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IR spec

QuestionAnswer
Three main process on IR spec emission, absorption, reflection
Near Ir range and wave number range: 0.78-2.5; wavenumber 128800-4000
Mid Ir range and wave number range: 2.5-50; wavenumber 4000-200
far Ir range and wave number range: 50-1000; wavenumber 200-10
most used region range: 2.5-15; wavenumber 4000-670
relationship between wave number to energy and frequency E=hc/lamda=hv
types of molecular transitions stretching and bending
Vibrational modes translational motion- 3 degrees of freedom rotation about its center of gravity vibrational motion
Name sources for IR instrumentation nernst glower Globular Incandescent wire Mercury Arc Tungsten filament CO2 lase
IR instrumentation three types: 1. Dispersive grating spectrophotometer 2. Multiplexed instruments, e.g., Fourier transform IR 3. Non-dispersive photometer
three types of detectors in IR region 1.thermal 2. pyroelectric 3. photo-conducting
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.
Thermal detectors i)thermocouple ii) bolometer iii) Golay tube (pneumatic)
Dispersive IR Spectrophotometer double-beam;signal “chopping”;optical design and configuration;null type detector;limitations;
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
which of the sources are useful in all of the regions and has a positive temperature coefficient? Globar
which of the sources has the lowest intensity, and the longest life? Incandescent wire
Name solvents that can be used in IR-spec analysis carbon tetrachloride, chloroform, carbon disulfide.
Created by: K@t
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