cso 202a atoms molecules and photons - iit kanpurhome.iitk.ac.in/~madhavr/cso202a.pdf · cso 202a...
Post on 25-Aug-2018
281 Views
Preview:
TRANSCRIPT
CSO 202A
Atoms Molecules and Photons
Instructors: Dr. Manabendra Chandra and Dr. Madhav Ranganathan
Lec: M,W,Th: 12:00-12:50 L3
Piazza sign-up link: piazza.com/iitk.ac.in/secondsemester2017/cso202Piazza class link: piazza.com/iitk.ac.in/secondsemester2017/cso202/home
Tutors: Sourav Karmakar (souravk@iitk.ac.in) Navin Subba (navins@iitk.ac.in) Aqeel Malani (aqeel@iitk.ac.in)
Tut: Friday: 17:00-17:50 T207-209
CSO 202A : Atoms Molecules and Photons
Grading scheme:
Quiz-1 (45 mins): 15% (module 1) 3rd Feb. 2017Quiz-2 (45 mins): 15% (module 3) 31 st Mar. 2017
MidSem (2 hrs): 35% (module 1 + module 2) EndSem (2 hrs) : 35% (module 3 + module 4)
CSO 202A : Atoms Molecules and Photons
2007: Gerhard Ertl "for his studies of chemical processes on solid surfaces"2013: Martin Karplus, Michael Levitt and Arieh Warshel "for the development of multiscale models for complex chemical systems".2014: Eric Betzig, Stefan W. Hell and William E. Moerner "for the development of super-resolved fluorescence microscopy".
Path-breaking research works in the field of chemical reaction dynamics
Module 2 Module 1
Module 3Module 4
CSO 202A
CSO 202A : Atoms Molecules and Photons
Course plan
Module 1: Chemical Reaction Dynamics with Molecular BeamsModule 2: Ultrafast Chemical Reaction Dynamics with Ultrashort- Pulsed LasersModule 3: Catalytic Reactions on Solid SurfacesModule 4: Chemistry with Supercomputers
CSO 202A : Atoms Molecules and Photons
This way of writing down chemical reactions, using arrows and symbols, is ‘incomplete’
Consider the reaction:
Do rates depend on internal quantum states of the reactants? What are the internal quantum states of the products? What is the dependence of chemical reactivity on molecular
orientation? Dependence on the impact of collision? What are the nature of reaction intermediates and their
subsequent decay dynamics in case of complex polyatomic molecular reactants?
CSO 202A : Atoms Molecules and Photons
Answers can be found by doing experiments using crossed molecular beam technique
2Na + O2 → Na2O + O
CSO 202A : Atoms Molecules and Photons
Dudley R. Herschbach
Yuan T Lee John C Polanyi
The Nobel Prize in Chemistry 1986
"for their contributions concerning the dynamics of chemical elementary processes"
CSO 202A : Atoms Molecules and Photons
Module 2 :
Ultrafast Chemical Reaction Dynamics with Ultrashort- Pulsed Lasers
CSO 202A : Atoms Molecules and Photons
Consider a chemical transformation
CH3I + Na → CH3---I----Na → CH3 + NaI
Transition state
In any chemical reaction the motions of the electrons and nuclei of atoms determine how the molecules interact, and those interactions in turn create the forces that govern the reaction's dynamics.
If one can determine how molecular motions change during the critical transition phase, we can understand how new chemical bonds form and old ones disappear.
CSO 202A : Atoms Molecules and Photons
QuestionHow can one study transition state(s) in real time?
Answer
Need ultrafast probe and detection technique
CSO 202A : Atoms Molecules and Photons
Consider a simple dissociation reaction
ICN → I + CN
J. Chem. Phys., 1987, 87(4), 2395
CSO 202A : Atoms Molecules and Photons
Ahmed Zewail
The Nobel Prize in Chemistry 1999
“for his studies of the transition states of chemical reactions using femtosecond spectroscopy"
CSO 202A : Atoms Molecules and Photons
Molecular structures for a reaction in progress involving two molecules (bimolecular). The diatomic iodine molecule (I2, top) is split by exchange of an electron with the ring molecule benzene (C6H6).
CSO 202A : Atoms Molecules and Photons
Molecular structures for a reaction in progress involving two molecules (bimolecular).
CSO 202A : Atoms Molecules and Photons
Fritz-Haber synthesis of Ammoia
Consider the reactionN2 + 3 H2 ====> 2NH3
● Simple looking reaction, Exothermic reaction
● Requires 700 K, 200 Bar pressure
● Negligible rate without a catalyst – Fe
● Fritz Haber: Nobel Prize 1918 (Discovery)
● Carl Bosch : Nobel Prize 1931 (Commercialized the Haber process)● Elucidation of the mechanism : Gerhard Ertl: Nobel Prize 2007
Why is it such a big deal ?
CSO 202A : Atoms Molecules and Photons
Greatest discovery of the last century ??● Ammonia production is the first stage of fertilizer preparation and the most difficult
Fritz-Haber process replicated that
of N-fixing bacteria and transformed the N-cycle Nitrogen compounds are also used in explosives – World War II
CSO 202A : Atoms Molecules and Photons
Nitrogen cycle
Chile Saltpeter NaNO3 : Natural source of Nitrates
CSO 202A : Atoms Molecules and Photons
Gerhard Ertl's Mechanism
The Physical Chemistry elements involved - Gas laws andtransport processes, reaction thermodynamics, kinetics, catalysis, surface chemistry, experiments, Ultra-High vaccuum
CSO 202A : Atoms Molecules and Photons
Why is this reaction so difficult ?N2 + 3 H2 ====> 2NH3
● N – N triple bond● One of the strongest known bonds● The inertness of N2 is well known● Liquid Nitrogen is frequently used to cool● Nitrogen is easily available in the atmosphere but fixing it artificially is very hard● Fe surface provides an easier way to break N-N bond N2 (g) ===> N2 (ads) ====> 2 N (ads)
CSO 202A : Atoms Molecules and Photons
● Consider the H2 molecule containing 2 electrons and 2 protons● How does one calculate the equlibrium bond length of H2 ?● Use the Born-Oppenheimer Approximation and fix protons andwrite Schrodinger equation
● Solve for lowest energy state and obtain E0(R)● Vary R and find Req corresponding to minimum E0
Module 4: Chemistry with Supercomputers
CSO 202A : Atoms Molecules and Photons
Chemistry with Supercomputers
But the above equation cannot be solved exactly !!!
● Numerical methods implemented on a computer● Req = 74.1 pm Bond dissociation energy = 4.52 eV
For large molecules, several bond lengths, bond angles have to be optimized !!!
● Need for advanced mathematical and numerical techniques
CSO 202A : Atoms Molecules and Photons
Nobel Prize in Chemistry 1998
Walter Kohn John A Pople
The Nobel Prize in Chemistry 1998 was divided equally between Walter Kohn "for his development of the density-functional theory" and John A. Pople "for his development of computational methods in quantum chemistry"
CSO 202A : Atoms Molecules and Photons
OK – That’s the structure of a single molecule, but what about dynamics ? What about behavior of a large number of molecules ?
One popular method is Molecular Dynamics Simulations using effective potential energies and classical dynamics
B. Alder and C. Wainwright (1955) and Aneesur Rahman (1959)
top related