3c - w - electronic spec

Question 1

how can we respresent electronic transitions : what can we draw

Answer 1

we can draw a jablonski energy level diagram

s0 , s1, s2, s3

where s0 is the ground electronic state .

s0 –> s1 = less energy that s0 —> s4

Question 2

between electronic transtions there areeee,, aka in the jabloski diagram,, between the different s levels there areeee

Answer 2

there are vibrational energy levels.

Question 3

finding energy difference between peaks in abs spec// electronic spec

Answer 3

convert wavelength to wavenumber : 1/wavelength

then do the larger energy - the lower energy.

Question 4

gross selection rule of electronic spec

Answer 4

there are no gross selection rules: u just move the e- to higher energy levels.

interaction with the electric field always induces a change in dipole moment!!!!

Question 5

wait so can homonuclear diatomics give an electronic spec

Answer 5

yessss!! a homonuclear diatomic can give an electronic spec: bc interaction with the EM always induces a change in the dipole moment

Question 6

what radiation is used in electronic spec

Answer 6

uv - vis region!!!!

Question 7

okay so whats the acc total eergy of the system ,,, what do we acc need to take into consideration + what do they tell us not to take into consideration

Answer 7

the energy of the electric trnasition,,,, vibrational transition and rotational transition.

we dont need to take rotational spec into consideration bc its energy is much lower than vibrational and electronic energy.

we consider them independently and then add them

Question 8

total energy of the system: Etotal =

Answer 8

E elec + we( v+1/2) - ( v+1/2)^2 wexe.

cm-1

Question 9

the vib levels get closer or further

Answer 9

vib levels get closer = think of anharmonic oscillator

Question 10

do rotational levels get closer or further

Answer 10

they get further

bc larger J = higher energy bc its squared

Question 11

wait so for the spec with v=0 and J’’ values,, what can we now write them as

Answer 11

lower electronic state = s0 = E’‘=0

higher electronic state = s1 = E’=1

Question 12

where do moelcules exist in

Answer 12

they exist in the lowest E’’ and V’’ levels

Question 13

what transitions between vibrational and electronic levels are possible

Answer 13

all transitions are possible ,, there are no sleection rules in electronic spec

think about the lymann and all those series and how ionisation energy can literally occur and how emission spec can be from any energy level and we find this using the rydberg equation.

Question 14

what is a progression

Answer 14

a set of transitions between electronic levelsss

(v’ ,, v’’) aka upper state and lower state. so the little piano type graph also have lines closer and closer together,, and theyre labelled at 0,0 1,0 2,0 3,0 4,0

where (upper state,, lower state)

Question 15

so the overall change in energy of the system issss

Answer 15

change in total energy = change in electronic spec + change in vib specc

Question 16

in anharmonic spec the vib lines are straight however this isnt correcttttt, what should they beeeeee

Answer 16

they should be curvesss

think like particle in a box but like in between the parabola lines of the full anharmonic curve.

Question 17

okay so 1 electronic level has vibrational levels,, so one electronic level corresponds tooooooo

Answer 17

one anharmonic curveeeee

with the vib levels being the lines in the morse curve (we know this already)

but the lines are curvyyyyyfor the vibrational levels.

Question 18

curve for v=0

Answer 18

a hill shape

Question 19

curve for v=1

Answer 19

2 hillssss
the same size

Question 20

curve for v=2

Answer 20

3 hills
big small big

Question 21

curve for v=3

Answer 21

4 curves
big small small big

Question 22

v=4 curves

Answer 22

5 hills
big small small small big

Question 23

okay so describe the hill trend

Answer 23

so number of hills = V+1

u always have 2 big ones,, and the rest are small.

Question 24

so for the electronic spec transition line and arrow thing and the diff vibrational levels

so u have the 1st electronic level made up of v’’ lines,,,, then a gap and then u have the 2nd electronic level,, with v’ vibrational levels. how do we draw the anharmonic curve for this whole thing

Answer 24

u have 2 electronic levels so u have 2 morse curves.

and they both have the curly lines for the vibrational levels.

one morse curve for v’’ (lower energy) and one morse curve for v’ (upper energy)

Question 25

why do we use curves and hills for the vibrational energy levels + what does this represent

Answer 25

bc we use |Y|^2 ,,, aka the probability distribution.

which shows us that molecules normally spend more time at the 2 extremes of the stretching and vibrating energy levels.

which makes sense bc when we have a pendulum the ball doessss spend more time at the 2 extremes.

Question 26

okay wait so higher and lower energies in the morse spec correspond to which mechanics

Answer 26

higher vib states = classical mechanics followed

lower vib levels = quantum mechanics followed.

Question 27

do molecules move during a transition

Answer 27

nopeeeee

Question 28

explain what happens when a molecule absorbs energy

Answer 28

the transition occurs
and then the molecule changes shape.

the molecule needs to make up for the change that occurs when it absorbs radiation.

so the moelcule isnt changing when it absorbs EMR.

