(a) Interpretation: For an angle of incidence of 45 0 , the effective penetration depth of the evanescent wave should be determined. Penetration depth if the angle changed to 60 0 should be determined. Concept introduction: The effective penetration depth can be calculated as follows: d p = λ c 2 π [ sin 2 θ − ( n s / n c ) 2 ] 1 / 2 Here, d p − effective penetration depth λ c − Wavelength of the beam θ − incident angle n s − refractive index of the sample n c − refractive index of the crystal

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Principles of Instrumental Analysis

7th Edition
Douglas A. Skoog + 2 others
Publisher: Cengage Learning
ISBN: 9781305577213
BuyFind

Principles of Instrumental Analysis

7th Edition
Douglas A. Skoog + 2 others
Publisher: Cengage Learning
ISBN: 9781305577213

Solutions

Chapter 17, Problem 17.13QAP
Interpretation Introduction

(a)

Interpretation:

For an angle of incidence of 450, the effective penetration depth of the evanescent wave should be determined. Penetration depth if the angle changed to 600 should be determined.

Concept introduction:

The effective penetration depth can be calculated as follows:

dp=λc2π[sin2θ(ns/nc)2]1/2

Here,

dp effective penetration depthλc Wavelength of the beamθ incident anglens refractive index of the samplencrefractive index of the crystal

Interpretation Introduction

(b)

Interpretation:

The penetration depths for sample refractive indexes varying from 1.00 to 1.70 in steps of 0.10 should be determined. Penetration depth should be plotted as a function of refractive index. The refractive index for which the penetration depth becomes zero should be determined.

Concept introduction:

dp=λc2π[sin2θ(ns/nc)2]1/2dp effective penetration depthλc Wavelength of the beamθ incident anglens refractive index of the samplencrefractive index of the crystal

Interpretation Introduction

(c)

Interpretation:

For a sample with a refractive index 1.37 at 2000 cm-1 and incident angle of 450, the penetration depth versus the ATR crystal refractive index should be plotted.

Concept introduction:

The effective penetration depth can be calculated as follows:

dp=λc2π[sin2θ(ns/nc)2]1/2

Here,

dp effective penetration depthλc Wavelength of the beamθ incident anglens refractive index of the samplencrefractive index of the crystal

Interpretation Introduction

(d)

Interpretation:

The effective penetration depth at 3000 cm-1, 2000 cm-1 and 2000 cm-1 should be determined.

Concept introduction:

The effective penetration depth can be calculated as follows:

dp=λc2π[sin2θ(ns/nc)2]1/2

Here,

dp effective penetration depthλc Wavelength of the beamθ incident anglens refractive index of the samplencrefractive index of the crystal

Interpretation Introduction

(e)

Interpretation:

The principles of the new method to obtain a depth profile of a sample surface using ATR spectroscopy should be described.

Concept introduction:

In ATR spectroscopy through the ATR crystal, an infrared beam is passed such that it reflects off the internal surface at least once when in contact with the sample. This reflection results in an evanescent wave which goes into the sample. The penetration depth is determined by the wavelength of IR beam, angle of incidence, refractive indexes of sample and the crystal.

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