Lecture
This presentation is the property of its rightful owner.
Sponsored Links
1 / 23

Lecture 8 PowerPoint PPT Presentation


  • 52 Views
  • Uploaded on
  • Presentation posted in: General

Lecture 8. Detectors Spectrophotometer design Background correction Width of the spectral peak. Ch. 20 Harris. Monochromator (filter, wavelength selector). Light Source. Detector. Sample. Spectrometer. Data Processing. A phototube. K/Cs/Sb. GaAs. -. +. Ag/O/Cs. 90 V.

Download Presentation

Lecture 8

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


Lecture 8

Lecture 8

Detectors

Spectrophotometer design

Background correction

Width of the spectral peak

Ch. 20 Harris


Lecture 8

Monochromator

(filter,

wavelength selector)

Light Source

Detector

Sample

Spectrometer

Data Processing


Lecture 8

A phototube

K/Cs/Sb

GaAs

-

+

Ag/O/Cs

90 V

Wavelength, nm


Lecture 8

Photomultiplier

Several electrons

for each incident electron

Several electrons

for each photon

Quarz

envelope

Light, h

Photoemissive

cathode

Anode


Lecture 8

Photoelectromultiplier

dynode

dynode

electron

photon


Lecture 8

Single beam

Double beam


Lecture 8

Double beam with the beams separated in time


Lecture 8

Single beam design with

210-element area detector


Lecture 8

Flat background

Ipeak

I

Ipeak – I0

Intensities at two different

wavelengthes

Peak

I0

Baseline

wavelength


Lecture 8

Flat background

Ipeak

I

constant

Peak

First derivative eliminates

flat background

I0

Baseline

Wavelength (l)


Lecture 8

Linear Background

Ipeak

I

Ipeak – (I1+I2) / 2

I1

Background

I2





Wavelength (l)


Lecture 8

Linear Background

I

Ibackground = Kl+b

First:

Background

Second:

Second derivative eliminates

linear background

Wavelength (l)


Lecture 8

Original

Second

4th

First


Lecture 8

Well defined peaks and valleys

High noise

Some peaks visible

Almost featureless:

little information

Low noise


Lecture 8

Only photons of one specified wavelength are

absorbed

Excited state

Ground state


Lecture 8

Width

Velocity of a particle >1000 m/s

Doppler

Speed of light 300,000,000 m/s

collisions

Approximately as Doppler

Both effects increase with the temperature

and

decrease with the size of the molecule/atom

Width is around 0.01-0.001 nm in visible area

Multiple energy levels


Lecture 8

Energy levels

of excited state

Energy sublevels

Energy levels

of ground state


Lecture 8

A primitive rule:

Molecular spectra - widebands

Atomic spectra - narrowlines


  • Login