Molecular Luminescence Spectroscopy

Question 1

Forms of Luminescence

Answer 1

Radio
Electro
Thermo
Tribo
Sono
Photo
Chemi
Bio

Question 2

Jablonski Diagram

Answer 2

Vibrational Relaxation
Internal Conversion
Fluorescence
Phosphorescence
Intersystem Crossing
External Crossing

Question 3

a molecule of analyte absorbs a photon and excites a species in a process called photo-excitation

Answer 3

photoluminescence

Question 4

no excitation radiation source; molecules of analyte are excited via chemical reaction to give a species whose emission spectrum provides information for quali/quanti analyses

Answer 4

chemiluminescence

Question 5

Nonradiative deactivation

Answer 5

Vibrational Relaxation
Internal Conversion
Intersystem Crossing
External Conversion

Question 6

Radiative Deactivation

Answer 6

Fluorescence
Phosphorescence

Question 7

collisions of excited state analyte molecules with other molecules lead to loss of excess vibrational energy

Answer 7

vibrational relaxation

Question 8

molecule passes to a lower energy state, vibrational energy levels of two electronic states overlap and molecules pass from one electronic state to other

Answer 8

Internal conversion

Question 9

Spin of electron is reversed leading to change from singlet to triplet state

Answer 9

Jntersystem Crossing

Question 10

Interaction and energy transfer between the excited molecules and the solvent or other molecules

Answer 10

External Conversion

Question 11

emission of a photon via a singlet to singlet transition

Answer 11

fluorescence

Question 12

emission of a photon via a triplet to singlet transition

Answer 12

Phosphorescence

Question 13

all electron spins are paired; no energy level splitting occurs when the molecule is exposed to EMF

Answer 13

singlet

Question 14

unpaired and parallel electron spins; excited state is less energetic than the corresponding state

Answer 14

Triplet

Question 15

no net magnetic field due to spin pairing; electrons are repelled by permanent magnetic fields

Answer 15

Diamagnetic

Question 16

magnetic moment and attracted to a magnetic field

Answer 16

paramagnetic

Question 17

Types of fluorescence

Answer 17

Resonance Fluorescence
Non-Resonance Fluorescence

Question 18

absorbed radiation is re-emitted without a change in frequency and wavelength

Answer 18

Resonance Fluorescence

Question 19

molecular fluorescence bands are shifted to wavelengths that are longer than the resonance line

Answer 19

non-resonance fluorescence

Question 20

Factors affecting luminescence

Answer 20

Quantum Yield
Molecular Structure
Structural rigidity
Dissolved oxygen
temperature
solvent
pH

Question 21

Quantum yield formula

Answer 21

total no. luminescing molecules/ total no. of excited molecules

Question 22

occurs when a molecule changes from higher electronic stage to an upper vibrational level of a lower electronic state in which the vibrational energy is strong enough to rupture the bond

Answer 22

Predissociation

Question 23

occurs when radiation promotes a molecule directly to a state with sufficient vibrational energy for a bond to break

Answer 23

Dissociation

Question 24

compounds that do not fluoresce have structures that ____

Answer 24

permit rapid relaxation by nonradiative processes

Question 25

what increases fluorescence intensity?

Answer 25

increasing benzene substituents, decreasing molar mass of substituents, increasing substitution in oxygenated species

Question 26

Flexibility increases, quantum yield?

Answer 26

decreases

Question 27

____ in a molecule causes an enhanced internal conversion rate and a consequent increase in likelihood for nonradiative deactivation

Answer 27

lack of rigidity

Question 28

Luminescence favored in molecules with ___ structures

Answer 28

rigid

Question 29

Presence of dissolved oxygen, ___ fluorescence

Answer 29

reduces

Question 30

Luminescence favored ____ temperatures

Answer 30

lower

Question 31

___ solvent is preferred in luminescence

Answer 31

polar

Question 32

luminescence preferred more ____ solvents

Answer 32

viscous

Question 33

Fluorescence and Phosphorescence relationship

Answer 33

inverse

Question 34

Fluorescence ____ if solvents contain heavy atom

Answer 34

decreases

Question 35

two thoriated tungsten made electrodes are placed face to face with a small gap in an airtight transparent envelope of fused silica filled with xenon gas in very high pressure

Answer 35

xenon arc lamp

Question 36

LASERS

Answer 36

Light Amplification by Stimulated Emission of Radiation

Question 37

LIF

Answer 37

Laser Induced Fluorescence

Question 38

determined by scanning the excitation monochromator in a range less than the preset wavelength of the emission monochromator

Answer 38

excitation spectrum

Question 39

excitation monochromator is adjusted at the determined lambda ex and emission spectrum is scanned

Answer 39

emission spectrum

Question 40

Usually the detector is set at ___ to the incident beam

Answer 40

90°

Question 41

PMT

Answer 41

photomultiplier tube

Question 42

CCD

Answer 42

charge-coupled devices

Question 43

Techniques in Molecular Luminescence Spectroscopy

Answer 43

Molecular fluorescence spectroscopy
Molecular phosphorescence spectroscopy
Chemiluminescence spectroscopy

Question 44

Fluorometer: Hg Lam and Interference filter

Spectrofluorometer:

Answer 44

xenon lamp and diffraction grating monochromator

Question 45

excited molecules lose their energies by collisions with other molecules of solvent

Answer 45

self-quenching

Question 46

when an emission ban overlaps woth an excitation, emitted photons excite other molecules in the ground state which results in no net emission

Answer 46

self-absorption

Question 47

sample tubes that are placed in liquid nitrogen held in a quartz Dewar flask

Answer 47

phosphoroscope

Question 48

produced when a chemical reaction yields an electronically excited species, which emits light as it returns to its ground states

Answer 48

chemiluminescence