer
Reactant B

10. High pressure inert driver gas
Shock tube
Real time detection
Reaction mixture
High pressure inert driver gas
Diaphragm
Before diaphragm breaks
Pressure
After diaphragm has broken
Incident shock
Pressure

11. Flash photolysis (time-limit: flash pulse width; ~ 1 μs)
Nobel Prize: Norrish, Porter; 1967
Photolysis flash
Spectrograph
Reactor tube
Detection flash

12. Laser photolysis (time-limit: laser pulse width; ~ 1 μs down to 1 fs)
Beam dump
To exhaust
Valve to control pressure in reaction vessel
Heatable stainless steel reaction vessel
Xenon arc lamp
Monochromator
PMT
Slow premixed gas flow
Flow controller
Digitizer (A/D)
Flow controller
Gas inlets
Computer control and data acquisition
Flow controller

13. Increase in time resolution
időfelbontás
Increase in time resolution
1011 times increase within 36 years!!
amplified lasers + pulse compression
time, seconds
picosecond lasers (ring lasers)
nanosecond lasers (mode locking)
flash photolysis + relaxation
flow methods
year

14. Principles of laser operation (”lasing”)
Light Amplification by Stimulated Emission of Radiation
Pumping energy
Tuning device
Gain medium
Auxiliary parts
High reflector (non-transparent)
Output coupler (partially transparent)

15. Pulsed lasers Pumping energy Tuning device Saturable absorber
Gain medium
High reflector (non-transparent)
Output coupler (partially transparent)

16. Colliding Pulse Mode-locked lasers
(CPM lasers)
Tuning device
Amplifier
Output coupler
Absorber
Pumping laser

17. Time scale Time window of elementary reactions human lifespan
időskála 2
Time scale
Time window of elementary reactions
molecule - photon interaction
nuclear motion in atomic nuclei
atomic nucleus - neutrino interaction
lifetime of the triplet excited state
lifetime of the singlet excited state
molecular rotation
molecular vibration
electron- and energy- transfer
solvation
vibrational relaxation
human lifespan
length of a day
one minut
appearance of humans
the age of Earth
1015
1012
109
10 -15
10 -18
10 -21
10 -24
106
103
10 -6
10 -3
10 -9
10 -12 1
tera-
giga-
mega-
kilo-
micro-
milli-
nano-
pico-
femto-
atto-
zepto-
yocto-
peta-
CPU clock cycle time
second

18. pump-probe
Spectroscopy with femtosecond time resolution: experimental arrangement
amplifier
sample
detector
H2O
delay
excitation
probe
reference
Nd:YAG laser
Ar- ion laser
CPM laser
(1 fs = 0.3 m path length)
Laser technics:

19. ultrashort pulse  coherence and selectivity
pump-probe 5
Principles of the femtosecond experiment
ultrashort pulse  coherence and selectivity
1 fs = 0.3 m path length
potential energy
excitation (Ig)
measurement (Im)
reaction coordinate
time
Pulse width: 10…100 fs

20. Experimental results ICN → I···CN → I + CN LIF signal potential energy
pump-probe 6
Experimental results
ICN → I···CN → I + CN
LIF signal
potential energy
reaction coordinate
delay time, fs

21. Reaction dynamics Molecular beam Moveable detector
Collimators and velocity selectors
Heated oven
Effusive beam
Reaction chamber 10–7 torr
Molecular flow (collision free)
Second stage pumping
Continuum flow (collisional relaxation)
First stage pumping
High pressure source (> 300 torr)

22. Angular dependence Scattering angle in a centre of mass system
Density map: HCl intensity

23. Angular and energy dependence
F + D2  DF(v) + D
v = 1
v = 2
Constant total energy
v = 3 0°
180°
v = 4
Contour lines: equal velocity of DF

24. State selective optical detection
CX molecules
B atoms from microwave discharge
Microwave discharge generated
A atoms
Sapphire window
Liquid N2 cooled reaction vessel (cryopump)
Split mirror optics (White cell) to collect and focus emission onto detector
To pumps