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Introduction to Phosphors, Rare Earths, Properties and Applications
Published in Vijay B. Pawade, Sanjay J. Dhoble, Phosphors for Energy Saving and Conversion Technology, 2018
Vijay B. Pawade, Sanjay J. Dhoble
Forbidden transitions are observed due to the fact that the interaction of rare earth ions with the crystal field or with the lattice vibrations can mix states of different parties into the 4f states. Although these mixed states make the transitions observable, their oscillator strengths remain relatively low (forced electric dipole transitions). f-f transitions of rare earth ions can be allowed when mixing of opposite parity configurations of the 4f5d state occurs due to the presence of odd parity crystal fields. In the second order, the electric dipole transition becomes parity allowed. The transitions corresponding to the even values of J (0→0 excluded) increase in their oscillator strengths due to this effect. Transitions that are not allowed as an electric dipole may take place as a magnetic dipole. Therefore, magnetic dipole transitions obey the selection rules, as ∆L = 0, ∆S = 0, ∆l = 0, and ∆J = 0 (0→0 excluded). The selection rule on ∆L and ∆S becomes weak due to spin-orbit coupling. Interaction of rare earth ions with lattice vibrations can mix the state of different parties into 4f states. Vibronic transitions of RE ions are observed due to the coupling of 4fn state with a vibrational mode of the lattice, whereas in the first order, the coupling occurs only with IR vibrations to break the parity selection rule of the purely electronic f→f transitions.
Vibrational Spectroscopy and the Hydrogen Bond
Published in Michael M. Coleman, John F. Graf, Paul C. Painter, Specific Interactions and the Miscibility of Polymer Blends, 2017
Michael M. Coleman, John F. Graf, Paul C. Painter
We have briefly discussed one basic and inherent condition for infrared absorption, namely that the frequency of the absorbed radiation must correspond to the frequency of a normal mode of vibration and hence a transition between vibrational energy levels. This condition is not by itself sufficient. There are additional so-called selection rules that determine activity. Naturally, an understanding of the selection rules can only be attained through the methods or theories capable of successfully describing the interaction of radiation with matter, i.e. quantum mechanics. It is easier to obtain a mental picture of these interactions by first considering the classical interpretation, however, and this will be given briefly here. The quantum mechanical description will then be simply stated and the results compared.
Raman gas spectroscopy
Published in P. Dakin John, G. W. Brown Robert, Handbook of Optoelectronics, 2017
Andreas Knebl, Jürgen Popp, Torsten Frosch
Quantum mechanical selection rules govern the transitions. The occurring bands and branches and their spectral positions are the characteristics for the scattering molecule. Thus, the molecule can be unambiguously identified taking advantage of this spectral “fingerprint.” The scattering is basically independent of the initial laser wavelength (disregarding resonance effects). Hence, all gas species can be identified using one light source. The determination of allowed and active transitions, energy levels, and resulting Raman frequencies quickly becomes complicated, according to the complexity of the molecule. That is why the following theoretical consideration only covers linear molecules to point out the important principles and essential features.
A simplified Bixon–Jortner–Plotnikov method for fast calculation of radiationless transfer rates in symmetric molecules
Published in Molecular Physics, 2023
A. I. Martynov, A. S. Belov, V. K. Nevolin
The effect of symmetry also was taken into account and formulated as selection rules for transitions. If the rigid molecule makes the non-totally symmetric transfer, the internal conversion proceeds only via the Franck-Condon mechanism, but the contribution of the Herzberg-Teller effect is zero. The promoting modes belong only to one symmetry representation, the same as the transition itself. In terms of vibrational level numbers, the transitions can only be (provided that the initial state is 0), while other transitions are forbidden. The rest non-totally symmetric transitions can be only . The totally-symmetric modes are not restricted by selection rules and play the role of a surrounding for promoting modes. This manifold of transitions can be approximated by the Pekarian function. If the transfer is totally-symmetric or a molecule is non-symmetric, the Herzberg-Teller terms are non-zero. In the case of totally-symmetric transfer in a symmetric molecule, the promoting modes are totally symmetric. In the case of an asymmetric molecule, all modes take a part in the process. In both latter cases, there are no selection rules for promoting modes.
Calculation of the singlet-triplet magnetic and electro-quadrupole transitions intensity for Ge2 molecule
Published in Molecular Physics, 2022
Lidan Xiao, Jianlei Xue, Yong Liu, Bing Yan, B. F. Minaev
Electro-quadrupole and dipole transitions have different selection rules. Same as magnetic dipole or quadrupole radiation, only the g-g and u-u transitions are allowed, while the g-u transitions are forbidden. Thus, the quadrupole-induced a1Δg-transition {1} in Figure 2 could be useful in the Ge2 LIF spectra analysis.
The Impact of Interrupting Nurses on Mental Workload in Emergency Departments
Published in International Journal of Human–Computer Interaction, 2019
Jung Hyup Kim, Nithin Parameshwara, Wenbin Guo, Kalyan S. Pasupathy
To measure the mental workload, we developed an NGOMSL model. NGOMSL is a language form of the GOMS model, which is precisely constructed in a structured way (Kieras, 1988). It has been used as a cognitive modeling technique to support the description and prediction of human behaviors in complex systems (Fuller, 2010; Gil & Kaber, 2012). According to several case studies done by Zhang and Walji (2011), the GOMS approach is one of the best ways to analyze tasks related to electronic health record systems and to evaluate time on the tasks (mental or physical). In the field of human-computer interaction, this is one of the most popular methods for cognitive process evaluation (Saleem et al., 2009). The key components of NGOMSL model are defined as follows (John & Kieras, 1996): Goals: Goals are what a user needs to accomplish. The goals can be broken down into various levels of subgoals. To achieve the user’s general goal, all of the subgoals must be accomplished.Operators: Operators are the perceptual, cognitive, or motor actions used to complete the subgoals. They should represent the user’s mental or physical state. Each operator requires a particular execution time, which is assumed to be independent of its context.Methods: Methods are the procedures or sequences of operators needed to accomplish a goal. Each method shows how to achieve a single goal. The contents of the methods depend on a fixed combination of operators.Selection Rules: Selection rules specify the conditions for the methods to be used if more than one method is applicable. The user’s experience and knowledge of methods significantly influence the design of selection rules. They are usually formed as conditional statements.