Another contribution to the quantized energy of the diatomic molecule is its rotational energy. In the diatomic system, there exists a single rotational mode, similar to how a single vibrational mode exists for the diatomic molecule. Also, just like the vibrational state, a more complicated system (ie. a molecular with more than two atoms) would have multiple rotation states.
The observed rotation is due to the specific angular momentum of the diatomic molecule. Quantum mechanics is used to determine the allowed angular momentum states. The magnitude of the rotational energy is considerably smaller than the vibrational energy, as can be observed in the diagram above.
For our diatomic molecule only a single rotational mode available is available and it occurs about an axis perpendicular to the bond axis. The energy of the rotational mode is directly related to its angular momentum. Molecular rotation takes place at a nanosecond time scale (~10-9s).
Molecules can gain and lose energy from their surroundings which can change both the systems vibrational or rotational energy. Another source of energy is electromagnetic radiation. In fact, electromagnetic radiation is capable of promoting electrons to an excited state.
In the system to the left, you can alter both the current rotational mode and vibrational state by clicking on the selector, clicking on the π bond, or clicking on the vibration/rotation energy state. You can also switch molecular vibration and rotation 'on' or 'off'. What do you notice when you increase the rotational mode? What would you expect to happen as a molecule loses energy?
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.