All Topics  
Excited state

 

 
   Email Print
   Bookmark   Link
 

 

Excited state
 
 
  Topics Excited state Topic Home

Excitation is an elevation in energy level above an arbitrary baseline energy state. In physics there is a specific technical definition for energy level
Energy level

A Quantum mechanics system or particle that is Bound state, confined spatially, can only take on certain discrete values of energy, as opposed to Classical mechanics particles, which can have any energy....
 which is often associated with an atom being excited to an excited state.

In quantum mechanics
Quantum mechanics

Quantum mechanics is a set of principles underlying the most fundamental known description of all physical systems at the microscopic scale . Notable amongst these principles are both a dual wave-like and particle-like behavior of matter and radiation, and prediction of probabilities in situations where classical physics predicts certaintie...
 an excited state of a system (such as an atom
Atom

|-! bgcolor=gray | Properties|-||}The atom is a basic unit of matter consisting of a dense, central atomic nucleus surrounded by a electron cloud of electric charge electrons....
, molecule
Molecule

In chemistry, a molecule is defined as a sufficiently stable, electric charge neutral group of at least two atoms in a definite arrangement held together by very strong chemical bonds....
 or nucleus
Atomic nucleus

The nucleus of an atom is the very dense region, consisting of nucleons , at the center of an atom. Although the size of the nucleus varies considerably according to the mass of the atom, the size of the entire atom is comparatively constant....
) is any quantum state
Quantum state

In quantum physics, a quantum State is a mathematical object that fully describes a Quantum system. One typically imagines some experimental apparatus and procedure which "prepares" this quantum state; the mathematical object then reflects the setup of the apparatus....
 of the system that has a higher energy
Energy

In physics, energy is a scalar physical quantity that describes the amount of Work_ that can be performed by a force. Energy is an attribute of objects and systems that is subject to a conservation law....
 than the ground state (that is, more energy than the absolute minimum). The temperature
Temperature

In physics, temperature is a physical property of a Physical system that underlies the common notions of hot and cold; something that feels hotter generally has the greater temperature....
 of a group of particles is indicative of the level of excitation.

The lifetime of a system in an excited state is usually short: spontaneous
Spontaneous emission

Spontaneous emission is the process by which a light source such as an atom, molecule, nanocrystal or atomic nucleus in an excited state undergoes a transition to the ground state and emits a photon....
 or induced emission
Stimulated emission

In optics, stimulated emission is the process by which an electron, perturbed by a photon having the correct energy, may drop to a lower energy level resulting in the creation of another photon....
 of a quantum of energy (such as a photon
Photon

In physics, the photon is an elementary particle, the quantum of the electromagnetic field and the basic unit of light and all other forms of electromagnetic radiation....
 or a phonon
Phonon

In physics, a phonon is a quantum mode of vibration occurring in a rigid crystal structure, such as the atomic lattice of a solid. The study of phonons is an important part of solid state physics, because phonons play a major role in many of the physical properties of solids, including a material's thermal conductivity and electrical conduc...
) usually occurs shortly after the system is promoted to the excited state, returning the system to a state with lower energy (a less excited state or the ground state).






Discussion
Ask a question about 'Excited state'
Start a new discussion about 'Excited state'
Answer questions from other users
Full Discussion Forum



Encyclopedia


Energylevels
Excitation is an elevation in energy level above an arbitrary baseline energy state. In physics there is a specific technical definition for energy level
Energy level

A Quantum mechanics system or particle that is Bound state, confined spatially, can only take on certain discrete values of energy, as opposed to Classical mechanics particles, which can have any energy....
 which is often associated with an atom being excited to an excited state.

In quantum mechanics
Quantum mechanics

Quantum mechanics is a set of principles underlying the most fundamental known description of all physical systems at the microscopic scale . Notable amongst these principles are both a dual wave-like and particle-like behavior of matter and radiation, and prediction of probabilities in situations where classical physics predicts certaintie...
 an excited state of a system (such as an atom
Atom

|-! bgcolor=gray | Properties|-||}The atom is a basic unit of matter consisting of a dense, central atomic nucleus surrounded by a electron cloud of electric charge electrons....
, molecule
Molecule

In chemistry, a molecule is defined as a sufficiently stable, electric charge neutral group of at least two atoms in a definite arrangement held together by very strong chemical bonds....
 or nucleus
Atomic nucleus

The nucleus of an atom is the very dense region, consisting of nucleons , at the center of an atom. Although the size of the nucleus varies considerably according to the mass of the atom, the size of the entire atom is comparatively constant....
) is any quantum state
Quantum state

In quantum physics, a quantum State is a mathematical object that fully describes a Quantum system. One typically imagines some experimental apparatus and procedure which "prepares" this quantum state; the mathematical object then reflects the setup of the apparatus....
 of the system that has a higher energy
Energy

In physics, energy is a scalar physical quantity that describes the amount of Work_ that can be performed by a force. Energy is an attribute of objects and systems that is subject to a conservation law....
 than the ground state (that is, more energy than the absolute minimum). The temperature
Temperature

In physics, temperature is a physical property of a Physical system that underlies the common notions of hot and cold; something that feels hotter generally has the greater temperature....
 of a group of particles is indicative of the level of excitation.

