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Analytical Chemistry > Optical Spectroscopy > Flashcards

Optical Spectroscopy Flashcards

1
Q

Instruments for ____ include instruments which detect UV, visible, and IR regions of spectrum.

A

Optical Spectroscopy

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2
Q

___ and ____ instruments are not technically optical techniques, since ____

A

UV and IR
human eye is not sensitive to both, and they are outside visible region

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3
Q

Instrument Components (5)

A

Radiation Source
Wavelength Selector
Sample Holder
Detector
Signal processor and readout

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4
Q

Describe absorption measurements process

A

source > wavelength selector > sample > detector > signal processor and readout

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5
Q

Describe fluorescence measurements process

A

source > wavelength selector > sample > wavelength selector > detector > sign processor and readout

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6
Q

Describe emission measurements process

A

Source and sample > wavelength selector > detector> signal processor and readout

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7
Q

Generate a beam of radiation that is stable and has sufficient power at the desired wavelength

A

Radiation source

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8
Q

Types of Radiation Sources (2)

A

Continuum Sources
Line Sources

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9
Q

Emit radiation over a broad wavelength range and the intensity of the radiation changes slowly as a function of wavelength

A

Continuum Sources

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10
Q

Most common UV source

A

Deuterium lamp

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11
Q

Most common visible source

A

Tungsten lamp

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12
Q

Common sources for IR instruments

A

Glowing inert solids

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13
Q

Used when an intense source is required (fluorescence)

A

High pressure, gas filled (argon, xenon, mercury) lamps

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14
Q

emit a limited number lines or bands of radiation at specific wavelengths

A

Line Sources

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15
Q

Types of line sources (3)

A

Hollow cathode lamps
Electrodeless discharge lamps
Lasers

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16
Q

Light amplification by stimulated emission of radiation

A

Lasers

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17
Q

device that isolates restricted region of the electromagnetic spectrum used for measurement

A

Wavelength Selector

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18
Q

limited, narrow, continuous group of wavelengths

A

band

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19
Q

measures the quality of wavelength selector

A

inverse of the effective bandwidth

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20
Q

peak width at half height of a plot of the output of a wavelength selector (%T) as a function of wavelength

A

effective bandwidth

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21
Q

Types of Wavelength Selector (2)

A

Filter
Monochromator

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22
Q

used when there is only one wavelength of interest

device that selectively transmit light of different wavelengths

A

Filter

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23
Q

Designed for spectral scanning and used in most scanning spectrometers (UV, vis, IR)

A

Monochromator

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24
Q

Types of Filter (2)

A

Interference filter
Absorption filter

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25
Q

works in interference phenomenon, causes rejection of unwanted wavelength by selective reflection

A

Interference filter

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26
Q

functions by absorbing unwanted wavelengths and transmit the required wavelengths

A

absorption filter

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27
Q

rely on constructive and destructive interference in order to select a narrow bandwidth of radiation

A

interference filter

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28
Q

radiation will only pass through the interference filter if?

A

constructive interference occurs

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29
Q

consists of a pair ir mirrored, partially transparent plates separated by a wedge-shape layer of dielectric material

A

Interference wedge

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30
Q

among a growing repertoire of optical devices and materials that have resulted from the broad availability of laser technology

A

Holographic filter

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31
Q

a laser beam is split into two beams, which are directed by mirrors to recombine at the surface of a photosensitive film

A

Holographic filter

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32
Q

Types of absorption filter (2)

A

Glass filter
Gelatin filter

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33
Q

cut-off filters have ___ transmittance over a visible region and rapidly fall off to ___

A

100 to 0 percent

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34
Q

often ___ absorption filter are paired to give a narrower band of transmittance

A

two

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35
Q

made of solid sheet of glass that has been colored by pigments which is dissolved or dispersed in glass

A

Glass filter

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36
Q

Prepared by adding organic pigment in gelatin sheets

A

Gelatin filter

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37
Q

Why are gelatin filters not used nowadays?

A

tend to deteriorate with time
gets affected by heat and moisture

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38
Q

transmit a narrow band of wavelength of radiation

A

monochromator

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39
Q

Parts of Monochromator (5)

A

Entrance Slit
Collimating Lens or Mirror
Prism or Grating
Focusing Lens or Mirror
Exit Slit

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40
Q

provides rectangular optical image of the incoming polychromatic radiaiton

A

entrance slit

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41
Q

provides a parallel beam of radiation that impinges upon the dispersive element

A

collimating lens or mirror

42
Q

dispersive component

A

prism or grating

43
Q

focuses the dispersed radiation on the exit slit

A

focusing lens or mirror

44
Q

isolated the wavelength band of interest

45
Q

Types of Monochromator (2)

A

Prism and Grating

46
Q

Made of glass, quartz, fused silica

A

Prism monochromator

47
Q

When white light is passed through glass prism, ____

A

dispersion of polychromatic light in rainbow occurs

48
Q

By rotation of the prism, ____ can be made to pass through in the exit slit

A

different wavelengths of spectrum

49
Q

Dispersion and wavelength relationship

A

Dispersion increases as wavelength shortens (nonlinear)

50
Q

most effective in converting a polychromatic light to monochromatic light with a resolution of 0.1 nm

A

Grating Monochromator

51
Q

Higher and linear dispersion compared to prism monochromator

A

Grating Monochromator

52
Q

Types of Grating Monochromator (2)

A

Diffraction grating
Transmission grating

53
Q

more refined dispersion of light is obtained; large number of parallel line (grooves) on highly polished surface of aluminum

