What is Franck-Condon principle explain?
The Franck–Condon principle is a rule in spectroscopy and quantum chemistry that explains the intensity of vibronic transitions. Vibronic transitions are the simultaneous changes in electronic and vibrational energy levels of a molecule due to the absorption or emission of a photon of the appropriate energy.
What are the types of electronic transitions?
There are three types of electronic transition which can be considered;
- Transitions involving p, s, and n electrons.
- Transitions involving charge-transfer electrons.
- Transitions involving d and f electrons (not covered in this Unit)
What is vibrational progression?
Vibronic progression means that there is a coupling to vibrational modes in a polymer or oligomer resulting in excitation from the ground state to the excited state, or emission from the excited state down to the ground state.
What is the Franck-Condon envelope?
The Franck-Condon Principle describes the intensities of vibronic transitions, or the absorption or emission of a photon. It states that when a molecule is undergoing an electronic transition, such as ionization, the nuclear configuration of the molecule experiences no significant change.
What are the selection rule for allowed transitions?
The only allowed transitions are those in which the orbital quantum number of an electron changes by one and its magnetic quantum number remains the same or changes by one. Radiations not meeting these selection rules are rarely observed.
What are electron transitions allowed?
As an illustration of allowed transition in Figure 1, the only electronic transitions permitted are those in which the change in vibrational quantum number accompanying a change in electronic excitation is plus or minus one or zero, except that a 0 ↔ 0 (zero-to-zero) change is not permitted.
What are the types of electronic transitions with examples?
How do electronic transitions occur?
Molecular electronic transitions take place when electrons in a molecule are excited from one energy level to a higher energy level. The energy change associated with this transition provides information on the structure of a molecule and determines many molecular properties such as colour.
Why is the Franck-Condon shift called the Stokes shift?
The energy emitted EB is lower than the energy absorbed EA. The difference between these two energies is called the Franck–Condon shift. In general, the degradation of optical energy is called the Stokes shift. Thus, the Franck–Condon shift is a Stokes shift due to the displacement of the molecule Δ r.
How is the Franck Condon principle used in spectroscopy?
Franck-Condon principle. The Franck-Condon principle is a rule in spectroscopy and quantum chemistry that explains the intensity of vibronic transitions. Vibronic transitions are the simultaneous changes in electronic and vibrational energy levels of a molecule due to the absorption or emission of a photon of the appropriate energy.
Why are electronic transitions favored by the Franck-Condon principle?
Franck–Condon principle energy diagram. Since electronic transitions are very fast compared with nuclear motions, vibrational levels are favored when they correspond to a minimal change in the nuclear coordinates. The potential wells are shown favoring transitions between v = 0 and v = 2.
Which is the absorption at the Franck Condon maximum?
EA is the absorption at the Franck–Condon maximum, and EB is the emission at the Franck–Condon minimum; r is the nuclear separation. The energy emitted EB is lower than the energy absorbed EA. The difference between these two energies is called the Franck–Condon shift.