Ro-vibrational spectroscopy

Question 1

What are the issues with a low resolution IR spectrum?

Answer 1

It is not a sharp image so it is hard to make out the details

Question 2

What energy is there changes in?

Answer 2

Rotational energy

Vibrational energy

Question 3

What symbol is used for vibrational energy?

Answer 3

V

Question 4

What symbol is used for rotational energy?

Answer 4

J

Question 5

What is the dissociation energy?

Answer 5

The sum of the separations of the vibrational energy levels up to the dissociation limit

Question 6

How do the energy level separations compare?

Answer 6

Electronic level spacings > vibrational level spacings > Rotational level spacings

Question 7

What is the ground state?

Answer 7

The state of a system with the lowest possible energy

Question 8

What is the excited state?

Answer 8

Any state of a system with an energy higher than the ground state

Question 9

What does fundamental mean?

Answer 9

Transition between v=o and v=1 vibrational levels (lowest 2 energy levels)

Question 10

What does overtone mean?

Answer 10

A transition between v=0 and any vibrational level higher than v=1

Question 11

What is the hot band?

Answer 11

A transition between two levels that have v>O

Doesnt involve the ground state

Question 12

What does the spacing between lines depend on?

Answer 12

Rotational constant

Question 13

What temperature is rotational-vibrational spectra usually seen at?

Answer 13

Room temperature

Question 14

What value does the spacing between two lines have?

Answer 14

2B

Question 15

How do you work out reduced mass?

Answer 15

m1 X m2 / m1 + m2

Question 16

What equation is used to work out B (rotational constant)?

Answer 16

B = h / 8π²I

Question 17

Can transitions happen between J=0 and j=0?

Answer 17

No rules say this cant happen

Question 18

What is the equation for the moment of inertia?

Answer 18

I = μr²

Question 19

What are changes in μ equal to?

Answer 19

Changes in I and changes in B

Question 20

When is the Q-branch allowed?

Answer 20

When there is an angular momentum around the axis of a linear molecule

Question 21

What are isotopologues?

Answer 21

Molecules which differ only in their isotopic composition

Question 22

What are the three branches in the spectra?

Answer 22

Q
R
P

Question 23

What is the feature of the Q branch?

Answer 23

ΔJ = 0

Question 24

What is the feature of the R branch?

Answer 24

ΔJ = +1

eg. J=2 to J=3

Question 25

What is the feature of the P branch?

Answer 25

ΔJ = -1

eg. J=3 to J=2

Question 26

What happens when the stretching mode of a diatomic molecule is excited?

Answer 26

The average internuclear separation increases

The rotational constant decreases

Question 27

In vibronic spectra, when is energy lost?

Answer 27

Through collisions

Question 28

What do changes in vibrational energy accompany?

Answer 28

Electronic transitions

Question 29

How are spectra usually assigned?

Answer 29

using a computer programme such as PGOPHER

Question 30

What is zero-point energy?

Answer 30

The lowest physically-allowed energy the molecule can have

Where v=0, the molecule still has a residual energy of 1/2 hv

Question 31

What is the equation for the vibrational energy levels of a molecule?

Answer 31

Eᵥ = hv (u + 1/2)

Question 32

What are adjacent energy levels separated by?

Answer 32

hv

Question 33

Does molecular rotation have a zero-point energy?

Answer 33

No

Question 34

Do electronic energies have a zero-point energy?

Answer 34

Yes

Question 35

What is the bottom of the well on a morse potential energy curve equal to?

Answer 35

The equilibrium bond distance, re

Question 36

How do you calculate the zero point energy?

Answer 36

1/2 hv