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Topic: Excited state


  
  Excited state - Wikipedia, the free encyclopedia
In quantum mechanics, an excited state of a system (such as an atom, molecule or nucleus) is any quantum state of the system that has a higher energy than the ground state (that is, more energy than the absolute minimum).
The ground state of the hydrogen atom corresponds to having the atom's single electron in the lowest possible orbit (that is, the spherically symmetric "1s" wavefunction, which has the lowest possible quantum numbers).
The atom may return to a lower excited state, or the ground state, by emitting a photon with a characteristic energy.
en.wikipedia.org /wiki/Excited_state   (292 words)

  
 NationMaster.com - Encyclopedia: Excited state
Spontaneous emission is the process by which a molecule in an excited state drops to the ground state, resulting in the creation of a photon.
State densities can be calculated by adding together the densities arising from various microstates, weighted by their contribution to the overall state.
The linear combinations of microstates in the state functions are given in the output, as shown in Figure 6.10.
www.nationmaster.com /encyclopedia/Excited-state   (1012 words)

  
 Excimer - Wikipedia, the free encyclopedia
An excimer (originally short for excited dimer) is a short-lived molecule that bonds two molecules in an electronic excited state.
The wavelength of an excimer's emission is longer than that of the excited monomer's emission, because the excimer is stabilized compared to the excited monomer.
While an excimer is a molecule that forms a dimer from the same molecule in the excited state, an exciplex is a molecule that forms a dimer from different molecules in the excited state.
en.wikipedia.org /wiki/Excimer   (371 words)

  
 Theoretical Chemistry, KTH, List of publications   (Site not responding. Last check: 2007-11-02)
The excited state polarizabilities are given by the double residues of the cubic response functions.
excited state of formaldehyde is better reproduced by ground state cubic response theory than by the corresponding separate state linear response function calculation, and by that the calculations call for an experimental reinvestigation of the excited state polarizabilities of \textits-tetrazine.
A few prerequisites are given: The excited state should be isolated in energy, the ordering of the main contributing states should be reproduced, and the geometric conformation of the excited state in question should not be very different from the ground state geometry.
www.theochem.kth.se /publications/abstract.php?id=127   (227 words)

  
 [No title]   (Site not responding. Last check: 2007-11-02)
When a nucleus emits an α or β particle, the daughter nucleus is sometimes left in an excited state.
Helium II is a superfluid, a quantum-mechanical state of matter with strange properties.
For a laser to operate, the gain medium must be "pumped" by an external energy source, such as electricity or light (from a classical source such as a flash lamp, or another laser).
www.worldhistory.com /wiki/e/excited-state.htm   (841 words)

  
 Excited State Trapping and the Stepanov Relation with Reference to Photosystem I -- Jennings et al. 85 (6): 3923 -- ...   (Site not responding. Last check: 2007-11-02)
is not rapid with respect to the excited state decay.
Decay kinetics and quantum yields of fluorescence in Photosystem I from Synechococcus elongatus with P700 in the reduced and oxidized state: are the kinetics of excited state decay trap-limited or transfer-limited?
Excited state equilibration in the Photosystem I light-harvesting I complex: P700 is almost isoenergetic with its antenna.
www.biophysj.org /cgi/content/full/85/6/3923   (2618 words)

  
 Pump-Probe Spectroscopy of Ultrafast Electron Injection from the Excited State of an Anchored Chromophore to a ...
Decay of the excited state into a continuum of electronic states is examined for various energy positions of the injecting state and for different bandwidths of the continuum.
As one of the main objectives of this work, the excited state lifetime is numerically calculated from the above expression (1) for various energy positions of the excited state in the conduction band, (2) for various widths of the conduction band of the semiconductor substrate, and (3) for various dimensionalities of the semiconductor substrate.
The decay of the excited state is seen from the calculations as an irreversible one, since it is well-known that the large continuum of final states available for the electron act as a kind of an "electronic bath", making the electron transfer akin to a relaxation process.
pubs.acs.org /cgi-bin/jtextd?jpcbfk/104/i01/html/jp991428r.html   (6955 words)

  
 Cold Collisions
Colliding neutral atoms, confined in a laser trap, are photoassociated to bound excited states of the dimer molecule by absorbing a photon from a tunable laser.
The formation of the excited state is observed either by ionizing it with a second photon and detecting the ions or by detecting the loss of trapped atoms due to decay of the excited state to untrapped states.
This state is a "pure long range state" [3] which correlates at large internuclear separation with a Na ground state atom and a Na atom in its first excited state.
physics.nist.gov /Divisions/Div842/Gp4/collisions.html   (870 words)