A

Diffraction grating

54
Q

Refraction takes place instead of reflection that produces reinforcement

A

Transmission grating

55
Q

Gives linear function of dispersion as a function of wavelengths

A

Grating Monochromator

56
Q

Type of diffraction grating characterized by a relatively low groove density, but a groove shape which is optimized for use at high incidence angles and therefore high diffraction orders

A

Echelle grating

57
Q

Type of diffraction grating with a grooved or blazed mirror that has relatively broad faves upon which reflection occurs and narrow unused faces

A

Echellete or blazed grating

58
Q

Major difference between echelle and echellette gratings

A

Echelle gratings have fewer blazings (grooves) than Echellette gratings

59
Q

Two pieces of carefully machined metal to give sharp edges that are exactly parallel to one another

A

Monochromator Slit

60
Q

Slits are commonly connected to ___ mechanism so the slit width can be adjusted

A

micrometer mechanism

61
Q

The effective bandwidth of a wavelength selector is the ____ of the band of the radiation in wavelength units at ____

A

width
half-peak height

62
Q

For qualitative analysis, slit width is ___ in order to resolve narrow peaks

63
Q

For ___ analysis, slit widths are increased to improve the light gathering power or intensity of the output radiation

A

Quantitative analysis

64
Q

Another important method to detect a spectrum without the need of separating wavelengths

A

Interferometry

65
Q

uses interference of light to record a spectrum

A

interferometry

66
Q

Converts the radiant energy into a usable signal (electricity)

67
Q

Early detectors in spectroscopic instruments (3)

A

human eye or photographic plates or films

68
Q

General types of radiation transducers (2)

A

Photon detectors
Thermal detectors

69
Q

Photon detectors (7)

A

Vacuum phototubes
Photomultiplier tubes
Photovoltaic cells
Silicon photodiodes
Photoconducting detector
Diode array
Others

70
Q

Composed of semicylindrical cathode and a wire anode inside of an evacuated, transparent tube

A

Vacuum Phototubes

71
Q

The cathode in vacuum phototubes is coated with ____ that emits electrons when ____

A

photoemissive material (Ga/As)
struck by EM radiation

72
Q

By applying a potential across the cathode and anode, the electrons will flow from _____ resulting in a ____

A

cathode to anode
photocurrent

73
Q

The photocurrent is ___ and sent to a ____

A

amplified and sent to a readout device

74
Q

The power of incident radiation impinging upon cathode is ____ to the current of electrons induced in the phototube

A

directly proportional

75
Q

Useful for measurement of low radiant powers (weak light signal)

contains dynodes

A

Photomultiplier Tube

76
Q

Constructed of a semiconducting later (Se) deposited on an Fe or Cu cathode and the semiconductor is coated with a thin metallic layer (Au or Ag) which serves as anode

A

Photovoltaic Cell

77
Q

When radiation reaches the semiconductor, ____ are broken resulting in ____

A

covalent bonds are broken resulting in conduction electrons and holes

78
Q

Electron flow in Photovoltaic Cell

A

Anode (metallic layer) to cathode (semiconductor)

79
Q

thin film of semiconductor material

absorption of radiation by these materials promotes nonconducting valence electrons to higher energy conducting state, thus ____

A

Photoconductive Detector
decreasing the electrical resistance of the semiconductor

80
Q

Types of Photoconductive Detector (2)

A

PbS photon detector
HgCd telluride detector

81
Q

photoconductive detector used near IR

A

PbS photon detector

82
Q

photoconductive detector used for mid and far IR region; cooled with liquid N2, also finds widespread use in FTIR

A

HgCd telluride detector

83
Q

Consists of a reverse-biased pn junction on a silicon chip

A

Silicon Photodiode

84
Q

Multi-channel detector made up of an array of photosensitive silicon diodes on a single silicon chip

A

Diode Array Detector

85
Q

eliminates the need for a monochromator

A

Diode Array Detector

86
Q

Measures the heat induced by the impinging radiation

A

Thermal detectors

87
Q

Thermal detectors are used for _____ because ____

A

infrared spectroscopy
photons in IR lack the energy to cause photoemission of electrons

88
Q

Types of thermal detectors (4)

A

Thermocouples
Bolometers
Pyroelectric transducers
Pneumatic cells

89
Q

Consists of a pair of junctions formed when two pieces of metal such as bismuth are fused to either end of a dissimilar metal such as antimony

A

Thermocouple

90
Q

Thermocouple has ___ response time

91
Q

Thermocouple is more common in older scanning IR instruments but ___

A

not well suited for FT-IR

92
Q

type of resistance thermometer constructed of strips of metals such as platinum or nickel or from a semiconductor which provides an electrical signal as a result of the variation in resistance of a conductor with temperature

93
Q

incident radiation is absorbed and heats up a thermal mass which is connected to a reservoir of constant temperature through a link with thermal conductance whose temperature increase is measured with a resistive thermometer

94
Q

bolometer is very sensitive to ____ and are predominantly used in IR between ___

A

thermal radiation
10 to 5000 μm

95
Q

detect photons through the heat they generate and the subsequent voltage generated in pyroelectric materials

A

Pyroelectric Detector

96
Q

Insulators with very special thermal and electrical properties

A

crystalline wafers (triglycine sulfate TGS) of pyroelectric materials

97
Q

takes place when an electric field is applied across a dielectric material

A

electric polarization

98
Q

Even after removal of the field, they retain a ___

A

temperature-dependent polarization

99
Q

TGS crystals have ___ response time and are _____ as detectors for FT-IR

A

fast
suitable and common

100
Q

FT-IR Spectroscopy
TGS

A

Fourier transform Infrared Spectroscopy
Triglycine Sulfate

Analytical Chemistry (13 decks)

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