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Instrumental Analysis > Quiz 1 > Flashcards

Quiz 1 Flashcards

1
Q

Define spectroscopy.

A

interactions of radiation and matter

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2
Q

what are photons

A

discrete particles of energy

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3
Q

What is the QM description of EM radiation

A

permanent transfer of energy as stream of photons

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4
Q

electron volts

A

kinetic energy gained from one electron accelerating from rest

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5
Q

radiation source

A

generates beam with enough power to detect

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6
Q

wavelength selector

A

isolates region of spectrum to analyze

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7
Q

sample holder

A

transparent container

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8
Q

radiation detector

A

converts energy to usable electrical signal

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9
Q

signal processor

A

displays results

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10
Q

what is a continuous source?

A

changes in intensity slowly as a function of wavelength

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11
Q

What is a discontinuous source?

A

limited number of bonds, limited range

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12
Q

What is the luminescence of a black-body source?

A

flux of radiation escaping from small hole

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13
Q

What is the Wien Displacement Law?

A

increasing temperature increases emitted I, wavelength max to shorter wavelength

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14
Q

What is the spectral emissivity of a black-body source?

A

ratio of spectral radiance of a source to that of a black body radiator; varies between 0 and 1 with 1 being exactly black body

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15
Q

What is a gray body source?

A

real sources, emissivity less than 1

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16
Q

gas discharge continuous source

A

low pressure, UV, D + H lamps, 160 - 380 nm

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17
Q

In what types of spectroscopies are discontinuous sources commonly used?

A

atomic, fluorescent, raman

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18
Q

What are the requirements for discontinuous sources?

A

sufficient radiant power in relevant wavelengths, stable and constant intensity

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19
Q

How are discontinuous sources
stabilized?

A

regulated power, 2 beam instrument

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20
Q

What are the various types of discontinuous sources?

A

metal vapor lamp, electrodeless discharge, hollow cathode

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21
Q

Where are dispersive methods commonly used

A

UV/VIS/NIR and Raman; manufactor of lenses

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22
Q

where are non-dispersive methods commonly used

A

Infrared and NIR, increasing in Raman and MS

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23
Q

Dispersive elements

A

filter, prism, grating

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24
Q

interference filters rely on

A

optical interference to provide narrow band

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25
Q

absorbance filters

A

absorbs selected portions of spectrum

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26
Q

What is the physical principle behind interference filters?

A

optical interference

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27
Q

How are interference filters constructed?

A

thin, transparent dielectric material sandwiched between 2 thin semitransparent metal films

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28
Q

What controls the wavelengths of transmitted light through an interference filter?

A

constructive interference

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29
Q

What is the physical principle behind absorbance filters?

A

absorption of radiation by colored glass, crystals, dyes, solutions, etc. that allow radiation to be transmitted only in certain regions

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30
Q

What is a bandpass filter?

A

allows a certain region of radiation to be transmitted

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31
Q

What is a cut-off filter?

A

cuts off everything below or above a certain wavelength and passes all of the rest of the radiation

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32
Q

Absorbance filters governed by

A

wavelength, transmission and bandwidth

33
Q

What is the physical principle behind the use of prisms as dispersive devices?

A

light from low to high refractive toward normal, high to low bends away

34
Q

How does light reflect in prisms?

A

light enters toward normal and exits away

35
Q

Which wavelength (red or blue) is
more highly refracted in a prism? Why?

A

blue because its shorter

36
Q

angular dispersion units

A

rad nm-1

37
Q

linear dispersion units

A

mm nm-1 or mmA-1

38
Q

What is the reciprocal linear dispersion?

A

the figure of merit for comparing the dispersion properties of optical elements

39
Q

why is reciprocal linear dispersion useful

A

lower D-1 is better

40
Q

What is a reasonable magnitude for resolving power in prisms?

A

9%

41
Q

What is the Rayleigh Criterion?

