The Rydberg states of an
atom
Atoms are the basic particles of the chemical elements. An atom consists of a atomic nucleus, nucleus of protons and generally neutrons, surrounded by an electromagnetically bound swarm of electrons. The chemical elements are distinguished fr ...
or
molecule
A molecule is a group of two or more atoms that are held together by Force, attractive forces known as chemical bonds; depending on context, the term may or may not include ions that satisfy this criterion. In quantum physics, organic chemi ...
are electronically
excited state
In quantum mechanics
Quantum mechanics is the fundamental physical Scientific theory, theory that describes the behavior of matter and of light; its unusual characteristics typically occur at and below the scale of atoms. Reprinted, Add ...
s with energies that follow the
Rydberg formula
In atomic physics, the Rydberg formula calculates the wavelengths of a spectral line in many chemical elements. The formula was primarily presented as a generalization of the Balmer series for all atomic electron transitions of hydrogen. It was ...
as they converge on an ionic state with an
ionization energy
In physics and chemistry, ionization energy (IE) is the minimum energy required to remove the most loosely bound electron of an isolated gaseous atom, Ion, positive ion, or molecule. The first ionization energy is quantitatively expressed as
: ...
. Although the Rydberg formula was developed to describe atomic energy levels, it has been used to describe many other systems that have electronic structure roughly similar to atomic hydrogen. In general, at sufficiently high
principal quantum number
In quantum mechanics, the principal quantum number (''n'') of an electron in an atom indicates which electron shell or energy level it is in. Its values are natural numbers (1, 2, 3, ...).
Hydrogen and Helium, at their lowest energies, have just ...
s, an excited electron-ionic core system will have the general character of a
hydrogenic system and the energy levels will follow the Rydberg formula. Rydberg states have energies converging on the energy of the ion. The ionization energy threshold is the energy required to completely liberate an
electron
The electron (, or in nuclear reactions) is a subatomic particle with a negative one elementary charge, elementary electric charge. It is a fundamental particle that comprises the ordinary matter that makes up the universe, along with up qua ...
from the ionic core of an atom or molecule. In practice, a Rydberg
wave packet
In physics, a wave packet (also known as a wave train or wave group) is a short burst of localized wave action that travels as a unit, outlined by an Envelope (waves), envelope. A wave packet can be analyzed into, or can be synthesized from, a ...
is created by a laser pulse on a hydrogenic atom and thus populates a superposition of Rydberg states. Modern investigations using pump-probe experiments show molecular pathways – e.g. dissociation of
(NO)2 – via these special states.
Rydberg series
Rydberg series describe the energy levels associated with partially removing an electron from the ionic core. Each
Rydberg series converges on an ionization
energy
Energy () is the physical quantity, quantitative physical property, property that is transferred to a physical body, body or to a physical system, recognizable in the performance of Work (thermodynamics), work and in the form of heat and l ...
threshold associated with a particular ionic core configuration. These quantized Rydberg energy levels can be associated with the quasiclassical Bohr atomic picture. The closer you get to the ionization threshold energy, the higher the principal quantum number, and the smaller the energy difference between "near threshold Rydberg states." As the electron is promoted to higher energy levels, the spatial excursion of the electron from the ionic core increases and the system is more like the
Bohr quasiclassical picture.
Energy of Rydberg states
The energy of Rydberg states can be refined by including a
correction
Correction may refer to:
* A euphemism for punishment
* Correction (newspaper), the posting of a notice of a mistake in a past issue of a newspaper
* Correction (stock market), in financial markets, a short-term price decline
* ''Correction'' (n ...
called the quantum defect in the Rydberg formula. The "quantum defect" correction is associated with the presence of a distributed ionic core. Even for many electronically excited molecular systems, the ionic core interaction with an excited electron can take on the general aspects of the interaction between the
proton
A proton is a stable subatomic particle, symbol , Hydron (chemistry), H+, or 1H+ with a positive electric charge of +1 ''e'' (elementary charge). Its mass is slightly less than the mass of a neutron and approximately times the mass of an e ...
and the electron in the
hydrogen
Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...
atom. The spectroscopic assignment of these states follows the Rydberg formula and they are called Rydberg states of molecules.
Molecular Rydberg states
Although the energy formula of Rydberg series is a result of hydrogen-like atom structure, Rydberg states are also present in molecules.
Wave functions
In quantum physics, a wave function (or wavefunction) is a mathematical description of the quantum state of an isolated quantum system. The most common symbols for a wave function are the Greek letters and (lower-case and capital psi, respec ...
of high Rydberg states are very diffuse and span diameters that approach infinity.{{Vague, date=September 2021 As a result, any isolated neutral molecule behaves like a
hydrogen-like atom
A hydrogen-like atom (or hydrogenic atom) is any atom or ion with a single valence electron. These atoms are isoelectronic with hydrogen. Examples of hydrogen-like atoms include, but are not limited to, hydrogen itself, all alkali metals such as ...
at the Rydberg limit. For molecules with multiple stable
monovalent cations, multiple Rydberg series may exist. Because of the complexity of molecular spectra, low-lying Rydberg states of molecules are often mixed with valence states with similar energy and are thus not pure Rydberg states.
[Stohr, J., "NEXAFS Spectroscopy" Springer Series in Surface Science 25, (1992), p. 86.]
See also
*
Rydberg atom
A Rydberg atom is an excited atom with one or more electrons that have a very high principal quantum number, ''n''. The higher the value of ''n'', the farther the electron is from the nucleus, on average. Rydberg atoms have a number of peculi ...
*
Rydberg matter
Rydberg matter is an exotic phase of matter formed by Rydberg atoms; it was predicted around 1980 by É. A. Manykin, M. I. Ozhovan and P. P. Poluéktov. It has been formed from various elements like caesium, potassium, hydrogen and nitrogen; s ...
*
Orbital state
References
* Atomic Spectra and Atomic Structure, Gerhard Herzberg, Prentice-Hall, 1937.
* Atoms and Molecules, Martin Karplus and Richard N. Porter, Benjamin & Company, Inc., 1970.
External links
Army Creates Quantum Sensor That Detects Entire Radio-Frequency Spectrum Defense One.
Physics Department, Davidson College.
Chemistry and Biochemistry, Georgia Tech.
Atomic physics
Atomic, molecular, and optical physics