IR and Raman spectroscopy Flashcards
What is the transition seen in UV/VIS spectroscopy?
Excitation of valence electrons
What is the transition seen in IR and Raman spectrocopy?
Excitation of vibrations
What is the transition seen in microwave/IR spectroscopy?
Excitation of rotations
What is the equation for speed of light (c)?
c= wavelength (metres) X frequency (Hz or s-1)
What are the 3 ways in which a molecule can move?
Rotation
Translation
Vibration
How do you work out number of vibrational modes?
Degrees of freedom
3 x number atoms - 6 = non-linear
3 x number atoms - 5 = linear
What happens to frequency with increasing bond strength?
Frequency increases
What happens to frequency with increasing mass?
Decreases
What radiation does Raman spectroscopy uses?
Visible light
What side of the infrared spectra is the diagnostic region?
The left side
What side of the infrared spectra is the fingerprint region?
The right side
Principles of IR spectroscopy
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
What does an almost 100% transmittance mean?
That almost all of that wavelength is not being absorbed
What is the stokes line?
When the frequency of emitted photon is lower than frequency of incident photon.
Energy has been absorbed
What is the anti-stokes line?
When the frequency of emitted photon is higher than that of incident photon
Energy has been released
What is the rayleigh line?
When frequency of emitted photon is equal to incident photon
What line is the most abundant on Raman?
Rayleigh, Stokes, Anti-stokes
Rayleigh
What can the intensity of Raman lines be used to calculate?
The concentration
What does Raman spectroscopy measure?
The emission of scattered light
Do heavier molecules have lower or higher wavenumbers in IR spectroscopy?
vibrate at lower frequencies.
Does frequency increase or decrease with increasing bond strength?
Increase
Does frequency increase or decrease with increasing mass?
Decrease
What does IR spectroscopy tell us?
What functional groups are present
Does the frequency of vibration increase or decrease in this sequence?
Asym stretch - sysm. stretch -bend
Decreases from left to right
Basic principles of raman spectroscopy
Source of visible light
scattering from sample
Detector of visible light.
What is the most common type of Raman scattering?
Rayleigh scattering
Does IR measure absorption or emission?
Absorption
Does Raman measure absorption or emission?
Emission
What type of samples can you use in IR?
Non-aqueous
What does IR require?
A dipole moment change - so good for showing polar bonds
What does Raman require?
The polarisabilty of the molecule to change during vibration
