Vibrational spectroscopy Flashcards

1
Q

What is a vibrational transition?

A

Transition between vibrational energy levels

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2
Q

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

A

Equilibrium bond distance

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3
Q

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

A

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

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4
Q

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

A

Homonuclear diatomics

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5
Q

What type of molecule have observable infared spectra?

A

Heteronuclear diatomics

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6
Q

What are the three different ways an atom can move?

A

Rotation
Translation
Vibration

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7
Q

How many different movements do diatomic atoms have?

A

3 translations
2 rotations
1 vibrations

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8
Q

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

A

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

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9
Q

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

A

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

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10
Q

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

A

It will absorb IR radiation

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11
Q

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

A

It wont absorb the IR radiation

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12
Q

What are the 4 modes of CO2?

A

Symmetric stretch
Bending motion
Asymmetric stretch
Bending motion

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13
Q

Which modes of CO2 are IR active?

A

Bending

Asymmetric

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14
Q

What are the features of a symmetric vibration?

A

No dipole moment change

IR inactive

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15
Q

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

A

3N-5

N is the number of atoms

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16
Q

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

A

3N-6

N is the number of atoms

17
Q

What do translation and rotation modes add to?

18
Q

What do vibrational modes of H2O all lead to?

A

A change in dipole moment

19
Q

What are the three modes of H2O?

A

Bending
Symmetric
Antisymmetric

20
Q

Are the H2O nodes IR active or inactive?

21
Q

How many modes of vibration do translations have?

22
Q

How many modes of vibrations do rotations have?

23
Q

What are the 6 molecular motions?

A
Symmetrical stretching 
Antisymmetrical stretching 
Scissoring 
Rocking 
Wagging 
Twisting
24
Q

Which molecular motions are found at higher frequencies?

A

symmetric stretch

Asymmetric stretch

25
What are vibronic transitions?
Change in the vibrational level during an electronic transition
26
When is the equilibrium bond length longer?
In an electronically excited state
27
What is the stokes shift?
The difference in wavelength between λmax in the fluorescence spectrum and λmax in the absorption spectrum
28
what is absorption and fluorescence in the solution phase able to do?
Reduce in level without emitting a proton