Infrared Spectroscopy

Question 1

Explain Infrared Process

Answer 1

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

Question 2

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

Answer 2

varying electromagnetic field is produced

Question 3

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

Answer 3

more intense

Question 4

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

Answer 4

coupled; absorbed

Question 5

Coupled wave vibrates with ___ the amplitude

Answer 5

twice

Question 6

Types of bond stretching (2)

Answer 6

Symmetric and asymmetric

Question 7

Types of bond bending (4)

Answer 7

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

Question 8

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

Answer 8

vibrational mode

Question 9

Vibrational modes for
linear?
non linear?

Answer 9

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

x = number of atoms

Question 10

Basic Instrumentation (IR)

Answer 10

Radiation source
Sample Holder
Wavelength Selector (Monochromator)
Detector

Question 11

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

Answer 11

blackbody sources

Question 12

Common blackbody sources

Answer 12

Globar
Nernst Glower
Incandescent Wire Source

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

Question 13

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

Answer 13

Nernst Glower

Question 14

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

Answer 14

Globar

Question 15

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

Answer 15

incandescent wire source

Question 16

Blackbody source for far-infrared region

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

Answer 16

Mercury Arc Lamp

Question 17

CO2 laser consists of

Answer 17

70% He, 15% CO2, 15% N2

Question 18

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

Answer 18

alkali halides; NaCl, KBr, CaF2

Question 19

_____ solvents cannot be used because they cannot dissolve alkali halides

Answer 19

Aqueous solvents

Question 20

For most liquids, the sample cell thickness is ___

Answer 20

0.01-0.05 mm

Question 21

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

Answer 21

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

Question 22

Sample holder techniques for solid samples (4)

Answer 22

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

Question 23

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

Answer 23

Mull technique

Question 24

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

Answer 24

solid run in solution

Question 25

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

Answer 25

case film technique

Question 26

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

Answer 26

Pressed pellet technique

Question 27

Common wavelength selector for IR

Answer 27

reflective grating

Question 28

Why glass prism is not suitable for IR Spectroscopy

Answer 28

glass prism absorbs IR

Question 29

Detector for IR Spectroscopy (4)

Answer 29

Thermal detectors such as Thermocouple Bolometer Photoconducting Detectors Pyroelectric Detectors

Question 30

Types of Instruments (IR) (3)

Answer 30

Non-dispersive Dispersive Fourier Transform

Question 31

used to detect gas and measure concentration of carbon oxides

Answer 31

non-dispersive

Question 32

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

Answer 32

Dispersive

Question 33

FTIR is based on

Answer 33

Michelson Interferometer

Question 34

Advantages of FTIR from Normal IR (3)

Answer 34

Jacquinot advantage Connes advantage Felgett advantage

Question 35

Since the instrument have few optical elements and no slits to attenuate the radiation, the ___ reaching the detector is ____ What kind of advantage?

Answer 35

power of radiation; greater Jacquinot advantage.

Question 36

Type of advantage associated with extremely high wavelength accuracy and precision

Answer 36

Connes advantage

Question 37

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

Answer 37

Felgett advantage

Question 38

IR Techniques (3)

Answer 38

Specular Reflectance Diffuse Reflectance Attenuated Total Reflectance

Question 39

IRRAS

Answer 39

Infrared reflection absorption spectroscopy

Question 40

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

Answer 40

IRRAS

Question 41

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

Answer 41

IRRAS

Question 42

IRRAS advantages (2)

Answer 42

sensitivity to monolayer samples nondestructive analysis

Question 43

DRIFTS

Answer 43

Diffuse Reflectance Infrared Fourier Transform Spectroscopy

Question 44

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

Answer 44

DRIFTS

Question 45

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

Answer 45

Attenuated Total Reflectance

Question 46

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

Answer 46

Attenuated Total Reflectance

Question 47

used for shiny or rough surface

Answer 47

attenuated total

Question 48

used for shiny materials

Answer 48

specular reflectance

Question 49

used for rough surfaces

Answer 49

diffuse reflectance

Question 50

Qualitative Analysis (IR) (4)

Answer 50

General Scheme Group Frequency Region Fingerprint Region Computer Searches

Question 51

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

Answer 51

not directly

Question 52

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

Answer 52

many compounds have different IR spectra accuracy and precision