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Instrumental and Analytical Chemistry > Spectroscopy > Flashcards

Spectroscopy Flashcards

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1
Q

study of the interaction of electromagnetic radiation with matter. It explains how materials absorb, transmit or emit radiation

A

spectroscopy

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2
Q

give qualitative and quantitative information about the system studied

A

spectroscopic methods

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3
Q

form of energy that travels through space at an extremely high velocity

A

electromagnetic radiation

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4
Q

in electromagnetic fields, the waves consist of ________ electric and magnetic fields

A

perpendicularly oscillating

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5
Q

fails to account for phenomena associated with the absorption and emission of radiant energy. For these processes, electromagnetic radiation can be treated as discrete packets of energy or particles called photons or quanta

A

the wave model

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6
Q

linear distance between sucessive maxima or minima of a wave

A

wavelength

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7
Q

is a vector quantity that provides a measure of the electric or magnetic field strength at a maximum in the wave

A

amplitude (of an electromagnetic wave)

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8
Q

the number of oscillations that occur in one second

A

frequency

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9
Q

unit of frequency of an EMR

A

Hertz

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10
Q

the frequency of a beam of EMR does not ____ as it passes through different media

A

change

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11
Q

the number of waves per centimeter and is equal to 1/wavelength

A

wavenumber

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12
Q

In a vacuum, light travels at its ____ velocity and this velocity is giving the special symbol c

A

maximum

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13
Q

Speed of light in a vacuum

A

2.99792 x 10^8

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14
Q

Speed of light formula

A

Frequency x wavelength

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15
Q

in a medium containing matter, light travels at a veocity ________ C because of interaction between the electromagnetic field and electrons in the atoms or molecules of the medium. Radiation velocity and wavelength both decrease as the radiation passes from a vacuum or from air to a denser medium. Frequency remains constant

A

less than

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16
Q

a particle of electromagnetic radiation having zero mass and an energy of hV.

A

photon

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17
Q

photon energy equation

A

Planck’s constant x velocity of light in a vacuum x wavenumber

E = hcν

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18
Q

Planck’s constant

A

6.63x10^-34 Js

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19
Q

types of interaction of electromagnetic radiation with matter

A
  • absorption
  • emission
  • reflection
  • scattering
  • diffraction
  • interference
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20
Q

process where a molecule absorbs EMR that excites electrons. This absorption of energy causes an electronic transition from a groung state (non-excited) to an excited state

A

absorption

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21
Q

transition from a higher to lower state which releases EMR from the atom or molecule

A

emission

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22
Q

electronic transitions involving pi, sigma and non bonded electrons

A

organic molecules

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23
Q

electronic transitions involving d and f electrons

A

inorganic compounfs

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24
Q

electronic transitions involving change transfer electrons

A

inorganic compounds

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25
Q

Uses ultraviolet and visible radiation.
Absorbed EMR induces electronic transitions (absorption peaks)
Identifies functional groups
Access to molecular structure and oxidation state

A

UV-visible spectroscopy

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26
Q

Pros of UV visible spectroscopy

A
  • economic
  • non-invasive (fibre optics allowed)
  • versatile (solid, liquid gas)
  • extremely sensitive (concentration
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27
Q

Cons of UV-visible spectroscopy

A
  • No atomic resolution
  • Broad signals (resolution)
  • Time resolution (S/N)
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28
Q

An electron in a bonding s orbital is excited to the corresponding antibonding orbital. The energy required is large. For example, methane shows an absorbance maximum at 125nm (which has only C-H bonds and can only undergo transitions of this type). Absorption maxima due to these transmitions not being seen in typical UV-VIS spectra (200-700 nm)

A

σ → σ*

Electronc transitions in organic molecules

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29
Q

Absorption of radiation by ________ in the wavelength region between 180 and 780 results from interactions between photons and electrons that either participate directly in bond formation or that are localised about such atoms as oxygen, sulphur, nitrogen and the halogens

A

organic molecules

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30
Q

consists of an electron donor group bonded to an electron acceptor

A

charge-transfer complex

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31
Q

when a ____ absorbs radiation, an electron from the donor is transferred to an orbital that is largely associated with the acceptor. The excited state is thus the product of a kind of internal oxidation/reduction process

A

charge-transfer complex

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32
Q

radiant power in watts incident on sample

A

incident radiant power P0 (incident intensity)

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33
Q

radiant power transmitted by sample

A

transmitted radiant power P

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34
Q

Log (incident radiant power/transmitted radiant power)

Log(P0/P) or Log T

A

Absorbance A

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35
Q

transmitted radiant poiwer/incident radiant power

P/P0

A

Transmittance T

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36
Q

Length over which attenuation occurs

A

path length of sample, b

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37
Q

As light traverses a medium containing an absorbing analyte, the intensity ____ as the analyte becomes excited

A

decreases

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38
Q

As light traverses a medium containing an absorbing analyte, the intensity ____ as the analyte becomes excited

A

decreases

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39
Q

Absorbance is directly proportional to the concentration of the absorbing species c, to the path length b of the absorbing medium and a is a proportionality constant called absorptivity