The lifetime of a system in an excited state is usually short: spontaneous
Spontaneous emission

Spontaneous emission is the process by which a light source such as an atom, molecule, nanocrystal or atomic nucleus in an excited state undergoes a transition to the ground state and emits a photon....
 or induced emission
Stimulated emission

In optics, stimulated emission is the process by which an electron, perturbed by a photon having the correct energy, may drop to a lower energy level resulting in the creation of another photon....
 of a quantum of energy (such as a photon
Photon

In physics, the photon is an elementary particle, the quantum of the electromagnetic field and the basic unit of light and all other forms of electromagnetic radiation....
 or a phonon
Phonon

In physics, a phonon is a quantum mode of vibration occurring in a rigid crystal structure, such as the atomic lattice of a solid. The study of phonons is an important part of solid state physics, because phonons play a major role in many of the physical properties of solids, including a material's thermal conductivity and electrical conduc...
) usually occurs shortly after the system is promoted to the excited state, returning the system to a state with lower energy (a less excited state or the ground state). This return to a lower energy level is often loosely described as decay and is the inverse of excitation.

Long-lived excited states are often called metastable. Long-lived nuclear isomer
Nuclear isomer

A nuclear isomer is a metastable state of an atomic nucleus caused by the excited state of one or more of its nucleons. A nuclear isomer occupies a higher energy state than the corresponding non-excited nucleus, called the ground state....
s and singlet oxygen
Singlet oxygen

Singlet oxygen is the common name used for the diamagnetic form of molecular oxygen , which is less stable than the normal triplet oxygen. Because of its unusual properties, singlet oxygen can persist for over an hour at room temperature, depending on the environment....
 are two examples of this.

Atomic excitation

A simple example of this concept comes by considering the hydrogen atom
Hydrogen atom

A hydrogen atom is an atom of the chemical element hydrogen. The Electric charge neutral atom contains a single positively-charged proton and a single negatively-charged electron bound to the nucleus by the Coulomb force....
.

The ground state of the hydrogen atom corresponds to having the atom's single electron
Electron

The electron is a subatomic particle that carries a negative electric charge. It has elementary particle and is believed to be a point particle....
 in the lowest possible orbit
Atomic orbital

An atomic orbital is a mathematical function that describes the wave-like behavior of an electron in an atom. This function can be used to calculate the probability of finding any electron of an atom in any specific region around the atom's nucleus....
 (that is, the spherically symmetric "1s" wavefunction
Wavefunction

A wave function or wavefunction is a mathematical tool used in quantum mechanics to describe any physical system. It is a function from a mathematical space that maps the possible states of the system into the complex numbers....
, which has the lowest possible quantum number
Quantum number

Quantum numbers describe values of conserved numbers in the dynamics of the quantum system. They often describe specifically the energies of electrons in atoms, but other possibilities include angular momentum, Spin etc....
s). By giving the atom additional energy (for example, by the absorption of a photon
Photon

In physics, the photon is an elementary particle, the quantum of the electromagnetic field and the basic unit of light and all other forms of electromagnetic radiation....
 of an appropriate energy), the electron is able to move into an excited state (one with one or more quantum numbers greater than the minimum possible). If the photon has too much energy, the electron will cease to be bound
Bound state

In physics, a bound state is a composite of two or more building blocks that behaves as a single object. In quantum mechanics , a bound state is a state in the Hilbert space that corresponds to two or more particles whose interaction energy is negative, and therefore these particles cannot be separated unless energy is spent....
 to the atom, and the atom will become ion
Ion

An ion is an atom or molecule which has lost or gained one or more electrons, giving it a positive or negative electrical charge. According to the Bohr_model this will be from or in the outer shield 'n'....
ised.

After excitation the atom may return to a lower excited state, or the ground state, by emitting a photon with a characteristic energy. Emission of photons from atoms in various excited states leads to an electromagnetic spectrum
Electromagnetic spectrum

The electromagnetic spectrum is the range of all possible electromagnetic radiation frequencies. The "electromagnetic spectrum" of an object is the characteristic distribution of electromagnetic radiation from that particular object....
 showing a series of characteristic emission lines (including, in the case of the hydrogen atom, the Lyman, Balmer, Paschen and Brackett series
Hydrogen spectral series

The emission spectrum of hydrogen is divided into a number of series. In physics, the spectral lines of hydrogen correspond to particular jumps of the electron between energy levels....
.)

An atom in a high excited state is termed Rydberg atom
Rydberg atom

A Rydberg atom is an excited state with one or more electrons that have a very high principal quantum number. These atoms have a number of peculiar properties including an exaggerated response to Electric field and magnetic fields, long decay periods and electron wavefunctions that approximate, under some conditions, Classical physics orbits...
. A system of highly excited atoms can form a long-lived condensed excited state e.g. a condensed phase made completely of excited atoms: Rydberg matter
Rydberg matter

Rydberg matter is a metastable state of highly excited atoms and molecules which are condensed in a solid- or liquid-like very low density matter....
. Hydrogen can also be excited by heat or electricity.

Perturbed gas excitation

A collection of molecules forming a gas can be considered in an excited state if one or more molecules are elevated to kinetic energy levels such that the resulting velocity distribution departs from the equilibrium Maxwell-Boltzmann distribution. This phenomenon has been studied in the case of a two-dimensional gas
Two-dimensional gas

A two-dimensional gas is a collection of N objects which are constrained to move in a planar or other two-dimensional space in a gaseous state. The objects can be: ideal gas elements such as rigid Disk undergoing elastic collisions; elementary particles, or any object in physics which obeys laws of motion....
 in some detail, analyzing the time taken to relax to equilibrium.

See also

  • Rydberg formula
    Rydberg formula

    The Rydberg formula is used in atomic physics to describe the wavelengths of spectral lines of many chemical elements. The formula was invented by the Swedish physicist Johannes Rydberg and presented on November 5, 1888....
  • Stationary state
    Stationary state

    In quantum mechanics, a stationary state is an eigenstate of a Hamiltonian , or in other words, a state of definite energy. It is called stationary because the corresponding probability density has no time dependence....


External links