  
 The Twin Excited State as a Probe for the Transition State in Concerted Unimolecular Reactions: The Semibullvalene ...
The Twin Excited State as a Probe for the Transition State in Concerted Unimolecular Reactions: The Semibullvalene Rearrangement**
state is the twin state of the transition state for the isomerization reaction of semibullvalene, as the three criteria identified above are fulfilled.
Since a transition from the TS to the twin-excited state is weakly Franck-Condon allowed, the signal may be weak, and the actual lifetime of this state could be shortened by a radiationless process connecting it with the ground state which may smear out the vibrational structure of the transition.
chem.ch.huji.ac.il /employee/haas/paper2/SEMIB.HTM   (2357 words)

  
 Excited state   (Site not responding. Last check: 2007-11-02)
excited state: state in which an atom or molecule picks up outside energy, causing an electron to move into a higher-energy orbital.
If excited state absorption occurs with the pump wave, the pump wavelength may be changed for...
Conventionally, the excited states are ranked in order of increasing energy; that is, the second excited state has higher energy than the first,...
www.serebella.com /encyclopedia/article-Excited_state_.html   (1893 words)

  
 CIS with Highly Symmetric Molecules
This method may be used to predict excited state structures, UV/visible spectra, adiabatic excitation energies, 0-0 transitions, electron densities, and similar properties for a wide range of molecules.
By default, when an excited state calculation is specified with the CIS keyword, Gaussian solves for the lowest three excited state of the molecule and reports on excitation energies and oscillator strengths for all three.
Because the symmetry in the initial guess is conserved, if the molecule has very high symmetry and the number of states sought is too small, then all of the symmetry types in the molecule may not be represented in the initial guess vectors, and the program may converge to a higher energy state than desired.
www.gaussian.com /g_whitepap/tn_win91.htm   (419 words)

  
 sciforums.com - Relativity in a medium
The process of returning from the excited state to the ground state with the emission of a photon in phase with the exciting electromagnetic field is referred to as stimulated emission,
Spontaneous emission from the excited state is one mechanism which limits the lifetime of the excited state.
Atoms in the excited state can decay without the presence of an external light field due to stimulation due to "zero-point fluctuations." Zero-point fluctuations are the dynamic variations in the shape of an electronic orbital at any instant in time.
www.sciforums.com /showthread.php?goto=lastpost&t=44670   (1074 words)

  
 Newsletter
In TF experiments, beam nuclei are excited by Coulomb excitation and, as they decay by a highly anisotropic gamma emission, the angular distribution of this emission is caused to rotate by their passing through a ferromagnetic metal layer in which they are subject to Larmor precession.
The attenuation is caused by Larmor precession over the lifetime of the excited state and is thus a measure of the g-factor of the excited state.
states of the Te isotopes should increase from their level of close to 0.3 at mid-shell to a sharp maximum of about 0.7 at the neutron shell closure, before falling steeply beyond the shell, possibly to negative values.
www.phy.ornl.gov /hribf/news/feb-05/stone.shtml   (795 words)

  
 Calculating Electronic Excited States
This is an introduction to the techniques used for the calculation of electronic excited states of molecules (sometimes called eximers).
Specifically, these are methods for obtaining wave functions for the excited states of a molecule from which energies and other molecular properties (such as dipole moments) can be calculated.
The easiest excited states to find using density functional theory techniques are those which are the lowest state of a given symmetry thus using a ground state calculation.
www.ccl.net /cca/documents/dyoung/topics-orig/excited.html   (1544 words)

  
 Stimulated Emission   (Site not responding. Last check: 2007-11-02)
If a bunch of electrons were put into an excited state somehow and then left to relax, the resulting radiation would be very spectrally limited (only one wavelength of light would be present) but the individual photons would not be in phase with one another.
If the atom is in the excited state, it may decay into the ground state by the process of spontaneous emission, releasing the difference in energies between the two states as a photon.
The rate of emission is thus proportional to the number of atoms in the excited state, N, and the density of the perturbing photons.
www.wikiverse.org /stimulated-emission   (830 words)

  
 CHP - Atomic Lifetimes and Linewidths   (Site not responding. Last check: 2007-11-02)
is the population in the excited state (j) and the A
is the linewidth in frequency units of a transition between an excited state and the ground state.
Since the ground state has an essentially infinite lifetime, the transition linewidth is governed by the width of the excited state.
www.chem.vt.edu /chem-ed/spec/atomic/theory/lifetime.html   (216 words)