A = Log (P0/P) =abc

A

Beer’s Law

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40
Q

Absorbance is directly proportional to the concentration of the absorbing species c, to the path length b of the absorbing medium and a is a proportionality constant called absorptivity

A = Log (P0/P) =abc

A

Beer’s Law

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41
Q

equal to the sum of the absorbances of the individual components in the solution

A

total absorbances

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42
Q

Limitations of Beer-Lambert’s Law

A
  • Real deviations
  • Chemical deviations
  • Instrumental deviations
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43
Q

These are fundamental deviations due to the limitations of the law itself

Beer-Lambert’s Law

A

Real deviations

Beer-Lambert’s Law

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44
Q

These are deviations observed due to specific chemical species of the sample which is being analysed

Beer-Lambert’s Law

A

Chemical deviations

Beer-Lambert’s Law

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45
Q

These are deviations which occur due to how the absorbance measurements are made

Beer-Lambert’s Law

A

Instrumental deviations

Beer-Lambert’s Law

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46
Q

Concentration effects of Beer-Lambert’s Law

A

A higher concentrations, the individual particles of the analyte no longer behave independently of one another. The resulting interaction between particles of analyte may change the value of Ɛ

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47
Q

Beer’s law strictly applies only when measurements are made with ___________

A

monochromatic source radiation

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48
Q

If the cells holding the analyte and blank solutions are not of equal path length and equivalent in optical characteristics, an intercept will occur in the calibration curve and the equation will be

A

A = Ɛbc +k

49
Q

why we need a reference or standard measurement

A

To compensate for reflection and scattering which causes attenuation of the beam. The analyte solution is compared with an identical cell containing only the solvent or a reagent blank

50
Q

the attenuation of the course radiation at the selected wavelength is measured

A

absorption measurements

51
Q

the source excites the analyte and causes the emission of characteristic radiation, which is usually measured perpendicular to the incident source beam

A

fluorescence measurements

52
Q

To be suitable for spectroscopic studies, a source must generate a beam of radiation that is ________ for easy detection and measurement

A

sufficiently powerful

53
Q

To be suitable for spectroscopic studies, a source must generate a beam of radiation that is ____ for a reasonable period of time

A

stable

54
Q

used to isolate the desired wave so that only the band of interest is detected and measured

A

monochromator/ filter

55
Q

operate by blocking or absorbing all but a restricted band of radiation

A

filters

56
Q

optical filter that reflects one or more spectral bands or lines and transmits others, while maintaining a nearly zero coefficient of absorption for all wavelengths of interest.

Wikipedia

A

Interference filter

https://en.wikipedia.org/wiki/Interference_filter

57
Q

This type of silter usually consists of a coloured glass plate that absorbs part of the incident ration and transmits the desired band of wavelengths

A

absorption filter

58
Q

device that identifies, records, or indicates a change in one of the variables in its environment such as pressure, temperature or electromagnetic radiation

A

Detector

59
Q

Converts non-electrical quantities such as light intensity, pH, mass and temperature into electrical signals that can be subsequently amplified, manipulated, and finally converted into numbers proprtional to the magnitute of the original quantity

A

Transducer

detector

60
Q

The electrical response of the detector =

A

proportionality constant * radiant power of the beam
G = KP

61
Q

Measures the sensitivity of the detector

A

proportionality constant

62
Q

Photon detector which is based on the interaction of radiation with a reactive surface to produce electrons

A

photoemission

63
Q

Photon detector which is based on the interaction of radiation with a reactive surface to promote electrions to energy states in which they can conduct electricity

A

photoconduction

64
Q

consists of a tiny blackened surface that absorbs infrared radiation and increases in temperature as a result. The temperature rise is converted to an electrical signal that is amplified and measured

A

thermal detector

65
Q

the number of photoelectrons ejected from the photocathode per unit time is ________ proportional to the radiant power of the beam striking the surface

A

directly

66
Q

In a detector, when a voltage is applied across the electrodes, the emitted ________ are attracted to the positively charged wire anode. These electrons produce a photocurrent in the circuit.

A

photoelectrons

67
Q

In a detector, when a voltage is applied across the electrodes, the emitted photoelectrons are attracted to the positively charged wire anode. These electrons produce a ________ in the circuit.

A

photocurrent

68
Q

voltage =

A

current * resistance

69
Q

sample containers which must have windows that are transparent in the spectral region of interest

A

cells/curvettes

70
Q

absorption in the infrared region arises from _______

A

molecular vibrational transitions

71
Q

provide more specific qualitative information and are called fingerprints because no other chemical species will have an indentical one

A

IR spectra

72
Q

IR spectroscopy gives ____ data

A

qualitative

73
Q

atoms of a molecule change their relative positions without changing the position of the molecular centre of mass

A

vibration

74
Q

cannot vibrate or rotate but can move in x,y and z (translation)

