China
Africa
Explore chapters and articles related to this topic
Lasers for Spectroscopy
Published in Leon J. Radziemski, Richard W. Solarz, Jeffrey A. Paisner, Laser Spectroscopy and Its Applications, 2017
A molecule in an excited electronic state frequently has a different equilibrium position of its constituent nuclei than in the ground state, so that the minimum of the excited-state potential well is shifted with respect to the ground-state well, as shown in Fig. 2.1. The Franck- Condon principle requires that an electronic transition in a molecule must occur without a change in the position of the nuclei, so a molecule in a low vibrational level of the ground state which absorbs a photon must go to a high vibrational level of the excited electronic state S1. The high vibrational levels of the excited state relax to low vibrational levels in a picosecond or less in a typical dye molecule in solution, which is much faster than the S1 radiative lifetime of a few nanoseconds, so the fluorescence from S1 to the ground state comes from low vibrational levels. The shift in the potential wells requires that the fluorescence terminate on a high vibrational level of the ground state, and this vibration also quenches in less than a picosecond. This arrangement of pump, fluorescence, and fast relaxation processes is exactly that required for the four-level laser oscillator discussed in standard texts [Yariv, 1971; Siegman, 1971; Svelto, 1982; Tarasov, 1983]. The fluorescent emission is at longer wavelength or smaller photon energy than the pump. The shift between the peaks of the absorption and fluorescence spectra has been named the Stokes shift in honor of an early investigator of fluorescence.
Interfacial Kinetics and Hopping Transitions
Published in Juan Bisquert, The Physics of Solar Energy Conversion, 2020
The Franck–Condon principle states that the electronic quantum transition is so fast that the nuclear degrees of freedom of the molecule and its surrounding can be considered immobile during the transition of the electron. If the energies of the donor and the acceptor states are very different, the jump of the electron may occur assisted by a photon, as shown in Figure 5.7. In a molecular or polar system, the jump corresponds to a vertical transition that occurs in the configuration of the ground state of the system, as will be discussed further later. Then, the molecular system has to rearrange to achieve the equilibrium configuration of the excited state.
Symbols, Terminology, and Nomenclature
Published in W. M. Haynes, David R. Lide, Thomas J. Bruno, CRC Handbook of Chemistry and Physics, 2016
W. M. Haynes, David R. Lide, Thomas J. Bruno
Force constants (f, k)* - In molecular vibrations, the coefficients in the expression of the potential energy in terms of atom displacements from their equilibrium positions. In a diatomic molecule, f = d2V/dr2, where V(r) is the potential energy and r is the interatomic distance. [2] Fourier number (Fo) - A dimensionless quantity used in fluid mechanics, defined by Fo = at/l2, where a is thermal diffusivity, t is time, and l is length. [2] Fourier transform infrared spectroscopy (FTIR) - A technique for obtaining an infrared spectrum by use of an interferometer in which the path length of one of the beams is varied. A Fourier transformation of the resulting interferogram yields the actual spectrum. The technique is also used for NMR and other types of spectroscopy. Fractals - Geometrical objects that are self-similar under a change of scale; i.e., they appear similar at all levels of magnification. They can be considered to have fractional dimensionality. Examples occur in diverse fields such as geography (rivers and shorelines), biology (trees), and solid state physics (amorphous materials). Franck-Condon principle - An important principle in molecular spectroscopy which states that the nuclei in a molecule remain essentially stationary while an electronic transition is taking place. The physical interpretation rests on the fact that the electrons move much more rapidly than the nuclei because of their much smaller mass. Franklin (Fr) - Name sometimes given to the unit of charge in the esu system. Fraunhofer diffraction - Diffraction of light in situations where the source and observation point are so far removed that the wave surfaces may be considered planar. Fraunhofer lines - Sharp absorption lines in the spectrum of sunlight, caused by absorption of the solar blackbody radiation by atoms near the sun's surface. Free radical - See Radicals. The term "free radical" is often used more broadly for molecules that have a paramagnetic ground state (e.g., O2) and sometimes for any transient or highly reactive molecular species. Freezing point - See Melting point. Frequency ()* - Number of cycles of a periodic phenomenon divided by time. [1] Fresnel diffraction - Diffraction of light in a situation where the source and observation point are sufficiently close together that the curvature of the wave surfaces must be taken into account. Froude number (Fr) - A dimensionless quantity used in fluid mechanics, defined by Fr = v/(lg)1/2, where v is velocity, l is length, and g is acceleration due to gravity. [2] Fugacity (fB) - For a gas mixture, the fugacity of component B is defined as the absolute activity B times the limit, as the pressure p approaches zero at constant temperature, of pB/B. [2] Fullerenes - Compounds composed solely of an even number of carbon atoms, which form a cage-like fused-ring polycyclic system with twelve five-membered rings and the rest six-membered rings. The archetypal example is [60]fullerene, where the atoms and bonds delineate a truncated icosahedron. The term has been broadened to include any closed cage structure consisting entirely of three-coordinate carbon atoms. [5] Fulvalenes - The hydrocarbon fulvalene and its derivatives formed by substitution (and by extension, analogues formed
The feasibility of laser cooling: an investigation of ab initio of 88Sr35Cl including the hyperfine structure
Published in Molecular Physics, 2022
Quan-Shun Yang, Chao Song, Jingshuai Huang, Ming Fang, Mingjie Wan, Yanguang Yang
If the minimum values of the potential energy curves of the two electronic states are almost exactly one above the other, it produces a largeness transition probability of the vibration energy level (v' = 0 →v″ = 0) of the two electronic states, which satisfies the Franck-Condon principle. This coincides with the obtained FCFs, and it describes the overlap of the vibrational wave functions. The FCFs from the A2Π to X2Σ+ transition are obtained for the 88Sr35Cl molecule using the LEVEL8.0 program. The calculated data are listed in Table 6, and the corresponding graph is demonstrated in Figure 5. Table 6 obtained FCFs are highly diagonally distributed, as also indicated in Figure 5. Although FCFs of a high diagonal distribution are obtained, they do not represent everything for a laser cooling candidate molecule. In addition, it also need to satisfy the A2Π state with a short spontaneous emission lifetime, and this allows the laser cooling cycle to proceed quickly and produces a large spontaneous scattering force for laser cooling. The spontaneous radiative lifetimes at the nanosecond level are tabulated in Table 7 for v’ = 0–5 of the A2Π state.
Photoexcitation of brilliant cresyl blue dye in aqueous solution: TD-DFT study
Published in Molecular Physics, 2022
According to the Franck-Condon principle [26], the electronic transition from the ground state (GS) to the~excited state (ES) occurs at constant coordinates of the nuclei of the solute molecule, as well as the nuclei of the nearest solvation shell (vertical transition Evert in Figure 2). In this case, the molecule is in excited nonequilibrium (Franck-Condon, FC) state. This non-equilibrium nuclear core leads to the activation of vibrational energy levels (green wave in Figure 2). Since the latter obey the Boltzmann distribution, there are many transitions from different vibrational levels of the ground electronic state to different vibrational levels of the electronically excited state.