Joe Beames

Question 1

Lamba Doublet propensity

Answer 1

• 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

Question 2

Describe the three key features that a bound

wavefunction must possess which helps solve this iterative problem

Answer 2

• must be continuous
• derivative must be continuous
• must tend to zero far into the classically forbidden region

Question 3

Mechanical anharmonicity

Answer 3

deviation of the potential energy surface from that of a harmonic oscillator. Vibrational wavefunction are no longer symmetric around re

Question 4

Electrical anharmonicity

Answer 4

arises from non-linear changes in the variation of the dipole moment with atomic displacement.

Question 5

Hund’s case a)

Answer 5

Spin-orbit coupling is strong, and spin is coupled to rotation, such that J is a good quantum number

Question 6

Hund’s case b)

Answer 6

Spin orbit coupling is weaker, and the energy levels are better described by N (N = J+S)

Question 7

Polanyi’s rules

Answer 7

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

Question 8

Electronic selection rule

Answer 8

• 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

Question 9

What dictates the intensity of the vibrational intensities?

Answer 9

-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.

Question 10

Optically bright

Answer 10

Allowed transition

Question 11

Optically dark

Answer 11

forbidden transition, symmetry forbidden

Question 12

How to access the forbidden transition

Answer 12

Use the symmetry of the vibrations of the molecule to access the symmetry forbidden state

Question 13

Adiabatic representation of PES

Answer 13

Electronic configuration can vary as
a function of nuclear coordinates.
States constructed from the ground
state upwards.

Question 14

Diabatic representation of PES

Answer 14

Single electronic configuration
propagated as a function of nuclear
coordinates

Question 15

Non-crossing rule

Answer 15

In an adiabatic representation, states of the same symmetry do not cross
In a diabatic representation states can cross

Question 16

Advantages of a laser source

Answer 16

• 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

Question 17

LASER acronym

Answer 17

Light Amplification by Stimulated Emission of Radiation

Question 18

Cavity ring down spectroscopy

Answer 18

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.

Question 19

LASER action

Answer 19

-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