Vibrational spectroscopy

Question 1

What is a vibrational transition?

Answer 1

Transition between vibrational energy levels

Question 2

What is the value of r at the bottom of the well equal to?

Answer 2

Equilibrium bond distance

Question 3

What must the mode have for a specific vibrational mode to absorb or emit infared radiation?

Answer 3

The mode must have a dipole moment that changes during the period of the molecular vibration

Question 4

What type of molecules do not usually absorb/emit infared radiation?

Answer 4

Homonuclear diatomics

Question 5

What type of molecule have observable infared spectra?

Answer 5

Heteronuclear diatomics

Question 6

What are the three different ways an atom can move?

Answer 6

Rotation
Translation
Vibration

Question 7

How many different movements do diatomic atoms have?

Answer 7

3 translations
2 rotations
1 vibrations

Question 8

What do you need to make sure for the movements of diatomics?

Answer 8

That there is either a translation, rotation or vibration but not a mixture of them

Question 9

Why don’t you want a mix of movements for diatomics?

Answer 9

A mixture wont give us the simplest, more reducibly outcome in terms of describing a system

Question 10

what happens if you can change the dipole moment as a result of the vibrational moment?

Answer 10

It will absorb IR radiation

Question 11

What happens if you cant change the dipole moment as a result of the vibrational moment?

Answer 11

It wont absorb the IR radiation

Question 12

What are the 4 modes of CO2?

Answer 12

Symmetric stretch
Bending motion
Asymmetric stretch
Bending motion

Question 13

Which modes of CO2 are IR active?

Answer 13

Bending

Asymmetric

Question 14

What are the features of a symmetric vibration?

Answer 14

No dipole moment change

IR inactive

Question 15

What is the equation to work out the number of vibrational nodes in a linear molecule?

Answer 15

3N-5

N is the number of atoms

Question 16

What is the equation to workout the number of vibrational nodes for non-linear molecules?

Answer 16

3N-6

N is the number of atoms

Question 17

What do translation and rotation modes add to?

Answer 17

5

Question 18

What do vibrational modes of H2O all lead to?

Answer 18

A change in dipole moment

Question 19

What are the three modes of H2O?

Answer 19

Bending
Symmetric
Antisymmetric

Question 20

Are the H2O nodes IR active or inactive?

Answer 20

Active

Question 21

How many modes of vibration do translations have?

Answer 21

3

Question 22

How many modes of vibrations do rotations have?

Answer 22

3

Question 23

What are the 6 molecular motions?

Answer 23

Symmetrical stretching 
Antisymmetrical stretching 
Scissoring 
Rocking 
Wagging 
Twisting

Question 24

Which molecular motions are found at higher frequencies?

Answer 24

symmetric stretch

Asymmetric stretch

Question 25

What are vibronic transitions?

Answer 25

Change in the vibrational level during an electronic transition

Question 26

When is the equilibrium bond length longer?

Answer 26

In an electronically excited state

Question 27

What is the stokes shift?

Answer 27

The difference in wavelength between λmax in the fluorescence spectrum and λmax in the absorption spectrum

Question 28

what is absorption and fluorescence in the solution phase able to do?

Answer 28

Reduce in level without emitting a proton