Electromagnetic radiation is a form of energy that travels in waves. Specifically, electromagnetic energy travels in a transverse wave that oscillates at a certain frequency. The name “electromagnetic” refers to the electric and magnetic field components that constitute the radiative energy. Electromagnetic radiation travels at a particular speed (the speed of light) and its frequency and wavelength are inversely related to one another; as one increases, the other decreases. This relationship is highlighted in the equation below.
Electromagnetic radiation ranges from extremely energetic (gamma rays) to relatively low energy (long radio waves). The equation that relates energy to the frequency of light is given above.
Visible light is a type of electromagnetic radiation. Light, like all electromagnetic radiation, travels in discrete packages called photons. A beam of light is not a single entity, but is rather composed of numerous photons.
The interaction between molecules and electromagenetic radiation are critical for many important processes, including molecular excitation.
Photons are the smallest, discrete unit of electromagnetic radiation possible. A photon has an electric field component that is perpendicular to its magnetic field component. These two components are also traveling waves that are always in phase with one another (two waves are in phase when their highest points and lowest points are perfectly aligned) and are always perpendicular to the direction the wave is traveling. The orientation of these waves have a large impact on how they interact with other waves or particles.
Below is a presentation of the photon as a sphere. The orientation of the electric and magnetic fields are represented by differently shaded planes
Try changing the color of light. Notice how the frequency and wavelength of the light changes as you shift the colour. You can drag the photon and electromagnetic fields to explore the model in three dimensions.
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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.