Question 29

excited and ground states sometimes haveeeeee (think of 2 different morse curves that correspond to 2 different electronic levels)

Answer 29

they sometimes have the correct geometries.

meaning they are both alligned with the req 9aka the equilibrium bond length)

Question 30

when we have 2 morse curves aligned perfectly with identical geometries,, what do we want and when do we get it

Answer 30

the v’‘0 –> v’0 gives good and intense overlap,, bc ur going from vo to vo and both of these just have a hill as their probaility distribution.

and bc ur going from the centre of one hill to the other,, u have a high probs density at both levels.

so u get the most intense peak in vib specccc.

bc u had a good overlap of both curves,, bc their probs distributed was high in both of them!! so it adds up to to give an intense peak in vib spec.

Question 31

lower morse curve =

Answer 31

E’’ = E0 = S0

Question 32

the higher morse curve =

Answer 32

E’ = E1 = S1

Question 33

if the ground and excited states are aligned with identical geometries,, will each transition between them have high intensity

Answer 33

nopeeeee
some transitions are less likely to occur bc the overlap isnt that good between probaility distributions!!

aka if ur going from v’‘0 (the one hill) to v’1 (2 hills) ur going from the peak of one of the hills to the trough//valley of the 2 hills. so the probaility distribution is lower for the excited state.

Question 34

so u have (upper, lower) and so u get the taller lines // more intense peaks whennnnn

Answer 34

when the geometries are identicalllll!!!!!!!!

when u get the best overlap between between the probaility distribution of the ground and excited states. (the vib waves)

Question 35

what is the franck condon principle explaining

Answer 35

when theres no change in nuclear separation occuring during electronic transitions

bc they occur more rapidly compared to vibrational frequencies.

aka electronic transitions occur so rapidly in comparison to vibrational frequencies so that no change in nuclear separation occurs during the electronic transition. : the molecule changes after the transition to make up for changes made.

Question 36

OHHHHHH wait so no change in nuclear sep =

Answer 36

no change in bond length

and aka the molecule desnt move when a transition occurs.

and molecules are more likey to have a transition when the excited and ground states have the same geometries : aka the same bond lengths.

aka the morse curves look exactly the same

Question 37

classic theory dictates what vib level

Answer 37

classical dictates high vib levels

Question 38

quantume theory dictatessss

Answer 38

low vib levelssss

Question 39

wait so what do the graphs look like when they dont have identical geometries

Answer 39

one is more shifted to the right,, the higher energy one is normally shifted.

Question 40

what transitions are more likey to occur when the geometries are NOT identical

Answer 40

u just draw a line up from the v’‘0 to upper energy levels.

and whichever one has the best overlap is the best,, most intense peak!!! sometimes its the v’3,, or v’4 etcccc. just depends how much the higher morse curve is shifted.

Question 41

transitions occur predominantly from which ground states

Answer 41

they occur predominantly from the vibrational and electronic ground states.

Question 42

probability distribution of the internuclear separation is dependednt on what

Answer 42

the vibrational level.

bc u get v+1 hills.
and the intensity of the hills correspond to goof or bad overlap

and this gives us an intense transition if theyre both tall hills.

Question 43

what dictates vertical transitions

Answer 43

the frank condon principle dictates vertical transitions!!!!

Question 44

Deq

Answer 44

dissasociation equilibrium energy

Question 45

Do

Answer 45

this is the enerrgy gap between the lowest vibrational level and the plateau of the morse curve.

Question 46

what is ZPE

Answer 46

zero point energy
all molecules in ground state have vibrational energy!!

this is bc v=0 there is still vibrational energy associated with it.

Question 47

Deq =

Answer 47

Do + ZPE

Question 48

Do =

Answer 48

Deq - (1/2 we - 1/4 we xe)

Question 49

what is the continuum limit

Answer 49

the energy of the transition is more than the molecule dissociating in the excited state,, so u get a broad peak.

u get lines and then u get a line that kinda gives a broad peak type thing where the continuum limit isssss.

AKAAAAA ur going from V’‘0 —–»> draw ur line up but u dont hit a a curve for probaility distribution of vibrational levels. u just hit the edge of the morse curve and the place u hit is above the plateau.

Question 50

Do’’

Answer 50

ground state

v’‘0 —> plateau’’

Question 51

Do’

Answer 51

excited state

v’0 —> plateau’

Question 52

what happens if a molecule is super unstable

Answer 52

u dont even get a morse curve

u just get a slope type beat

Question 53

whats Eex

Answer 53

from plateau’’ –> plateau’

Question 54

Vcl =

Answer 54

Eex + Do’’

Question 55

Do’ =

Answer 55

Vcl - V(0,0)

where v(0,0) is the vo’’ –> vo’ line

Question 56

when the molecule is so unstable it doesnt have a curve,, where is Eex

Answer 56

from plateau’’ to where the line ends (aka the bottom of the line when the line has a negative gradient)

Question 57

okay so if Ev = we(v+1/2) - we(v+1/2)^2 xe what is change in energy at dissociation level

Answer 57

change in E = Ev+1 - Ev = 0

change in E =
we(1-2 xe ( vmax +1)) = 0
bc the lines are so close together

Question 58

vmax equation

Answer 58

= (1/2xe) - 1

Question 59

what is vmax

Answer 59

the max vibrational level aka where the morse curve plateausssssssss!!!

Question 60

finding v max tells us what

Answer 60

the energy at dissociation

u can find thid by finding xe. and putting it into the change E = we(1-2 xe ( vmax +1)) = 0

which finds the energy at dissociation level.