Pitt CHEM 1140 - Spectroscopy (34 pages)

Previewing pages 1, 2, 16, 17, 18, 33, 34 of 34 page document View the full content.
View Full Document

Spectroscopy



Previewing pages 1, 2, 16, 17, 18, 33, 34 of actual document.

View the full content.
View Full Document
View Full Document

Spectroscopy

70 views


Pages:
34
School:
University of Pittsburgh
Course:
Chem 1140 - Advanced Inorganic Laboratory

Unformatted text preview:

P Wipf 1 Chem 1140 Chem 1140 Spectroscopy UV VIS IR NMR UV VIS Spectroscopy The Absorption Laws I1 I0 I intensity of the incident beam Detector transmitted light Overall transmittance T Internal transmittance T i Usually T0 Ti I2 I2 I1 I I0 what is actually measured of interest to the spectroscopist Such differences as might exist can be minimized by using matched cells and setting T for the reference at 100 P Wipf 2 Chem 1140 The quantity I I0 is independent of the intensity I of the source and proportional to the number of absorbing molecules Lambert Beer Law log I0 I l c A l path length of the absorbing solution in cm c concentration in moles liter Log I0 I absorbance or optical density A molar extinction coefficient 1000 cm2 mol 1 i s a characteristic of a g iven compound or more accurately the light absorbing system of the compound the so called chromophore i s correlated to the size of the chromophore and of course wave length dependent f f c Approximation An accurate determination of r equires determining A at various concentrations 10 105 scales with extended systems dyes P Wipf 3 Chem 1140 UV Vis spectra are usually plotted as A vs plots A 2 hypsochromic hyperchromic shifts bathochromic hypochromic 1 n max nm Though there are discrete levels of electronic excited states in a molecule we do not observe absorption lines but broad peaks the change in vibrational and rotational energy levels during absorption of light leads to peaks containing vibrational and rotational fine structure Due to additional interaction with solvent molecules this fine structure is blurred out and a smooth curve is observed vapour phase one can observe vibrational fine structure P Wipf 4 Chem 1140 Selection Rules The irradiation of organic compounds may or may not give rise to excitation of electrons from one orbital to another orbital There are transitions between orbitals that are quantum mechanically forbidden Two selection rules Spin rule Symmetry rule n The total spin S may not



View Full Document

Access the best Study Guides, Lecture Notes and Practice Exams

Loading Unlocking...
Login

Join to view Spectroscopy and access 3M+ class-specific study document.

or
We will never post anything without your permission.
Don't have an account?
Sign Up

Join to view Spectroscopy and access 3M+ class-specific study document.

or

By creating an account you agree to our Privacy Policy and Terms Of Use

Already a member?