The document discusses actinometry, a technique used to measure light intensity in photochemical applications, detailing its historical background, types of actinometers, and their instrumentation. It explains the concept of quantum yield and presents various actinometer types, such as chemical and physical actinometers, along with their procedures, advantages, and limitations. Additionally, the document highlights the applications of actinometry in fields like photochemical research, climate studies, and astronomy, while addressing challenges and future directions in the field.

1. Actinometry in
Photochemistry
Measuring Light Intensity for Photochemical
Applications
- By : Aniket Singh

2. Introduction to Actinometry
 Actinometry is the technique used to measure the
number of photons in a specific wavelength range.
 Used to determine the light intensity or photon
flux in photochemical experiments.
 Actinometry allows for accurate quantification of
light, ensuring reproducibility and efficiency of
reactions.
 The device or chemical system used to measure
the light intensity is called Actinometer.

3. HISTORY
The first actinometer was invented by
John Hershel in 1825 for the
investigation of solar radiation in
relation to meteorology research,
based on temperature changes
induced by absorption of light by a
copper sulfate solution.

4. An actinometer instrument from the 1800s designed by Jules
Violle and used to estimate the temperature of the Sun's
surface.

5. QUANTUM YIELD AND ITS
IMPORTANCE
• The efficiency of a photochemical process is expressed
in terms of Quantum Yield (Φ) which is defined as
number of molecules reacting per quantum of light
absorbed.
• Critical for determining the efficiency of
photochemical process.
Φ =
Number of molecules reacting in a given time
Number of quantum of radiation absorbed in
same time

6. Types of Actinometers
• Chemical Actinometers: Chemical actinometers are devices used
to measure the intensity of light based on photochemical
reactions.
1. Ferrioxalate Actinometer: Fe(II) formation from Fe(III) under
UV light.
2. Reinecke's Salt Actinometer: Involves photoreduction of
Reinecke's Salt.
3. Uranyl oxalate Actinometer
• Physical Actinometers: Physical actinometers measure light
intensity through the detection of physical changes such as
changes in electrical properties, temperature, or radiant power.
- Photodiodes: Convert light into an electrical current.
- Thermopiles: Measure temperature change caused by light
absorption.
- Photocell: Converts light energy into electrical energy

7. Instrumentation of Actinometer
 Light Source: Depending on the application, this could be a UV
lamp, a visible light source, or a combination of light sources.
 Sample holder: Often a quartz cuvette or glass vessel that holds
the chemical solution or device that undergo physical change.
The material of the holder should be transparent to the light being
measured.
 Chemical solution or measurement device: Detects and
quantifies the chemical or physical changes in response to light.
 Detector: Measures the physical or chemical changes in the
sample.
 Measurement and Data Acquisition System: Records and
analyzes the data obtained from the detector.
 Calibration Standards: Provides known references for
calibrating the actinometer and ensuring accurate measurements.

8. FERRIOXALATE ACTINOMETER
 Reaction:
[Fe3+
(C2O4)3 ]3-
hυ →[Fe2+
(C2O4)2]2-
+ C2O4
-
[Fe3+
(C2O4)3]3-
+ C2O4
-
→ [Fe3+
(C2O4)3]2-
+ (C2O4)2-
[Fe3+
(C2O4)3]2-
→ [Fe2+
(C2O4)3]2-
+ 2CO2
 Procedure:
1. Prepare a standard ferrioxalate solution.
2. Expose to light for a fixed time.
3. Measure concentration of Fe(II) using spectrophotometry.
4. Calculate photon flux using known quantum yield.
 Advantages: Broad wavelength sensitivity, high quantum yield
accuracy.
 Limitations: Sensitive to impurities and temperature variations.

9. Uranyl Oxalate Actinometer
Reaction:
Procedure:
 Dissolve uranyl oxalate in an appropriate solvent.
 Place the solution in a radiation chamber and expose it to
the radiation source.
 After exposure, use spectroscopic methods to analyze the
concentration of uranyl ions and/or oxalate ions.
 Use the measured changes in concentration to calculate the
dose of radiation using calibration data.
UO2
2+
+ hv → (UO2
2+
)*
(UO2
2+
)* +
oxalate→ UO2
2+
+ CO2 + CO + H2O

10. PHOTOCELL
 A device that detects light and converts
light energy directly into electrical energy.
 A photocell consists of a photosensitive
cathode and a collector anode enclosed in an
evacuated bulb.
 Light quanta of energy greater than the
threshold energy of metal causes ejection of
electrons which are collected by anode and
current flows in a circuit.
 The intensity of current generated will be
linearly proportional to the incident light
intensity.

11. THERMOPILES
 An electronic device that converts
thermal energy into electrical
energy.
 It is composed of several
thermocouples connected usually
in series , or less commonly, in
parallel.
 Thermophiles are thermocouples
connected in series and generate
E.M.F on heating.

12. Applications of Actinometry
 Photochemical Research: Quantify light source for
accurate reaction rates.
 Climate Studies: Monitoring solar radiation to
understand global warming trends.
 Weather forecasting: Measure solar and UV radiation
to improve weather models and forecasts.
 Solar Observation: Measure solar radiation to study
solar activity and its effects on Earth.
 Astronomical Research: Calibrate telescopes and
instruments by measuring light intensity from celestial
objects.

13. Challenges and Future Directions
• Challenges: Sensitivity to experimental
conditions, need precise calibration.
• Future Developments: Advancements in
sensor technology and new chemical
actinometers.
• Conclusion: Importance of actinometry in
advancing photochemical research and
applications.

14. THANK YOU