Flash photolysis and Shock tube method

In 1967 the Nobel prize in chemistry was awarded to Manfred Eigen, Ronald George Wreyford Norrish for their co-discovery of Flash photolysis in 1949.
Flash photolysis is used to extensively to study reactions that happen extremely quickly, even down to the femtosecond depending on the laser that is used. The technique was born out of cameras developed during and shorty after WWII, which were used to take pictures of fast moving planes, rockets and Missiles.
Since then the technology of laser and optics has progressed allowing faster and faster reactions to be studied.

1. Seminar presented on, “ Flash photolysis and Shock tube method ” Presented by Kotresh M Register No.: P11AZ22S104001 I M.Sc., I Semester. Under the Guidance Pruthvi raj. K Faculty DOS & R in Organic Chemistry Tumkur University, Tumakuru .

2. CONTENTS INTRODUCTION FLASH PHOTOLYSIS SHOCK TUBE METHOD APPLICATIONS CONCLUSION REFERENCE

3. INTRODUCTION In 1967 the Nobel prize in chemistry was awarded to Manfred Eigen, Ronald George Wreyford Norrish for their co-discovery of Flash photolysis in 1949. Flash photolysis is used to extensively to study reactions that happen extremely quickly, even down to the femtosecond depending on the laser that is used. The technique was born out of cameras developed during and shorty after WWII, which were used to take pictures of fast moving planes, rockets and Missiles. Since then the technology of laser and optics has progressed allowing faster and faster reactions to be studied.

4. Flash photolysis Flash photolysis and shock tube methods apply a large perturbation to a relative system and there by generating one or more respective intermediates . The reactions are followed by spectroscopic method. The reaction is initiated by an intense flash of visible or ultraviolet light generated by a photoflash lamp. The duration of the flash, about 5 to 15 microseconds is shorter than the reaction time scale. The intermediates generated can be probed in real time using spectroscopic methods. The absorption spectrum of the intermediate has to be determined at fixed intervals after the initial flash. The reaction cell(RC) is a quartz cylinder of length up to 1m. Both the ends of the cylinder are plane windows.

5. Schematic representation

6. The photoflash lamp tube is parallel to the reaction cell suitably placed reflectors increase the intensity of light falling on the sample. The photoflash has a capacitor connected to the two electrodes. In the experiment the reactants are put in a cylindrical quartz vessel which is present next to the photolytic flash tube is coated with Mgo reflector. Flash is obtained by the discharge of the high capacitor in a flash enclosing a gas at low pressure.

7. Monochromatic light from a lamp passed through the sample and wave length is selected by monochromator. Than intensity is measured by the photomultiplier and than display on oscilloscope.

8. APPLICATIONS Its applicable for the observation of excited singlet state, short lived excited triplet state and chemical event in the nanosecond. The method is valuable tool for the identification of transient chemical intermediate and hence for the study of mechanism of fast reaction.

9. SHOCK TUBE METHOD A Shock tube is an impulse reactor that generates shock wave to near-instantaneously heat a test gas. Construction & Working of Shock tube Construction The reaction system is taken in a stainless steal ,through which shock wave is passed. This shock tube consists of two sections one is a Driver section and another one is Driven section , far the end of the driver section is connected to the piston ,the driver and driver section is mounted by a pressure gauge and pressure sensors respectively. These are separated by a metal diaphragm , inside the driver section use driven gas(high pressure) and test gas in driven section(low pressure). Driver and driver section are called upstream end and downstream end.

10. Schematic representation

11. WORKING When the piston is moved towards driver section, the gas molecules are moves towards driven sections, the diaphragm is ruptured due to the force of the piston, gas molecules hit to diaphragm Then these gas molecules entered to driven section at a particular time diaphragm completely Due to the high pressure gas molecules hit to the end of the driven section of closed end. After hitting the gas molecules comes to downstream end and produce shockwave.

12. A PPLICATIONS Its applicable for the observation of excited singlet state, short lived excited triplet state and chemical event in the nanosecond. The method is valuable tool for the identification of transient chemical intermediate and hence for the study of mechanism of fast reaction Chemical shock tubes to study high temperature chemical kinetics The application of the shock wave research into bio-medical and industrial applications

13. CONCLUSION During photolysis reactions can be proceed in very short time like in nanoseconds. The shock tube is an instrument used to replicate and direct blast waves at a sensor or model in order to stimulate actual explosion and their effects ,usually on a smaller scale.

14. REFERENCE Principles of Physical chemistry by Puri Sharma Pathania E Pathshala

15. Thank you