IR and Raman spectroscopy

Question 1

What is the transition seen in UV/VIS spectroscopy?

Answer 1

Excitation of valence electrons

Question 2

What is the transition seen in IR and Raman spectrocopy?

Answer 2

Excitation of vibrations

Question 3

What is the transition seen in microwave/IR spectroscopy?

Answer 3

Excitation of rotations

Question 4

What is the equation for speed of light (c)?

Answer 4

c= wavelength (metres) X frequency (Hz or s-1)

Question 5

What are the 3 ways in which a molecule can move?

Answer 5

Rotation
Translation
Vibration

Question 6

How do you work out number of vibrational modes?

Degrees of freedom

Answer 6

3 x number atoms - 6 = non-linear

3 x number atoms - 5 = linear

Question 7

What happens to frequency with increasing bond strength?

Answer 7

Frequency increases

Question 8

What happens to frequency with increasing mass?

Answer 8

Decreases

Question 9

What radiation does Raman spectroscopy uses?

Answer 9

Visible light

Question 10

What side of the infrared spectra is the diagnostic region?

Answer 10

The left side

Question 11

What side of the infrared spectra is the fingerprint region?

Answer 11

The right side

Question 12

Principles of IR spectroscopy

Answer 12

IR beam emitted towards splitter
splitter directs beam to fixed and movable mirrors
beam recombines, causing interference and is directed to sample
some of the IR absorbed rest measured by detector

Question 13

What does an almost 100% transmittance mean?

Answer 13

That almost all of that wavelength is not being absorbed

Question 14

What is the stokes line?

Answer 14

When the frequency of emitted photon is lower than frequency of incident photon.
Energy has been absorbed

Question 15

What is the anti-stokes line?

Answer 15

When the frequency of emitted photon is higher than that of incident photon
Energy has been released

Question 16

What is the rayleigh line?

Answer 16

When frequency of emitted photon is equal to incident photon

Question 17

What line is the most abundant on Raman?

Rayleigh, Stokes, Anti-stokes

Answer 17

Rayleigh

Question 18

What can the intensity of Raman lines be used to calculate?

Answer 18

The concentration

Question 19

What does Raman spectroscopy measure?

Answer 19

The emission of scattered light

Question 20

Do heavier molecules have lower or higher wavenumbers in IR spectroscopy?

Answer 20

vibrate at lower frequencies.

Question 21

Does frequency increase or decrease with increasing bond strength?

Answer 21

Increase

Question 22

Does frequency increase or decrease with increasing mass?

Answer 22

Decrease

Question 23

What does IR spectroscopy tell us?

Answer 23

What functional groups are present

Question 24

Does the frequency of vibration increase or decrease in this sequence?
Asym stretch - sysm. stretch -bend

Answer 24

Decreases from left to right

Question 25

Basic principles of raman spectroscopy

Answer 25

Source of visible light
scattering from sample
Detector of visible light.

Question 26

What is the most common type of Raman scattering?

Answer 26

Rayleigh scattering

Question 27

Does IR measure absorption or emission?

Answer 27

Absorption

Question 28

Does Raman measure absorption or emission?

Answer 28

Emission

Question 29

What type of samples can you use in IR?

Answer 29

Non-aqueous

Question 30

What does IR require?

Answer 30

A dipole moment change - so good for showing polar bonds

Question 31

What does Raman require?

Answer 31

The polarisabilty of the molecule to change during vibration