Johnston

Question 1

Spectroscopy involves interaction of ________________

Answer 1

Light with matter

Question 2

Explain absorption in terms of electron transitions

Answer 2

Light with an energy hv excites the electron from the ground state (ψ’’) to a quantised energy level known as the excited state (ψ’)

Question 3

What is the fine structure of an electronic structure?

Answer 3

Electronic is broken down into Vibrational

Vibrational is broken down into Rotational

Question 4

What is the energy change of the electronic fine structure?

Answer 4

2x10^4 - 10^5 cm^-1
wavelength is approximately 500-100nm
UV - Vis

Question 5

What is the energy change of the vibrational fine structure?

Answer 5

10^2 - 5x10^3 cm^-1
Wavelength is approximately 100μm -2μm
Infrared region

Question 6

What is the energy change of the rotational fine structure?

Answer 6

3-300 GHz
Wavelength is approximately 10-1mm
Microwave region

Question 7

Equation linking velocity of light in vacuum (c) with wavelength and frequency

Answer 7

c = νλ

Question 8

Equation of wavenumber

Answer 8

ν ˜=ν/c = 1 / λ

Question 9

What is the mass of an electron?

Answer 9

0.910953x10-30 kg

Question 10

What is planks constant?

Answer 10

6.626x10-34 J s

Question 11

What is the Boltzmann constant?

Answer 11

1.390x20-23J K-1

Question 12

What does the hat mean above a letter “^”?

Answer 12

Operator

Question 13

What is the basic format of the Schoringer equation?

Answer 13

Ĥψ(x)=Eψ(x)

Question 14

Explain the Born Oppenheimer approximation and when would this approximation be used?

Answer 14

Electrons are much lighter than the nucleus and therefore move much faster. This leads to the assumption that the nucleus is stationary and the electrons move around the nucleus in electronic spectroscopy. This does not stand true for vibrational spectroscopy

Question 15

Why is the fine structure for translational symmetry not observed?

Answer 15

They are so close in energy the levels turn into a continuum therefore there’s no distinct transitions

Question 16

What is the name of the simplest MO theory

Answer 16

Linear Combination of Atomic Orbitals

Question 17

Explain the outcome when you produce two molecular orbitals from atomic orbitals

Answer 17

A bonding and an anti bonding molecular orbital is formed. The bonding orbital will be lower in energy than the anti bonding orbital with the descriptor ψ+ where ψ+= CAφA + CBφB (where A and B are subscripts).

The anti bonding orbital will be higher in energy than the bonding orbital and the atomic orbitals with a descriptor ψ-= CAφA - CBφB (where A and B are subscripts).

Question 18

How do you label MO’s?

Answer 18

g = symmetrical 
u = anti-symmetrical 

σ = 0 Nodes (analogous of s) 
π = 1 Node (analogous of p) 
δ = 2 Nodes (analogous of d)

Question 19

What is the difference between the bonding and anti-bonding orbitals?

Answer 19

Bonding orbitals:
If R is large there is a large nuclear separation leaving the 2 independent AO’s. Smaller R leads to constructive interference between one another. σg
ψ+ = N+(φA + φB)
Anti-bonding orbitals:
If R is large there is a large nuclear separation leaving the 2 independent AO’s. Smaller R leads to destructive interference between one another. σu*

ψ- = N-(φA - φB)

Question 20

What is observed on a MO diagram when there is a small 2s-2p energy gap?

Answer 20

E(3θg) > E (1πu)

Question 21

What are the 4 required symbols to find when calculating the term symbols of a diatomic molecule?

Answer 21

Orbital angular momentum Λ
Spin angular momentum (S) and thus Spin multiplicity = 2S+1
Total Electronic Angular Momentum Ω
Overall symmetry (gg=uu=g vs gu=ug=u)

Question 22

What are Hunds rules when calculating the ground state term symbol?

Answer 22

1) Maximum multiplicity
2) Max S, Min Λ
3) >1/2 filled = max Ω
<1/2 filled = min Ω

Question 23

What happens to the energy of molecular orbitals when there is small 2s-2p mixing?

Answer 23

mixing and E(5θ) > E (1π)

Question 24

What happens to the energy of molecular orbitals when there is large 2s-2p mixing?

Answer 24

mixing and E (1π) > E(5θ)

Question 25

What is the Pauli Exclusion Principle?

Answer 25

No 2 electrons can have the same 4 quantum numbers

Question 26

For heteronuclear diatomics of A2 symmetry, what point group is applied? What affect does this have on the term symbol?

Answer 26

C∞v The two π electrons will have π symmetry as such: πxπ = ∑+ + [∑-] + Δ where [] shows the triplet term

Question 27

For homonuclear diatomics of A2 symmetry, what point group is applied? What affect does this have on the term symbol?

