Spectroscopic Methods

Question 1

Absorption

Answer 1

Methods that are based upon attenuation ( or weakening) of a beam of light when it interacts with an analyte

Question 2

Emission

Answer 2

Methods that are based upon the light given off after an analyte has been excited by thermal, electrical, or radiant energy

Question 3

Methods based on the adsorption of radiation

Answer 3

UV-VIS, IR, Raman, Microwave, NMR, mass spec

Question 4

Methods based on emission of radiation

Answer 4

Atomic spec, fluorimetry,

Question 5

UV-VIS

Answer 5

Measures adsorption of ultraviolet and visible light in a species

Question 6

Transmittance

Answer 6

The fraction of incident radiation transmitted by the sample

T = I/Io

Question 7

Absorbance (A)

Answer 7

Quantity defined by A = £bc, where £ is the molar absorptivity, b is the length of the measuring cell, and c is the concentration

Question 8

Beer-Lambert Law

Answer 8

A = -logT = 2 - log(%T) = £bc

Question 9

IR spectroscopy

Answer 9

Spectroscopic technique that analyzes the vibrations of a molecule due to the adsorption of IR radiation

Question 10

Modes of vibration

Answer 10

The band shapes and positions depend on the symmetry of the molecule’s vibrations

Question 11

Modes of vibration

Answer 11

Symmetric stretch, asymmetric stretch, twist, wag, bending, rocking, scissoring

Question 12

IR

Answer 12

The higher the bond order the higher the IR frequency

The greater the mass difference of the atoms involved in the vibrating bond the greater the frequency

Question 13

Group frequencies

Answer 13

Are associated with specific groups of atoms producing IR bands that are composite modes of vibration. Several of these groups consist of organic functional groups

Question 14

Raman spectroscopy

Answer 14

Complements IR, measures the difference in the frequencies of the scattered light after it hits a compound resulting in emergent light that contains frequencies that differ from the original one, used for identification purposes

Question 15

Microwave spectroscopy

Answer 15

Analyzes the absorption of light in the microwave region which results in changes in the rotational frequency levels of gaseous polar molecules. Used for structural information

Question 16

NMR

Answer 16

Measures the chemical shift of the protons or atoms in order to identify the compound

Question 17

Resonance

Answer 17

The energy gap corresponds to the radio-frequency range, and radiation in that range can excite the nuclei, inducing spin flips between the higher and lower energy states

Question 18

Upfield

Answer 18

Signals of more shielded protons, to the right

Question 19

Downfield

Answer 19

The signals of less shielded protons, to the left

Question 20

Spin-spin splitting

Answer 20

Indicative of the magnetic nonequivalence of protons located on adjacent carbon atoms. N+ 1 peaks are observed in the slitting of a given proton signal of N magnetically equivalent protons are found in the adjacent carbon

Question 21

Atomic spectroscopy

Answer 21

Based on the emission of radiati n after the adsorption of energy by a sample, usually used for elemental trace analysis

Question 22

Atomization

Answer 22

The sample is volatilizations and decomposed to produce particles, which can either be atoms or ions

Question 23

Fluorescence

Answer 23

Caused by the absorption of radiant energy and reemission of some of this energy in the form of light, light emitted is almost always a high wavelength then the light absorbed

Question 24

Phosphorescence

Answer 24

The phenomenon that occurs when an interstate crossing occurs to a state of different multiplicity, the light is emitted with a time delay

Question 25

Total fluorescence intensity

Answer 25

F = Io • 2.3£cl(omega)

Io = intensity of the incident light
l = cell length
Omega = quantum yield of fluorescence