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Molecular Spectroscopy - Advanced Analytical Chemistry - Lecture Slides, Slides of Analytical Chemistry

Indicator Electrodes, Potentiometry, Electrochemistry, Electrode Kinetics, Electrogravimetry, Polarography, Square Wave Voltammetry, Wavelength Selection, Types of Spectroscopy, Detectors, Theory of Molecular Absorption, Absorption by Organic Molecules, Applying UV-vis Spectroscopy are major topics of this course. Main points from these slides are: Molecular Spectroscopy, Spectroscopy, Electromagnetic Radiation, Refractive Index, Wavelength, Speed of Light, Polarizability, Refractive Indices, Re

Typology: Slides

2012/2013

Uploaded on 08/30/2013

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Molecular Spectroscopy

Spectroscopy

(^) = methods based on the

(EM) and matterinteraction of electromagnetic radiation

Electromagnetic Radiation = form of energy with both wave and particle properties

EM moves through space as a wave

terms of electric vectorbest understood inEM with matter are Most interactions of

Dispersion CurveA Typical

showing

(^) η (^) as

frequencya function of

(^) ν

( νννν )

(η)

Normally

(^) η (^) increases with

(^) ν (^) and this is

referred to as “Normal Dispersion”

When absorption occurs, the nature of the interaction changes

η slows downelectric vector interacts with the medium &^ is a measure of the extent to which the

For a given frequency and medium, a larger η (^) means more interaction with electric field

polarizability & the medium is said to have greater

(^) i.e., is more able to follow

the electric vector

Dispersion CurveA Typical η 2) regions where ν increases with absorbtion bandprior to an

This is referred to as normal dispersion

( νννν )

(η)

Dispersion CurveA Typical η 3) regions where ν decreases with absorption bandsvery sharply at

because the nature of the interaction changesThis is referred to as anomalous dispersion

( νννν )

(η)

Refractive indices (

η ) for various substances at

589 nm (the sodium D line)

Substance

η

air

water, 20

(^) o C

NaCl crystal

benzene

quartz (fused)

glass (crown)

ethyl alcohol

carbon disulfide

Refraction

(^) = change in velocity of EM as it

goes from one medium to another

to surfaceNormal

Velocity largerMedium 1 (air)

(^) η (^) = 1.

Velocity smallerMedium 2 (glass)

(^) η (^) = 1.

rayIncident

Ф 1 Ф 2

ray Refracted

directionOriginal

normalRay bent toward

Critical Angle

Ф

C )

to surface Normal

Medium 2 (glass)Medium 1 (air)

90 ray isIncident o to

grazing incidencethis is callednormal

Ф 1 Ф 2

ray Refracted

Maximum value of

(^) Ф 2

Ф (^2) = (^) Ф C At 90

o incidence sin

(^) Ф (^1) = 1.

η 1

sin (^) Ф C = ----- η 2

  1. Fiber Optics1) RefractometersImportant for:
  • waves must have similarWave Interaction - interaction between waves

(^) ν (^) but can be out of

phase (i.e., they start in different places)

  • wave yPrinciple of superposition = vectors add

(^1) +y

2 formed by adding y

1 & y

2 by

vector addition

Interference

(^) - amplitude of the resulting

wave depends on phase difference

(^) α (^1)

α 2

⇒Interference Constructive waves add

Destructive Interference

(^) ⇒

(^) waves cancel

At (^) α (^1)

α (^2) = 0

o adding of waves gives

Maximum Constructive Interference

(^0) o

180 o 360 o 540 o 720 o 900 o

is zeroWave 1 & Wave 2difference betweenPhase angleResultant waveWave 2Wave 1

(^) α (^1)

α (^2) = 0 o

Amplitude

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When

(^) α (^1)

α (^2) = 180

o or 540

o adding of waves

gives Maximum Destructive Interference

(^0) o

180 o 360 o 540 o 720 o 900 o

Resultant waveWave 2 Wave 1

is 180Wave 1 & Wave 2difference betweenPhase angle

o (α (^1)

α (^2) = 180

)o

Amplitude

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Fourier Analysis

(^) – mathematical process of

various component frequencies.and a computer to figure out amplitudes ofNMR. Requires complex mathematicsTransform (FT) methods like FTIR and FTintegral and is important in all Fourierfrequencies. This requires a Fouriervarious frequencies into their individualresolving a combination of waves of