We can approximate the energy of our diatomic using the Morse Potential we have encountered earlier (we are ignoring the quantum nature of the molecule for now).
We have simultaneously shown the potential energies of the π and π* orbitals below. If an electron were to transfer from the π to the higher energy π* orbital, it is said to have been promoted to an excited state. This process is known as molecular excitation. We can determine the change in energy by taking the difference in potential energy before and after the excitation event.
Molecular excitation is not a random event and requires strict conditions in order to occur. Before we can learn more about molecular excitation, we must first understand the energy and other properties of our diatomic system.
Just like two balls on a spring, the atoms are stretched and compressed along its bond. However, unlike the spring, the energy of this system is modelled by the Morse potential like the electrostatic spheres model.
Spring, Pi, Spheres
The Morse potential is modelled by the following expression:
Grab the atom on the right and try moving it left and right. What happens to the energy as you do so? What happens if you pull the bond much further to the right? Why does the system look like this now? Why does the energy change in this way?
You will see a brief description and will be given a chance to jump directly to that topic
This topic is not currently available.
Physical chemistry attempts to understand chemistry through the physical world and using instrumentation.
Molecular excitation refers to the promotion of an electron to an excited state. This particular pheomenon is extremely important for current scientific discovery, particularly in the biological sciences.
A simple harmonic oscillator displays a very particular type of periodic motion called simple harmonic motion. A common example of a simple harmonic oscillator is a spring that is compressed or stretched.
Morse potentials are used to model the interaction between two atoms in a diatomic molecule.
A diatomic molecule has only two atoms which are connected through a chemical bond. This particular diatomic molecule is double bonded.
The energy of a diatomic molecule can be approximated using a Morse Potential. Quantum effects are not discussed.
The vibrational state of the diatomic molecule refers to the frequency at which the atoms oscillate (ie. the bond stretches and compresses).
A single rotational mode is available to the diatomic molecule and involves rotation around an axis that is perpendicular to the bond axis. The energy of the rotational mode is directly related to its angular momentum.
Electromagnetic radiation is a form of that travels in waves. Specifically, electromagnetic energy travels in a transverse wave that oscillates at a certain frequency.
Like other dipoles, the transition dipole refers to a difference in charge from one location of a molecule to another. The transition dipole occurs when an electron is excited from the ground state to an excited state.
The Jablonski diagram is capable of showing the transition between ground states and excited states by using quantized Morse potentials.
Fluorescence begins with absorption and molecular excitation into an excited state. Once promoted, the electron will fall to the lowest vibrational energy within that excited state.