  
 Olympus Microscopy Resource Center: Fluorescence - Jablonski Energy Diagram - Interactive Java Tutorial
Transitions between the states are illustrated as straight or wavy arrows, depending upon whether the transition is associated with absorption or emission of a photon (straight arrow) or results from a molecular internal conversion or non-radiative relaxation process (wavy arrows).
Transitions from the triplet excited state to the singlet ground state are forbidden, which results in rate constants for triplet emission that are several orders of magnitude lower than those for fluorescence.
The ground state oxygen molecule, which is normally a triplet, can be excited to a reactive singlet state, leading to reactions that bleach the fluorophore or exhibit a phototoxic effect on living cells.
www.olympusmicro.com /primer/java/jablonski/jabintro   (1562 words)

  
 Ground and Singlet Excited State Hydrogen-Bonding Interactions between 1-Azacarbazole and Amides
The above results show that, in the excited state, the equilibrium between the hydrogen bonded complexes and the free AC is not established during the life span of these species.
If this were the case, these species would be coupled in the excited state and, therefore, the fluorescence decays would be always biexponential, irrespective of the monitored emission wavelength.
Since such behavior was not observed, it is quite unlikely that free AC is the excited state precursor of the hydrogen-bonded complexes.
www.photobiology.com /photobiology2000/balon/index.htm   (2781 words)

  
 OSU Department of Chemistry Faculty Member
Femtosecond photophysics and photochemistry, ultrafast excited state dynamics, biophysical chemistry
Our results show that the lowest excited singlet states of the bases decay in hundreds of femtoseconds to vibrationally highly excited levels in the electronic ground state.
He was a postdoctoral scientist with Urs P. Wild at the ETH in Zurich from 1990 until 1992, and an Assistant Project Scientist from 1992 through 1995 in the group of Kent R. Wilson at the University of California, San Diego.
www.chemistry.ohio-state.edu /cgi/brochure?Faculty=Kohler   (591 words)

  
 Research
The surprisal, then, is a measure of the deviation of the measured final quantum state distribution from the predicted outcome of the unconstrained reaction (referred to as the prior expectation or prior distribution).
and Kr two-photon excited states in krypton and xenon buffer gases.
The kinetic profile for this laser-excited state was fit to a double exponential function to determine the slow and fast decay rates, and the collisional mixing was analyzed using a coupled two-state model.
www.ph.utexas.edu /~kohel/research.html   (829 words)

  
 EnergyLevelModel
When the stool is in its normal position the center of mass is higher than the ground state, so the gravitational potential energy of this excited energy state is higher than the ground state.
Notice that the center of mass of the stool is higher than the ground state, it is an excited state.
The change from the 2s to the 1s state is called a "forbidden transition." It does not occur in gasses in the laboratory.
isaac.exploratorium.edu /~pauld/activities/energylevelmodel/energylevelmodel.html   (1010 words)

  
 Alpha particle - Wikipedia, the free encyclopedia
They consist of two protons and two neutrons bound together into a particle identical to a helium nucleus; hence, it can be written as He Alpha particles are emitted by radioactive nuclei such as uranium or radium in a process known as alpha decay.
This sometimes leaves the nucleus in an excited state, with the emission of a gamma ray removing the excess energy.
In contrast to beta decay, alpha decay is mediated by the strong nuclear force.
en.wikipedia.org /wiki/Alpha_particle   (866 words)

  
 Spontaneous Emission   (Site not responding. Last check: 2007-11-02)
A simple model of spontaneous emission consists of an atom which may be in two electronic energy states, the ground state (1) and the excited state (2), with energies E
If the atom is in the excited state, it may spontaneously decay into the ground state, releasing the difference in energies between the two states as a photon.
Meta-stable states form a very important feature that is exploited in the construction of lasers.
www.wikiverse.org /spontaneous-emission   (621 words)

  
 Excited state first-order properties: *CCEXGR
Calculate all of the above-mentioned excited state properties (all the above-mentioned property integrals are needed).
Select which excited states the calculation of excited state properties are carried out for.
The default is all states according to the CCEXCI input section.
lacebark.ntu.edu.au /Dalton/node190.html   (307 words)

  
 Excited state   (Site not responding. Last check: 2007-11-02)
The lifetime (see resonance) of a system in an excited state is usually...
Once the electron is in its excited state, we deem the hydrogen atom to be in its...
When an atom is in an excited state, the electron can drop all the way to the...
www.serebella.com /encyclopedia/article-Excited_state.html   (1837 words)

  
 Excited state - InformationBlast   (Site not responding. Last check: 2007-11-02)
An excited state of an atom or nucleus possesses more energy than the ground state.
The lifetime of a molecule in an excited state is short.
Molecules return from an excited state by releasing energy.
www.informationblast.com /Excited_state.html   (51 words)

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