UV/Vis Molecular Absorption Spectroscopy

Question 1

what is present in uv/vis molecular absorption

Answer 1

vibrational, rotational and electronic transitions

Question 2

what are the two absorbing species

Answer 2

1. organic

2. inorganic

Question 3

allowed molecular transitions

Answer 3

σ→σ*
π→π*
n→σ*
n→π*

Question 4

λ range for σ→σ*

Answer 4

< 180 nm (vacuum UV)

Question 5

λ range for n→σ*

Answer 5

15-250 nm

Question 6

λ range for n→π*

Answer 6

200-700 nm

Question 7

λ range for π→π*

Answer 7

170-700 nm

Question 8

ε range for n→σ*

Answer 8

100-3000

Question 9

ε range for n→π*

Answer 9

10-100

Question 10

ε range for π→π*

Answer 10

1000-15000

Question 11

molecules that contain unsaturated function group to provide π orbitals

Answer 11

chromophores

Question 12

what absorption are considered for inorganic species?

Answer 12

1. Elements of the first and second transition metal series
2. Lanthanide and actinide ions
3. Charge transfer absortion

Question 13

what does absorption involve for first and second transition metal series

Answer 13

transtiosn between filled and unfilled d-orbitals

Question 14

what does the energy difference between d-orbitals depend on

Answer 14

1. the position of the element in the periodic table
2. the oxidation state of the element
3. The nature of the ligand bonded to it

Question 15

what does a different position on the periodic table lead to for first and second transition metal series

Answer 15

a different observed λ max

Question 16

what says the energy difference between d orbitals depends on the ligands bonded to the metal ions

Answer 16

ligand crystal field theory

Question 17

what does octaheadral ligand field say for the d orbitals

Answer 17

Dx2-y2 = Dz2

Greater than

Dxy = Dxz = Dyz

Question 18

Tetraheadral ligand field

Answer 18

Dxy=Dxz+Dyz

greater than

Dx2-y2 = Dz2

Question 19

square planar ligan field

Answer 19

Dx2-y2

greater than

Dxz

greater than

Dz2

greater than

Dxy = Dyz

Question 20

what is the magnitude of ∆ relate to

Answer 20

the spectrochemical series

Question 21

what is the order of the spectrochemical series

Answer 21

CN->NO2>o-phen>EN>NH3>SCN->H2O~C2O4 2->OH->F->Cl->Br->I-

CN has highest ligand field strength while I- has the lowest ligand field strength

Question 22

In spectrochemical series, as λ decreases, ∆ ___

Answer 22

increases

Question 23

what electrons are responsible for absorption of lanthanides

Answer 23

4f electrons

Question 24

what electrons are responsible for the absorption of actinides

Answer 24

5f electrons

Question 25

what leads to the narrow absorption bands of lathanides and actinides

Answer 25

the full d orbital shields the f orbital responsible for absorption which leads to narrower bands.

Question 26

what is charge transfer absorption

Answer 26

when the product of an electron donor is bonded to an electron acceptor absorbs radiation, an electron from the donor is transferred to an orbital that is largely associated with the acceptor

(Internal redox reaction)

Question 27

what usually serves as the electron acceptor in charge transfer absorption

Answer 27

the metal

Question 28

five components of uv/vis molecular absorption spectroscopy

Answer 28

1. radiation source
2. wavelength selector
3. sample container
4. transducer
5. signal processor and readout

Question 29

radiation sources in UV/Vis

Answer 29

1. tungsten filament lamp
2. deuterium and hydrogen lamps
3. xenon arc lamps

Question 30

tungsten filament lamp range

Answer 30

VIS and Near IR

Question 31

deuterium and hydrogen lamp range

Answer 31

UV

Question 32

xenon arc lamp range

Answer 32

VIS and UV

Question 33

Are radiation sources continuum sources or linear?

Answer 33

continuum

Question 34

what are tungsten filament lamps based on

Answer 34

black body radiation

Question 35

original tungsten filament lamp

Answer 35

Mostly visible range
glass container
Ne gas
Tungsten filament(2870K)

Question 36

A tungstein-halogen lamp

Answer 36

quarts container
Newith 2
Tungsten filament (3000K)

Question 37

what was the advantage of tungsten halogen over the original tungsten lamp

Answer 37

the addition of I2 basically forms WI2 in the vapor of the lamp, and when the lamp is turned off the volatile WI2 hits the hot filament lamp and the W redeposits onto the filament and the I2 is dispersed back into the “air”

Question 38

what does the higher temperature of tungsten halogen lead to

Answer 38

• Higher intensities

- Extended range into UV