A

single atom

75
Q

DOF of the vibration of a single atom

A

3

76
Q

DOF in a molecule

A

number of atoms * 3 DOF

77
Q

number of vibrations in a linear molecule

A

(3 x number of atoms) - 5

78
Q

number of vibrations in a nonlinear molecule

A

(3 x number of atoms) - 6

79
Q

number of vibrations in a solid

A

(3 x number of atoms) - 3

80
Q

Most possible vibrational modes

A
  • symmetric stretch
  • asymmetric stretch
  • wagging
  • twisting
  • scissoring
  • rocking
81
Q

Bonds containing heavier atoms vibrate more ____ than lighter ones

A

slowly

82
Q

Bonds containing ____ atoms vibrate more slowly than lighter ones

A

heavier

83
Q

stronger bonds generally vibrate ________ than weaker bonds

A

faster

84
Q

vibrational frequency =

A

1/2 pi c * √force constant/reduced mass

85
Q

reduced mass =

A

mass 1 * mass 2/ mass 1 + mass 2

86
Q

In IR spectroscopy, the ____ the atoms involved in the bond, the lower the absorption frequency, assuming a constant bond strength

A

heavier

87
Q

In IR spectroscopy, the heavier the atoms involved in the bond, the ____ the absorption frequency, assuming a constant bond strength

A

lower

88
Q

sensitive to homo-nuclear molecular bonds such as C-C and C=C

A

raman spectroscopy

89
Q

vibrational mode is associated with a change in dipole movement

A

IR active

90
Q

vibrational mode is associated with a change in polarisability and totally symmetric vibrational mode

A

Raman active

91
Q

dipole moment

Raman spectroscopy

A

changes at a vertain rate per second. If this changing dipole frequency matches a frequency in the IR electromagnetic region then absoprtion of that particular IR frequency takes place

92
Q

used for the qualitative and quantitative determination of more than 70 elements. Typically, these methods can detect parts per million to parts per billion amounts

A

atomic spectroscopic methods

93
Q

spectroscopic determination of atomic species can only be performed on a _ medium

A

gaseous

94
Q

first step in all atomic procedures, a process in which a sample is volatilised and decomposed in such a wat as to produce gas phase atoms andions

A

atomisation

95
Q

requires a light source, an atom course a monochromator to isolate the specific wavelength of light to be measured, a detector to measure the light accurately

A

atomic absorption spectroscopy

96
Q

before external energy is applied, atoms are in their _______

A

ground state

97
Q

applied energy causes atoms to be momentarily in a higher energy _______

A

excited state

98
Q

transition to or from the ground state is called a ______

A

resonance transition

99
Q

resulting spectral line from a resonance transition

A

resonance line

100
Q

In atomic absorption spectroscopy, ____ tells the element present in the sample

A

wavelength

101
Q

In atomic absorption spectroscopy, ____ gives the concentration of the element

A

intensity

102
Q

the oldest and most commonly used atomisers in atomic absorption spectroscopy

A

flame atomisers

103
Q

thermal equilibrium is ordinarily not reached in this region, and it is therefore, seldon used for flame spectroscopy

Flame structure

A

primary combustion zone

104
Q

This area is relatively narrow in stoichiometric hydrocarbon flames, is often rich in free atoms and is the most widely used part of the flame for spectroscopy

Flame structure

A

interzonal region

105
Q

In the secondary reaction zone, the products of the inner core are converted to stable molecular oxides that are then dispersed into the surroundings

A

secondary combustion zone

106
Q

it provides enhanced sensitivity because the entire sample is atomised in a short period and the average residencec time of the atoms in the optical path is a second or more

A

electrothermal atomisation

107
Q

a few microlitres of sample are deposited in the furnance by syringe or autosampler. Next, a programmed series of heating events occur: drying, ashing and atomisation

A

electrothermal atomisation

108
Q

spectroscopy which detects chemical elements which uses inductively coupled plasma to produce excited atoms and ions which emit electromagnetic radiation at wavelengths characteristic of a particular element

A

inductively coupled plasma atomic emission spectroscopy

109
Q

conducting gaseous mixture containing a significant concentration of ions and electrons

A

plasma

110
Q

type of plasma source which offers the greatest advantage in terms of sensitivity and freedom from interference

A

inductively coupled plasma

111
Q

photoluminescense process in which atoms or molecules are excited by absorption of electromagnetic radiation. The excited species then relax to the ground state, giving up their excess energy and photons

A

fluorescence

112
Q

luminescence which is longer lasting than fluorescence

A

phosphorescence

113
Q

produced when a chemical reaction yields an electronically excited molecule which emits light as it returns to the ground state

A

chemiluminescence

114
Q

chemiluminescence in a biological system

A

bioluminescence

115
Q

electromagnetic spectroscopy method which analyses fluorescence from a sample

A

molecular fluorescence spectroscopy

116
Q

diagam which illustrates the electronic states and often the vibrational levels of the molecule

A

Jablonski diagram

117
Q

produced by a transition from an excited singlet state to the ground singlet state

A

molecular fluorescence

118
Q

produced by a transition from an excited triplet state to the ground singlet state

A

molecular phosphorescence

Instrumental and Analytical Chemistry (5 decks)

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