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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
works in interference phenomenon, causes rejection of unwanted wavelength by selective reflection
Interference filter
26
functions by absorbing unwanted wavelengths and transmit the required wavelengths
absorption filter
27
rely on constructive and destructive interference in order to select a narrow bandwidth of radiation
interference filter
28
radiation will only pass through the interference filter if?
constructive interference occurs
29
consists of a pair ir mirrored, partially transparent plates separated by a wedge-shape layer of dielectric material
Interference wedge
30
among a growing repertoire of optical devices and materials that have resulted from the broad availability of laser technology
Holographic filter
31
a laser beam is split into two beams, which are directed by mirrors to recombine at the surface of a photosensitive film
Holographic filter
32
Types of absorption filter (2)
Glass filter Gelatin filter
33
cut-off filters have ___ transmittance over a visible region and rapidly fall off to ___
100 to 0 percent
34
often ___ absorption filter are paired to give a narrower band of transmittance
two
35
made of solid sheet of glass that has been colored by pigments which is dissolved or dispersed in glass
Glass filter
36
Prepared by adding organic pigment in gelatin sheets
Gelatin filter
37
Why are gelatin filters not used nowadays?
tend to deteriorate with time gets affected by heat and moisture
38
transmit a narrow band of wavelength of radiation
monochromator
39
Parts of Monochromator (5)
Entrance Slit Collimating Lens or Mirror Prism or Grating Focusing Lens or Mirror Exit Slit
40
provides rectangular optical image of the incoming polychromatic radiaiton
entrance slit
41
provides a parallel beam of radiation that impinges upon the dispersive element
collimating lens or mirror
42
dispersive component
prism or grating
43
focuses the dispersed radiation on the exit slit
focusing lens or mirror
44
isolated the wavelength band of interest
exit slit
45
Types of Monochromator (2)
Prism and Grating
46
Made of glass, quartz, fused silica
Prism monochromator
47
When white light is passed through glass prism, ____
dispersion of polychromatic light in rainbow occurs
48
By rotation of the prism, ____ can be made to pass through in the exit slit
different wavelengths of spectrum
49
Dispersion and wavelength relationship
Dispersion increases as wavelength shortens (nonlinear)
50
most effective in converting a polychromatic light to monochromatic light with a resolution of 0.1 nm
Grating Monochromator
51
Higher and linear dispersion compared to prism monochromator
Grating Monochromator
52
Types of Grating Monochromator (2)
Diffraction grating Transmission grating
53
more refined dispersion of light is obtained; large number of parallel line (grooves) on highly polished surface of aluminum
Diffraction grating
54
Refraction takes place instead of reflection that produces reinforcement
Transmission grating
55
Gives linear function of dispersion as a function of wavelengths
Grating Monochromator
56
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
Echelle grating
57
Type of diffraction grating with a grooved or blazed mirror that has relatively broad faves upon which reflection occurs and narrow unused faces
Echellete or blazed grating
58
Major difference between echelle and echellette gratings
Echelle gratings have fewer blazings (grooves) than Echellette gratings
59
Two pieces of carefully machined metal to give sharp edges that are exactly parallel to one another
Monochromator Slit
60
Slits are commonly connected to ___ mechanism so the slit width can be adjusted
micrometer mechanism
61
The effective bandwidth of a wavelength selector is the ____ of the band of the radiation in wavelength units at ____
width half-peak height
62
For qualitative analysis, slit width is ___ in order to resolve narrow peaks
narrow
63
For ___ analysis, slit widths are increased to improve the light gathering power or intensity of the output radiation
Quantitative analysis
64
Another important method to detect a spectrum without the need of separating wavelengths
Interferometry
65
uses interference of light to record a spectrum
interferometry
66
Converts the radiant energy into a usable signal (electricity)
Detector
67
Early detectors in spectroscopic instruments (3)
human eye or photographic plates or films
68
General types of radiation transducers (2)
Photon detectors Thermal detectors
69
Photon detectors (7)
Vacuum phototubes Photomultiplier tubes Photovoltaic cells Silicon photodiodes Photoconducting detector Diode array Others
70
Composed of semicylindrical cathode and a wire anode inside of an evacuated, transparent tube
Vacuum Phototubes
71
The cathode in vacuum phototubes is coated with ____ that emits electrons when ____
photoemissive material (Ga/As) struck by EM radiation
72
By applying a potential across the cathode and anode, the electrons will flow from _____ resulting in a ____
cathode to anode photocurrent
73
The photocurrent is ___ and sent to a ____
amplified and sent to a readout device
74
The power of incident radiation impinging upon cathode is ____ to the current of electrons induced in the phototube
directly proportional
75
Useful for measurement of low radiant powers (weak light signal) contains dynodes
Photomultiplier Tube
76
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
Photovoltaic Cell
77
When radiation reaches the semiconductor, ____ are broken resulting in ____
covalent bonds are broken resulting in conduction electrons and holes
78
Electron flow in Photovoltaic Cell
Anode (metallic layer) to cathode (semiconductor)
79
thin film of semiconductor material absorption of radiation by these materials promotes nonconducting valence electrons to higher energy conducting state, thus ____
Photoconductive Detector decreasing the electrical resistance of the semiconductor
80
Types of Photoconductive Detector (2)
PbS photon detector HgCd telluride detector
81
photoconductive detector used near IR
PbS photon detector
82
photoconductive detector used for mid and far IR region; cooled with liquid N2, also finds widespread use in FTIR
HgCd telluride detector
83
Consists of a reverse-biased pn junction on a silicon chip
Silicon Photodiode
84
Multi-channel detector made up of an array of photosensitive silicon diodes on a single silicon chip
Diode Array Detector
85
eliminates the need for a monochromator
Diode Array Detector
86
Measures the heat induced by the impinging radiation
Thermal detectors
87
Thermal detectors are used for _____ because ____
infrared spectroscopy photons in IR lack the energy to cause photoemission of electrons
88
Types of thermal detectors (4)
Thermocouples Bolometers Pyroelectric transducers Pneumatic cells
89
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
Thermocouple
90
Thermocouple has ___ response time
slow
91
Thermocouple is more common in older scanning IR instruments but ___
not well suited for FT-IR
92
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
Bolometer
93
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
Bolometer
94
bolometer is very sensitive to ____ and are predominantly used in IR between ___
thermal radiation 10 to 5000 μm
95
detect photons through the heat they generate and the subsequent voltage generated in pyroelectric materials
Pyroelectric Detector
96
Insulators with very special thermal and electrical properties
crystalline wafers (triglycine sulfate TGS) of pyroelectric materials
97
takes place when an electric field is applied across a dielectric material
electric polarization
98
Even after removal of the field, they retain a ___
temperature-dependent polarization
99
TGS crystals have ___ response time and are _____ as detectors for FT-IR
fast suitable and common
100
FT-IR Spectroscopy TGS
Fourier transform Infrared Spectroscopy Triglycine Sulfate

Analytical Chemistry (13 decks)

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