A

use to see if two adjacent are fully resolved

42
Q

What is a grating?

A

disperses radiation into component wavelengths

43
Q

What is the physical principle behind the use of gratings as dispersive devices?

A

dispersion is a result of diffraction at reflective surface

44
Q

What is the angular dispersion of a grating?

A

dr/dλ

45
Q

What is the resolving power of a grating?

A

limit of ability to separate adjacent images with similar wavelengths

46
Q

What is a reasonable magnitude for resolving power in gratings?

A

10^3 to 10^4

47
Q

What is a blazed grating?

A

concentrates large percent of diffracted into certain place

48
Q

What is the blaze angle?

A

groved for broad reflective face and unused narrow

49
Q

What is the blaze wavelength?

A

first order wavelength corresponding to m=1 diffracted

50
Q

What are the 2 processes for producing diffraction gratings?

A

holographic and mechanical

51
Q

advantages holographic

A

perfect grooves, no ghosts

52
Q

advantages mechanical

A

accurate and efficient

53
Q

disadvantages mechanical

A

hard to make

54
Q

What are some common groove densities in gratings?

A

UV: 1800 or 2400
VIS: 1200
IR: 600 or 300

55
Q

What are the components of a Czerny-Turner monochromator?

A

concave mirrors, reflection grating, focal plane

56
Q

What are the components of a general monochromator?

A

entrance slit, collimating lense, grating, focusing, exit slit

57
Q

What is monochromator dispersion?

A

influences ability to separate wavelengths

58
Q

What is the effective bandwidth of a grating monochromator?

A

1/2 width wavelength distribution passed by slit

59
Q

What is the resolving power of a monochromator?

A

ability to separate adjacent lines

60
Q

How are different wavelengths passed through the exit slit of a monochromator?

A

rotating dispersive element

61
Q

What is the take-off angle? φ

A

angle diffracted ray makes with optical axis (the light path)

62
Q

What is the grating rotation angle? θ

A

angle grating makes with optical axis (light path)

63
Q

How are take off and grating rotation angles related to the angles of incidence and diffraction from the grating?

A

α = incidence
β = diffraction
θ = α + φ
φ = θ - β
α = θ - φ
β = θ + φ

64
Q

What is the slit function of a monochromator?

A

triangular function where entrance and exit images overlap

65
Q

How does the shape of the entrance and exit slits determine the instrumental spectral profile?

A

diffracted radiation from grating and collimating mirror produces image of entrance in focal plan of exit. slits must be same width for triangular shape.

66
Q

propagation

A

how it moves through a medium

67
Q

arc lamps continuous source

A

high temp, very intense source with good UV output. molecular fluorescence

68
Q

filament lamps continuous source

A

glowing incandescent filaments, visible absorption. UV Vis and near IR

69
Q

glowing inert solids continuous source

A

IR/Far IR range

70
Q

gas discharge wavelengths

A

160 to 380

71
Q

arc lamps wavelengths

A

250 to 600

72
Q

filament lamp wavelengths

A

240-2500, 350-2200

73
Q

glowing inert solid wavelengths

A

1200 to 40,000; 400-20,000

74
Q

pros of prisms as dispersive devices

A

cheap, easy to make, adjustable, no overlap

75
Q

cons of prisms

A

low dispersion, resolving power, light flux; no far-Ir or far-Uv, nonlinear wavelength

76
Q

holographic production of gratings

A

coat flat glass with photosensitive material, laser projects pattern, photosensitive layer notes groove placement to be etched, metal coat to reflect

77
Q

mechanical production of gratings

A

diamond grooves flat glass that is then covered with reflective metal via vapors. master made first, resin cast made, metal coat new form

78
Q

pros of gratings

A

efficient for wavelength separation, no limiting optical, very wide spectral range, constant linear dispersion, size and shape varied to change results

79
Q

cons of gratings

A

overlap, confusing resolution

Instrumental Analysis (45 decks)

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