Answer 27

D∞h Electron in πg/πu* has πg/πu symmetry as such πxπ = ∑+ + [∑-] + Δ all combinations of S and Λ are allowed

Question 28

When writing the electronic configuration of a diatomic molecule, how does the makeup of the molecule affect the numbers within the configuration? eg 1,1,2,2,3,3 vs 1,2,3,4,5,6

Answer 28

staggered if the diatomic is the same atom eg O2 eg 11,22,33,44 continuous if diatomic is different eg CO

Question 29

Energy of orbitals for a large atomic gap (hormo and hetero)

Answer 29

HOMONUCLEAR 1θ <1π. EG O2, F2 | HETERNUCLEAR 5θ >1π. EG CO

Question 30

Energy of orbitals for a small atomic gap (homo and hetero)

Answer 30

HOMONUCLEAR 1π < 1θ. EG C2, B2 | HETERNUCLEAR 1π > 5θ. EG NF

Question 31

How do you calculate intermolecular separation from ωe and Be?

Answer 31

``` Be = h/8π^2 I*c I = μRe^2 ```

Question 32

Describe Valence excited states

Answer 32

The excitation of an electron within the degenerate set of MO's

Question 33

When a molecule is excited, how is Re (eqbm bond length) and ωe (vib wavenumber) effected?

Answer 33

Stays pretty constant constant

Question 34

What is the Rydberg excited state?

Answer 34

An atom/molecule that is electronically excited with energy following the Rydbergg

Question 35

What is the Rydberg formula?

Answer 35

E(n) = -R/(n-d1)2 Where R = Rydberg constant n = Principle quantum number d1 = quantum defect

Question 36

What are the selection rules for molecular excitation?

Answer 36

1) Orbital Angular Momentum ΔΛ = 0 or +/- 1 2) Spin: ΔS = 0 3) Total angular momentum: ΔΩ = 0, +/- 1 4) Laporte (g/u symmetry): u g 5) symmetry -> ∑+ --> ∑+ and ∑- --> ∑-

Question 37

Intensity of an electronic transition moment:

Answer 37

Proportional to the Rel^2

Question 38

Why must ΔS = 0 ?

Answer 38

A photon does not contain any spin and therefore results in no change in the total spin

Question 39

What is the Beer-Lambert law?

Answer 39

Absorbance = ε.C.L where ε is the molar absorption coefficient, C is concentration and L = length of sample

Question 40

Why are forbidden transitions seen?

Answer 40

spin orbit coupling

Question 41

What is the term symbol for a closed shell?

Answer 41

1∑g where S=0 ALWAYS

Question 42

What is the rules for applying +/- with the term symbols for ∑ values

Answer 42

Completely filled orbital = + Partially filled θ orbital = + Partially filled π orbital = -

Question 43

What is the potential energy of a harmonic oscillator?

Answer 43

V(x) = 1/2 k x^2 where x = R-Re

Question 44

How do you calculate the harmonic wavenumber?

Answer 44

ωe = (1/2πc)*(sqrt(k/μ)

Question 45

How do you calculate the harmonic frequency?

Answer 45

v = 1/2π*(sqrt(k/μ)

Question 46

What is the Franck Condon Principle?

Answer 46

The relative absorption and emission intensities of v' and v'' peaks are partially dependant on the degree of overlap of the wave function. Where I(v',v'') = [integral Ψ'v(v')*Ψ''(v") dt]^2 When v'max = large, band width is broad when v' max = small, band width is narrow

Question 47

Describe a band head and determine the two types?

Answer 47

an abrupt edge of a rotational spectroscopic band in a molecular electronic spectrum. A band head is observed when dṽ/dJ = 0 1) Red-degraded band head 2) Blue-degraded band head

Question 48

Explain red-degraded band heads

Answer 48

Arise from Re'>Re'' and thus B'λBH = no rotational structure λ< λBH = intensity of the rotational lines decay Causes BOND WEAKENING J head = (3B' - B'')/2(B" - B')

Question 49

Explain blue-degraded band heads

Answer 49

Arise from Re'>Re'' and thus B'>B" (ΔB > 0) P BRANCH λ λBH = intensity of the rotational lines decay Causes BOND STRENGTHENING Jhead = (B' + B")/2(B'-B")

Question 50

Explain bond weakening transitioning

Answer 50

R Branch: J head = (3B' - B'')/2(B" - B') P Branch: ṽ[P(J)] = ṽ(v'v") - J(B' + B") + J^2 (B' - B") (no change in direction) Q Branch: Overlaps its P branch

Question 51

Explain bond strengthening transitioning

Answer 51

Blue degraded P branch: Jhead = (B' + B")/2(B'-B") R Branch: ṽ[R(J)] = ṽ(v'v" + 2B') - J(3B' + B") + J^2 (B' - B") Q Branch: Overlaps its P branch