Joe Beames Flashcards
Lamba Doublet propensity
- Coupling of the single electron in a p-orbital with nuclear rotation
- Electron could be in the orbital in plane of rotation OR in an orbital perpendicular to plane of rotation
- Leads to the splitting in energy levels
- More rotation causes more splitting
Describe the three key features that a bound
wavefunction must possess which helps solve this iterative problem
- must be continuous
- derivative must be continuous
- must tend to zero far into the classically forbidden region
Mechanical anharmonicity
deviation of the potential energy surface from that of a harmonic oscillator. Vibrational wavefunction are no longer symmetric around re
Electrical anharmonicity
arises from non-linear changes in the variation of the dipole moment with atomic displacement.
Hund’s case a)
Spin-orbit coupling is strong, and spin is coupled to rotation, such that J is a good quantum number
Hund’s case b)
Spin orbit coupling is weaker, and the energy levels are better described by N (N = J+S)
Polanyi’s rules
Polanyi’s rules state that vibrational energy is more efficient in promoting a late barrier reaction than translational energy, whereas for an early-barrier reaction the reverse is true for overcoming the energy barrier. I
Electronic selection rule
- transition between initial and final wavefuntion is mediated by the transition dipole moment.
- Integrating over both wavefunctions and transition dipole moment; if non-zero, transition can occur
- In symmetry terms, the transition can occur if the product of all three add up to a totally symmetric wavefunction
What dictates the intensity of the vibrational intensities?
-Due to Frank-Condon factors
A change from one vibrational energy level to another will be more likely to happen if the two vibrational wave functions overlap more significantly.
Optically bright
Allowed transition
Optically dark
forbidden transition, symmetry forbidden
How to access the forbidden transition
Use the symmetry of the vibrations of the molecule to access the symmetry forbidden state
Adiabatic representation of PES
Electronic configuration can vary as
a function of nuclear coordinates.
States constructed from the ground
state upwards.
Diabatic representation of PES
Single electronic configuration
propagated as a function of nuclear
coordinates
Non-crossing rule
In an adiabatic representation, states of the same symmetry do not cross
In a diabatic representation states can cross
Advantages of a laser source
- Can have exceptionally high powers (greater than the sun)
- Can provide very short pulses of intense light (< 1x10-12 s)
- Light they provide is coherent, and can readily be collimated
- Coherent output can be polarised (both linear and circular)
- Can provide very narrow bandwidth output (MHz)
- Can be exceptionally stable
LASER acronym
Light Amplification by Stimulated Emission of Radiation
Cavity ring down spectroscopy
To use absorption spec, very insensitive, must be able to detect a small change in a large signal. Can be problematic as we cannot change the epsilon value and conc in laser, however we can change length;
to do this we bounce the laser of mirrors back and fourth through the sample increasing path length
can now detect tiny concentrations
Also completely insensitive to to fluxuation in light source, and can make very sensitive measurements. Rate of decay of intensity can be related to absorption.
LASER action
-Need to create a lot of stimulated emission
-population of two states in a closed state, upper state can never be populated over 50%
-Therefore can never make a population inversion that is required for a laser
-Introduce another state (3 states), makes a population inversion between top state and middle state
-The excited state may spontaneously emit (fluorescence)
-Spontaneous emission may induce stimulated emission in another pumped molecule → amplifying the number of
photons
