IR spec
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| Three main process on IR spec | emission, absorption, reflection
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| Near Ir range and wave number | range: 0.78-2.5; wavenumber 128800-4000
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| Mid Ir range and wave number | range: 2.5-50; wavenumber 4000-200
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| far Ir range and wave number | range: 50-1000; wavenumber 200-10
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| most used region | range: 2.5-15; wavenumber 4000-670
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| relationship between wave number to energy and frequency | E=hc/lamda=hv
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| types of molecular transitions | stretching and bending
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| Vibrational modes | translational motion- 3 degrees of freedom
rotation about its center of gravity
vibrational motion
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| Name sources for IR instrumentation | nernst glower
Globular
Incandescent wire
Mercury Arc
Tungsten filament
CO2 lase
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| IR instrumentation | three types:
1. Dispersive grating spectrophotometer
2. Multiplexed instruments, e.g., Fourier transform IR
3. Non-dispersive photometer
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| three types of detectors in IR region | 1.thermal
2. pyroelectric
3. photo-conducting
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| Can homonuclear molecules absorb IR readiation? | homonuclear molecules, e.g., O2, Cl2. N2 and chiral molecules in the crystalline state have no net change in dipole moment during their vibration or rotation, thus these molecules cannot absorb IR radiation.
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| Thermal detectors | i)thermocouple
ii) bolometer
iii) Golay tube (pneumatic)
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| Dispersive IR Spectrophotometer | double-beam;signal “chopping”;optical design and configuration;null type detector;limitations;
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| which of the sources are useful in near- and mid IR regions; not used in the far Ir regions and has a large negative temperature coefficient? | Nernst Glower
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| which of the sources are useful in all of the regions and has a positive temperature coefficient? | Globar
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| which of the sources has the lowest intensity, and the longest life? | Incandescent wire
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| Name solvents that can be used in IR-spec analysis | carbon tetrachloride, chloroform, carbon disulfide.
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Created by:
K@t
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