Microwave Spectroscopy Flashcards
Angular momentum’s of photons
Fixed
What does a dipole placed in oscillating field experience
Rotational force
Physical mechanism behind IR/microwave spectroscopy
Vibration/rotation of nuclei involves motion of electron clouds which are unevenly distributed so motions of nuclei cause oscillating charge distributions which can emit or absorb light
Microwave gross selection rule
Needs dipole doesn’t equal zero
Microwave spectroscopy specific selection rule
Δj = +-1
Upper j symbol
J’
Lower j symbol
J”
Rotational transition spacing
Lines evenly spaced by 2B if molecules a rigid rotor
What does intensity depend on
Concentration, how many molecules there are in correct energy level and how likely it is for a photon to be absorbed
Gross selection rules for microwave spectroscopy of non-linear molecules
Must have a non-zero dipole moment
Specific selection rules for microwave spectroscopy of non-linear molecules
Symmetric: ΔJ = +-1, ΔK = 0, Δmj = 0, +-1
Physical mechanism for vibrational transitions
As molecule vibrates dipole moment changes, stretch = dipole increases, contracts = dipole decreases and this oscillating dipole interacts with electromagnetic field
Range of mj
+j to -j in integer steps
How does the moment of inertia and therefore the rotational constant of a diatomic molecule change with increasing vibrational level
moment of inertia of a diatomic molecule increases with increasing vibrational quantum number
average bond length increases as the vibrational energy increases
Rotational constant is inversely proportional to the moment of inertia
Therefore decreases with increasing quantum number
Can K be more than j
No as it’s a projection of j onto the internal axis of the molecule
