The objective of the seminar

The objective of this seminar is to give a bird’s eye view on the topic of Femtochemistry.

Femtochemistry

The End of the Road

Definition

Femtochemistry is the area of physical chemistry that studies chemical reactions on extremely short time scales , approximately 10-15 seconds (one femtosecond , hence the name)

The date of birth : 1987

The Founder :

Professor Ahmed Hassan Zewail

Declaration and recognition :

Professor Zewail was awarded the 1999 Noble Prize in Chemistry for showing that it is possible with rapid laser technique to see how atoms in a

molecule move during a chemical reaction .

The Theory

The chemical reaction events at the microscopic level

1 -The actual atomic motions in a chemical reaction have never been observed (2000 yrs)

2 -During a chemical reaction : )i (bonds break )ii (bonds formed )iii (bonds geometrically change

These processes are ultrafast .

Why do we need a fs?

Calculation of the speed of atomic motion 1 km/s i.e. 1m/10-3 sAtomic distances about 0.1 nmi.e. it takes 100x10-15 s (100 fs ) [1fs =10 -15 s ; ] [1fs to 1s is as 1s to 32 millions yrs ]

The challenge is to “see” such an event!!!

To succeed we need : )1 (Time-resolution (fs) to freeze structures

before any vibration or rotation takes place)2 (Time reference – the Cs clock )3 (Atomic-scale resolution (0.1 nm ) )4 (Transition from kinetics to dynamics )5 (Heisenberg uncertainty principle

Race against time

)1 (Before a century time scale was (decade, yr , month , day , hr. , s )

)2 (In the last 100 yrs time resolution witnessed major strides ; 1923(10-3 s flow systems ),1950 (10-6 s flash photolysis –

ESR), 1960 (ns), 1966(ps) ,1974 )sub.ps,(1987 (fs)

The end of the ROAD

With femtosecond spectroscopy we have reached the end of the road.

NO CHEMICAL REACTIONS TAKE PLACE FASTER THAN THIS!

Experiment Femtochemistry exploits the pump – probe

technique : ) i (A pump laser pulse initiates the chemical reaction.

) ii (The probe laser pulse records a snapshot of the

chemical reaction .

why Lasers ? 1 -well – defined λ

2 -short pulse ) same λ , coherent phase , polarization .(

PROFESSOR : AHMED ZEWAILTHE KING OF FEMTOCHEMISTRY

* NATIONALITY : EGYPTIAN AND AMERICAN * BORN IN 1946 , DAMANHOUR ,EGYPT * B.S., U. OF ALEXANDRIA, EGYPT (1967)

* M.S., U. OF ALEXANDRIA, EGYPT (1969) * Ph.D. U. OF PENNSYLVANIA, U.S.A. (1974)

* PROFESSOR OF CHEMISTRY * PROFESSOR OF PHYSICS

* DIRECOR OF PHYSICAL BIOLOGY CENTER FOR ULTRAFAST SCIENCE & TECHNOLOGY AT

CALTECH * PRESIDENT OBAMA COUNCIL OF ADVISERS

ON SCIENE AND TECHNOLOGY * FIRST UNITED STATES SCIENCE ENVOY TO

THE MIDDLE EAST * AUTHOR OF 14 BOOKS AND 554 PUBLISHED

PAPAERS

Unifying disciplines

* Professor Zewail is now a professor of chemistry , a professor of physics and the

director of the institute of physical Biology .