L8_atm_femto_115b08

L8_atm_femto_115b08 - L8: Interaction of molecules with...

Info iconThis preview shows pages 1–12. Sign up to view the full content.

View Full Document Right Arrow Icon
L8: Interaction of molecules with light (Chapter 20) - General aspects of spectroscopy - Photochemistry - Stratospheric chemistry: the ozone hole - Tropospheric chemistry: smog - Global Warming Read:1. http://www.atm.ch.cam.ac.uk/tour/part3.html 2. Chapter 20, Sections 1 and 5 and lecture notes
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Detection of Intermediates And products Light emission Light absorption Excitation and detection achieved by laser irradiation
Background image of page 2
Femtochemistry How to measure reaction kinetics of fast reactions Femtosecond = 10 -15 s Picsosecond = 10 -12 s Nobel Prize 1999: Prof. Ahmed Zewail, Caltech
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Slow Reactions Protein folding, polymer formation Fast reactions: electron transfer, bond breaking, etc. Need a clever way to measure very short times.
Background image of page 4
Photodissociation R H-H E Bond energy Photon energy R eq H + H ( σ ) 2 ( σ ) 1 ( σ *) 1
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Quantitative description of adsorption: Beer-Lambert Law Probability that light is absorbed by a molecule in the cell: - concentration C - length of the cell The absorbance, A, is defined as: where I s - light transmitted through the filled cell I R - light transmitted through the reference cell R s I I A ln = I s I R
Background image of page 6
Beer-Lambert Law cl I I A R s ε = = ln where ε - molar extinction coefficient c - concentration l - cell length cl I I A g R s g = = log 303 . 2 10 ln n n g = = Notice: There may be some confusion about these definitions in the Solution Guide
Background image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Energy
Background image of page 8
Energy of light λ ν hc h E = = h=6.626x10 -3 Js - Plank constant c=3x10 8 m/s - speed of light λ (m) - wavelength (nm=10 -9 m) ν (s -1 or Hz) - frequency c =
Background image of page 9

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Use lasers to "clock the reaction: Detection (probe) laser beams is delayed by a period of 50-5,000 femtosecond with respect to excitation (pump) laser beam Each laser light pulse lasts about 100 fs
Background image of page 10
To study unimolecular reactions, Minimize collisions by working in high vacuum and beams of molecules
Background image of page 11

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 12
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 21

L8_atm_femto_115b08 - L8: Interaction of molecules with...

This preview shows document pages 1 - 12. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online