Potential energy surfaces and hydrogen Flashcards
the Born-Oppenheimer approximation
mp/me = 1836
Total potential energy according to the BO approximation
V = Vee + Vnn - Ven
Vee = electron repulsion
Vpp = proton repulsion
Vep = electron-proton attraction
force experienced by nuclei
F = -dV/dx
where
V = 1/2kx^2
or
V = De(1-e^(-alpha*x))^2
When does tunnelling occur
Occurs when a reaction still takes place despite the fact the energy is less than the Ea requirement
When is tunnelling most relevent
For light atoms with the most wavelike properties
Hydrogen emission spectra
Lyman (UV) from n = 1
Balmer (vis) from n = 2
Paschen (IR)
What happens each series with frequency
As frequency decreases, the lines in each series converge to a maximum. Energy gap tends towards 0
Allowed energy levels of hydrogen
En = - hcRh/(n^2)
Hydrogen’s ionisation energy
The ionization energy to remove a ground state electron I.E. the energy of a ground state electron
energy gap for hydrogen atoms
dE = hcRh(1/n1^2 - 1/n2^2)
The Frank-Condon principle
Electrons will excite and relax before the nuclei can respond to external stimuli. Therefore, the strongest transition is the one with the most vertical overlap between ground and excited PE curve
Frank-Condon overlap rules
If excited bond length is equal to ground bond length, the greatest overlap will be between the ground vibrational states of each. If the excited bond length is longer, the greatest overlap is between the ground state and the excited vibrational modes of the excited state.
Allowed energy levels of conjugated molecules
The same as a particle in a box.
E = n^2h^2/8mL^2
Typical wavelengths of HOMO-LUMO transitions
UV region for short chain
visible region for long/conjugated chains
Beer Lambert law
log10(I0/I) = epsCl = A
