Actinometry-sobia.pptx

IMPORTANT

1. Actinometry

2. Presentation Outline Quantum Yield Actinometer History Physical Detectors (Physical Actinometer) Chemical Actinometer 2 Example (Uranyl oxalate Actinometer)

3. The quantum yield (ϕ) is defined as the number of moles of product formed per Einstein ( Numbers of quanta) of light absorbed by the photosensitive agent . Its value can be unity, less than unity or may be greater than it. Quantum yield

4. Counting photon is inefficient, there is a tendency to miss a lot of photons during counting .

5. An actinometer is a chemical system or physical device which determines the number of photons in a beam of light or absorbed per unit time . This phenomenon is known as Actinometery. Actinometer

6. History The first actinometer was invented by  John Herschel 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. 

7. It works based on the principle that “the rate of photolytic conversion of molecules within an actinometer cell is equal to the rate of absorption of photons in the actinometer” . Principle of Actinometer

8. Actinometer are of two type. It can be a Physical Detectors Chemical Actinometer (Chemical Actinometer is also known as dosimeter.) Types of Actinometer

9. Physical detector may be a Thermophile Photocell Photomultiplier Physical Detector

10. It is 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. Thermopile

11. Working of Thermopile

12. Thermopile

13. A device that detects light and converts light energy directly into electrical energy.   A photocell consist of a Photosensitive cathode and collector anode enclosed in an evacuated bulb . Light quanta of energy greater than the threshold value of metal cause ejection of electron which are collected by anode and current flow in circuit. The intensity of current generated will be linearly proportional to the incident light intensity. Photocell

14. Photocell

15. Although these instruments, based on photo physics, are Accurate user-friendly mostly cheap But still their direct application in photochemistry is very limited compared with chemical actinometer. Limited use of Physical detectors

16. Chemical Actinometery involves measuring the radiation intensity through the yield of the chemical reaction. There are several types of chemical actinometer such as Uranyl Oxalate Actinometer Ferrioxalate actinometer Reinecke’s salt Actinometer Chemical Actinometer

17. Uranyl oxalate actinometer consist of liquid solution of oxalic acid  containing uranyl sulfate. Light in the wavelength range of ultraviolet region   decomposes  the oxalic acid. Decomposition occur (through a complex region involve initial absorption of light energy by uranyl ion) into mixture of Carbon dioxide, carbon monoxide and water molecules. Uranyl oxalate Actinometer

18.  A standard solution is generally irradiated with light of the proper wavelength and of known intensity, and the quantity of oxalic acid decomposed is accurately measured by titration with potassium permanganate . The quantity of oxalic acid decomposed and the quantity of light energy absorbed can then be used as a scale from which to predict either quantity when the other is known or measured. UO 2 +2 + hv ( UO 2 +2 ) ( UO 2 +2 ) + C 2 H 2 O 4 UO 2 +2 + H 2 O + CO 2 + CO

19. Thank you 19