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Analytical Chemistry > Infrared Spectroscopy > Flashcards

Infrared Spectroscopy Flashcards

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1
Q

Explain Infrared Process

A

When a wave of infrared light (from spectrophotometer) encounters this oscillating EM field generated by the oscillating dipole of the same frequency, the two waves couple, and IR light is absorbed

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2
Q

As covalent bond oscillates due to oscillation of dipole of the molecule, ____ is produced

A

varying electromagnetic field is produced

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3
Q

The greater the dipole moment change through vibration, the ___ the EMF that is generated

A

more intense

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4
Q

when a wave of IR light encounters this oscillating EMF, the waves ___ and IR light is ___

A

coupled; absorbed

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5
Q

Coupled wave vibrates with ___ the amplitude

A

twice

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6
Q

Types of bond stretching (2)

A

Symmetric and asymmetric

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7
Q

Types of bond bending (4)

A

in-plane rocking
in-plane scissoring
out-of-plane wagging
out-of-plane twisting

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8
Q

a molecule can vibrate in many ways, and each way is called ___

A

vibrational mode

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9
Q

Vibrational modes for
linear?
non linear?

A

linear: 3x-5
nonlinear: 3x-6

x = number of atoms

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10
Q

Basic Instrumentation (IR)

A

Radiation source
Sample Holder
Wavelength Selector (Monochromator)
Detector

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11
Q

inert solid that is electrically heated to a temperature between 1500 to 2200 K

A

blackbody sources

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12
Q

Common blackbody sources

A

Globar
Nernst Glower
Incandescent Wire Source

*** (others)
CO2 laser
Mercury Arc Lamp
Tubgsten Halogen Lamp

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13
Q

:rare earth oxides (Ze, Ce, Th) heated electrically formed into a cylinder having a diameter of 1 to 2 mm
: with platinum leads

A

Nernst Glower

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14
Q

Balckbody source that uses silicon carbide rod; water cooling is needed; more expensive

A

Globar

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15
Q

Blackbody source that has lower intensity but longer life than globar and nernst glower

a tightly wound spiral of nichrome wore or rhodium-wire heated to about 1100K by an electrical current

A

incandescent wire source

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16
Q

Blackbody source for far-infrared region

quartz-jacketed tube containing mercury vapor at a pressure greater than one atmosphere

A

Mercury Arc Lamp

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17
Q

CO2 laser consists of

A

70% He, 15% CO2, 15% N2

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18
Q

Liquid sample cells can be sandwiched using liquid sample cells of highly purified ____, such as ___

A

alkali halides; NaCl, KBr, CaF2

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19
Q

_____ solvents cannot be used because they cannot dissolve alkali halides

A

Aqueous solvents

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20
Q

For most liquids, the sample cell thickness is ___

A

0.01-0.05 mm

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21
Q

Sample cell for gas samples is made up of and with path length of?

A

alkali halides such as NaCl, KBr
5-10 cm because of weak absorbance

22
Q

Sample holder techniques for solid samples (4)

A

Mull technique
Solid run in solution
case film technique
pressed pellet technique

23
Q

finely crushed sample is mixed with Nujol in a marble or agate mortar, with pestle to make a thick paste. a thin film is applied onto the salt plates and mounted in a path of IR beam

A

Mull technique

24
Q

A drop of solution is placed on the surface of alkali metal disc and solvent is evaporated to dryness leaving a thin film of solute

A

solid run in solution

25
Q

amorphous solid is deposited on surface of KBr or NaCl cell by evaporation of solution of solid; film is not too thick

A

case film technique

26
Q

small amount of finely ground solid sample is mixed with 100 times its weight of KBr and compressed into a thin transparent pellet

A

Pressed pellet technique

27
Q

Common wavelength selector for IR

A

reflective grating

28
Q

Why glass prism is not suitable for IR Spectroscopy

A

glass prism absorbs IR

29
Q

Detector for IR Spectroscopy (4)

A

Thermal detectors such as

Thermocouple
Bolometer
Photoconducting Detectors
Pyroelectric Detectors

30
Q

Types of Instruments (IR) (3)

A

Non-dispersive
Dispersive
Fourier Transform

31
Q

used to detect gas and measure concentration of carbon oxides

A

non-dispersive

32
Q

scanning instrument uses a grating monochromator to resolve the IR radiation into individual frequencies

A

Dispersive

33
Q

FTIR is based on

A

Michelson Interferometer

34
Q

Advantages of FTIR from Normal IR (3)

A

Jacquinot advantage
Connes advantage
Felgett advantage

35
Q

Since the instrument have few optical elements and no slits to attenuate the radiation, the ___ reaching the detector is ____

What kind of advantage?

A

power of radiation; greater

Jacquinot advantage.

36
Q

Type of advantage associated with extremely high wavelength accuracy and precision

A

Connes advantage

37
Q

Type of FTIR advantage: Since all elements of the source reach the detector simultaneously, an entire spectrum can be obtained in a brief period

A

Felgett advantage

38
Q

IR Techniques (3)

A

Specular Reflectance
Diffuse Reflectance
Attenuated Total Reflectance

39
Q

IRRAS

A

Infrared reflection absorption spectroscopy

40
Q

used for analysis of both organic and inorganic samples having large, flat, thin reflective surfaces

A

IRRAS

41
Q

measures the energy that is reflected off the surface of a sample (refractive index)

A

IRRAS

42
Q

IRRAS advantages (2)

A

sensitivity to monolayer samples
nondestructive analysis

43
Q

DRIFTS

A

Diffuse Reflectance Infrared Fourier Transform Spectroscopy

44
Q

useful for analysis of both organic and inorganic samples that can be ground into fine powder and mixed in a powder matrix such as KBr

A

DRIFTS

45
Q

useful for samples that are difficult to deal with such as solid of limited solubility, films, threads, etc

A

Attenuated Total Reflectance

46
Q

operates by measuring the changes that occur in an internally reflected IR beam when the beam comes into contact with sample

A

Attenuated Total Reflectance

47
Q

used for shiny or rough surface

A

attenuated total

48
Q

used for shiny materials

A

specular reflectance

49
Q

used for rough surfaces

A

diffuse reflectance

50
Q

Qualitative Analysis (IR) (4)

A

General Scheme
Group Frequency Region
Fingerprint Region
Computer Searches

51
Q

The area of an IR band (peak) is ____ to the concentration of functional groups producing the peak

A

not directly

52
Q

IR Spectroscopy has good selectivity since____ but not as good as UV/Vis in terms of ___

A

many compounds have different IR spectra

accuracy and precision

Analytical Chemistry (13 decks)

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