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This is project presentation for Physics course. Instructor and project supervisor was Prof. Alpana Vishvajit at Aliah University. It includes: Infrared, Spectroscopy, Molecular, Vibrations, Conditions, Absorption, Sources, Detectors, Radiation
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Solids, liquids, gases, semi-solids, powders, and polymers can be analyzed
Used for identification of unknowns and for confirming identities
Infrared spectrum is information rich; the peak positions, intensities, widths, and shapes in a spectrum all provide useful information
Peak intensities in an infrared spectrum are proportional to concentrations, so infrared spectra can be used to measure concentrations as well
Relatively fast, easy and inexpensive
A sample must contain chemical bonds to have an infrared spectrum; thus atoms or mono-atomic ions do not have infrared spectra
Homo-nuclear diatomic molecules do not possess infrared spectra due to their symmetry
Infrared spectroscopy works best on pure substances. For mixtures, the spectrum will be complex and it will be hard to know which infrared bands are due to which molecule
Aqueous solutions are also difficult to analyze using infrared spectroscopy
The molecule must have a vibration during which the change in dipole moment with respect to distance is non-zero
Where; = change in dipole moment, = change in bond distance
Vibrations that satisfy this equation are said to be infrared active and those which do not, are called infrared inactive
Infrared bands due to vibrations for which is large will be more intense than bands due to vibrations for which is small
x ^0
x
The H-Cl stretch of hydrogen chloride
is an example of infrared active vibration; the molecule vibrates at the same frequency as light
The symmetric stretch of carbon
dioxide can not be excited by infrared radiation and can not give rise to a band in the infrared spectrum of the molecule
The positions of mid-infrared (MIR) fundamental bands correlate well with molecular structure, which is why the MIR part of the electromagnetic spectrum is so useful
Overtones can be recognized because they are often at about twice the wavenumber of a fundamental band and appear mostly in the NIR region (0.78 to 2.5 μm)
Overtones give rise to very weak absorbance bands and provide little information about the molecular structure
A ν = 0 to ν = 2 transition is typically 10 times weaker than a fundamental band; a ν = 0 to ν = 3 transition is typically 100 times weaker than a fundamental band (^10)
The infrared spectrum of a sample is recorded by passing a beam of infrared light through the sample
Examination of the transmitted light reveals that how much energy was absorbed at each wavelength
Thermal detectors do not require cooling, but have disadvantages that response time is slow and detection capability is low
Quantum detectors offer higher detection performance and a faster response speed, although their photosensitivity is dependent on wavelength
Quantum detectors must be cooled for accurate measurement, except for detectors used in the NIR region (^13)
Type No.
Measurement Temperature T (C^0 )
Spectral response range λ (μm)
Peak sensitivity wavelength λ p (μm)
Photo sensitivity S ( λ=λ p) (A/W)
Detectability D*^ ( λ=λ p ) (cm-Hz1/2/W)
NEP λ=λ p (W/Hz1/2) G6742-
25
0.9 – 1.7 1.55 0.95 5 x 10^12
2 x 10- G6742-003 4 x 10- G6849 2 x 10- G6849-01 1 x 10- G6854-01 (^) 2 x 10- G7150-16 2 x 10- G7151-16 3 x 10- G8421- 0.9 – 1.9 1.75 1.1 5 x 10^11
9 x 10- G8421-05 1.5 x 10- G8371-01 2 x 10- G8371-03 8 x 10- G8422- 0.9 – 2.1 1.95 1.2 2.5 x 10^11
1.5 x 10- G8422-05 2.5 x 10- G8372-01 4 x 10- G8372-03 1.5 x 10- G8423- 1.2 – 2.6 2.3 1.1 5 x 10^10
7 x 10- G8423-05 1 x 10- G8373-01 2 x 10- G8373-03 8 x 10docsity.com-12^16
0.0 900 1100 1300 1500 1700
974
1163
NIR absorption spectrum of liquid hydrogen peroxide using tungsten-halogen light source (LS-1-Cal), Integration time=3.6 sec September 1, 2010
Absorbance (a.u)
Wavelength (nm) 20
11 10 9 8 7 6
0
20
40
60
80
100
10271
8600
NIR transmission spectrum of liquid hydrogen peroxide using tungsten-halogen light source (LS-1-Cal), Integration time=3.6 sec September 1, 2010
Transmittance (%)
Wavenumber (cm-1) / 10^3
