analytical II unit 5 intro to photoluminescence

Question 1

luminescenct methods (3)

Answer 1

flouresence, phosphorescene and chemiluminescence

Question 2

what happens in luminescent methods?

Answer 2

molecules are excited (absorb E) to yield a species that emits radiation and whose emission spectrum provides analytical information

Question 3

how does absorption occur in flourescence and phosporesecence?

Answer 3

excitation occurs by absorption of a photon. (radiation from a molecule that has been previously excited by photons or uv / visible radiation)

Question 4

does flourescence involve a change in electron spin?

Answer 4

no

Question 5

does phosphorescence involve a change in electron spin?

Answer 5

yes

Question 6

does flouresence or phosphorescence have a shorter lifetime?

Answer 6

flourescence has a much shorter lifetime

Question 7

what happens in chemiluminescence?

Answer 7

the emitting species is formed in the course of a chemical reaction. sometimes the analyte does not participate in the reaction

Question 8

what is resonant emission and how common is it?

Answer 8

emission of radiation at the same wavelenth that it absorbs (very rare in molecules as some energy is often dissipated as heat)

Question 9

How does phototluminescence work and how is it different to other absorption spectra?

Answer 9

when a molecule absorbs energy of a certain wavelength it reaches an excited state. It then has to return the excess energy to the system.
it can do this by 2 routes.
1) x + heat. releses this extra energy in the form of heat through colisions with other atoms and neighbouring mollecules (absoption spectroscopy)
2) x + heat + hv . emitting electromagnetic radiation (hv) that can be measured and often visibly seen (photoluminescence)

Question 10

luminesence definition

Answer 10

Emission of radiation as a consequence of the deactivation of a molecule

Question 11

photoluminescence

Answer 11

Emission of radiation as a consequence of deactivation when excitation takes place by absorption of photons

Question 12

chemiluminescnce

Answer 12

Type of luminescence in which excitation does not occur by a photon absorption process, but by a chemical reaction

Question 13

bioluminescence

Answer 13

Chemiluminescence phenomena in living organisms (fireflies)

Question 14

triboluminescence definition

Answer 14

Release of stored E in certain crystalline substances upon breakage

Question 15

florescence or photoluminescence? what does it depend on?

Answer 15

depends on the mechnism by which the activated species returns to its ground state.

Question 16

advantages of luminescent methods in comparison to traditional absorption methods

Answer 16

wider linearity ranges, significantly larger than traditional absoprtion methods
inherintly sensitive. LODs 1-3 orders of magnitude lower that absorption spectroscopy
more selective than absorption as there are not too many molecules with luminescent properties that can interfere

Question 17

molecular multiplicity equation

Answer 17

M=2S+1 (S= total spin quantum number, sum of spins of each of the electrons)

Question 18

molecular multiplicity in diamagnetic molecules

Answer 18

Singlet state (M=1). All spins are paired, no splitting of E because S=0

Question 19

molecular multiplicity in paramagnetic molecules

Answer 19

Doublet state (M=2) the odd electron can take 2 orientations in a magnetic field

Question 20

is the lifetime of an excited T state larger than an excited S state?

Answer 20

yes

Question 21

how are the elctrons arranged in a ground singlet state?

Answer 21

—————— *

–up/down—–

Question 22

how are the elctrons arranged in an excited singlet state?

Answer 22

——–down———- *

———–up———-

Question 23

how are the elctrons arranged in an excited triplet state?

Answer 23

——–up———- *

——–up———-