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Intro to Spectrometric Methods - Analytical Chemistry II - Lecture Slides, Slides of Analytical Chemistry

Major topics of this course are: General Instrumentation, Spectroscopy Theory, Molecular Spectroscopy, Chromatography, Electrochemistry, Coulometric Methods, Voltammetric Methods. This lecture covers following points: Intro to Spectrometric Methods, Electromagnetic Radiation, Quantum-Mechanical Properties, Spectrochemical Measurements, Spectroscopy, Frequency, Amplitude, Angular Frequency, Phase Angle, Refraction

Typology: Slides

2012/2013

Uploaded on 08/30/2013

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Intro to Spectrometric Methods
General Properties of Electromagnetic
Radiation (EM)
Wave Properties of EM
Quantum-Mechanical Properties of EM
Quantitative Aspects of
Spectrochemical Measurements
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Download Intro to Spectrometric Methods - Analytical Chemistry II - Lecture Slides and more Slides Analytical Chemistry in PDF only on Docsity!

  • General Properties of ElectromagneticIntro to Spectrometric Methods Radiation (EM)
  • Quantitative Aspects of• Quantum-Mechanical Properties of EM• Wave Properties of EM Spectrochemical Measurements

R O Y

G

B V

SpectroscopyRayGamma

FluorescenceAbsorption,X-Ray

FluorescenceAbsorption,UV-vis

SpectroscopyAbsorptionInfrared

SpectroscopyAbsorptionMicrowave

EPRNMR

Transitions Nuclear

ElectronsInner Shell

ElectronsOuter Shell

VibrationsMolecular

RotationsMolecular

EnergyLow StatesSpin

EnergyHigh

Relationship between various wave properties

C

i

i

Where

(^) = frequency in cycles/s or Hz

i = wavelength in medium i

i = refractive index of medium i

C

(^) = speed of light in vacuum

(^) (2.99 x

(^1) 0 (^10) cm/s)^

EM slows down in media other than vacuum because medium (matter)electric vector interacts with electric fields in the

(^)  (^) this effect is greatest in solids &

liquids, in gases (air) velocity similar to vacuum

Wave Equation

y = A sin (

ω t + (^) α )

Where

ω A = amplitude (^) = angular frequency

α t = time (^) = phase angle

For a collection of waves the resulting y = Aposition y at a given t can be calculated by

(^1) sin (

ω (^1) t +

(^) α

(^1) ) + A

(^2) sin (

ω (^2) t +

(^) α

(^2) ) + …

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

Wave

(^1)

Wavedifference betweenPhase angleResultant wave Wave 2

(^1) (^) & Wave 2

is zero

(^) α (^1)

α (^2) = 0 o

Amplitude

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When

(^) α (^1)

α (^2) = (^1) 80 o or 540

o adding of waves

gives Maximum Destructive Interference

(^0) o

(^180) o 360 o 540 o 720 o 900 o

Wave

(^1)

Resultant wave Wave 2

Wavedifference betweenPhase angle

(^1) (^) & Wave 2

is (^1) 80 o (α (^1)

α (^2) = (^1) 80 )o

Amplitude

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Refraction

(^) = change in velocity of EM as it

goes from one medium to another

to surfaceNormal

Medium

(^1) (^) (air)

Velocity larger

(^) η (^) = (^1) .

Velocity smallerMedium 2 (glass)

(^) η (^) = (^1) .

rayIncident

Ф 1 Ф 2

ray Refracted

directionOriginal

normalRay bent toward

sin Equation for Refraction (Snell) (^) Ф 1

ν (^1)

η (^2)

if medium

η 2

sin

(^) Ф (^2)

ν (^2)

η (^1)

is air

(^) η (^1) = (^1) .

Magnitude of the direction change (i.e., size of equation asthe angle depends on wavelength (shown in

(^) ν ) this is how a prism works

Direction of bending depends on relative values of

(^) η (^) for each medium. Going from

low

(^) η (^) to higher, the ray bends toward the

normal. Going from higher

(^) η (^) to lower the ray

bends away from the normal.

rI

(η (^2)

η (^1) ) 2

Reflectance = R =

i I

(η (^2)

(^) η (^1) ) 2

Where I

i (^) and I

r = incident & reflected intensity

For radiation going from air (

η (^) = (^1) .00) to glass

(η (^) = (^1) .50) as shown in previous slide

R = 0.04 = 4 %

Many surfaces at 4 % each (i.e., many lenses) can generatescause serious light losses in a spectrometer. This

(^) stray radiation

(^) or

(^) stray light

.

Scattering

(^) = EM interacts with matter and changes

direction, usually without changing energy

This can be described using both the wave or

particle nature of light:

1 ) charge of matterWave – EM induces oscillations in electrical

⇒⇒^ ⇒⇒ (^) resulting in oscillating

in all directions = scattered radiationdipoles which in turn radiate secondary waves

matter to form a virtual state (lifetimeParticle (or Quantum) – EM interacts with

(^1) 0

  • 1 (^4) s)

which reemits in all directions.

Raman effect = when some molecules return to a

different state

(^) ⇒

(^) change in frequency

Rayleigh Scattering – scattering by particles whose longest dimension is < 5 % to

of (^) λ (^) with no change in observed frequency

(^) π (^4) α 2

sI (^) = ------------ (

(^) + cos

(^2) θ ) I o

λ (^4) r 2

polarizability

intensityscattering

wavelength

beam& scatteredincident beamangle between

to detectorscattering centerdistance from

intensityincident beam

short wavelengths are scattered more efficientlyNotice the fourth power dependence on wavelength meaning

(^) ⇒

(^) sky is blue

Polarizability (

α ) is measure of how well a given

frequency induces a dipole in a substance

α proteins)^ Tends to be large for large molecules (e.g.,

Large Particle Scattering – particle dimensions <

(^1) 0

% (^) λ (^) to (^1) . (^) λ

Applies in techniques like turbidimetry and nephelometry

Large particles do not act as a point source & give rise to various interference phenomena

Forward scatter becomes greater than back scatter

Linearly polarized light oscillates in one plane only as it moves through space

Linearly polarized light oscillates in one plane only as it moves through space

at 90polarized and H vector is Here E vector is vertically

o in horizontal plane