scholarly journals Intramolecular Vibrational Relaxation in Electronically Excited States

1983 ◽  
Vol 2 (5-6) ◽  
pp. 253-269 ◽  
Author(s):  
R. Voltz ◽  
A. Boeglin ◽  
A. A. Villaeys ◽  
S. H. Lin
Keyword(s):  
Vibrational Relaxation ◽  
Memory Function ◽  
Coherent Motion ◽  
Zeroth Order ◽  
Mechanical Mixing ◽  
Time Resolved ◽  
Physical Conditions ◽  
Electronically Excited ◽  
Intramolecular Vibrational Relaxation

A density matrix approach for describing intramolecular dynamics, with special application to vibrational relaxation in excited electronic states, is presented. We derive the master equations governing intramolecular transfer of excitation energy between the states in a zeroth-order basis defined by considering the excitation and detection conditions in the time-resolved experiments. It is shown that, in this formalism, the memory function plays a central role. We note that the form of intramolecular memory is determined by the importance of quantum mechanical mixing of the zeroth-order states. A distinction is made between the subsystems of states with strong and weak mixing properties; while the former account for quasiperiodic character of coherent motion, the latter display a Markovian behavior. The physical conditions fixing the relative importance of quasiperiodic and statistical dynamics in individual systems are discussed. In the application to time resolved intramolecular vibrational relaxation, special consideration is given to the nature of the initially excited doorway states and the intermode couplings. The symmetry restrictions and the possible role of rotational motion in vibrational relaxation are also discussed, before considering the recent results obtained by Zewail et al. with anthracene in the first excited singlet state.

Vibrational relaxation dynamics of β-carotene and its derivatives with substituents on terminal rings in electronically excited states as studied by femtosecond time-resolved stimulated Raman spectroscopy in the near-IR region

2018 ◽  
Vol 20 (5) ◽  
pp. 3320-3327 ◽  
Author(s):  
Tomohisa Takaya ◽  
Masato Anan ◽  
Koichi Iwata
Keyword(s):  
Raman Spectroscopy ◽  
Excited States ◽  
Vibrational Relaxation ◽  
Relaxation Dynamics ◽  
Time Resolved ◽  
Near Ir ◽  
Electronically Excited ◽  
Carbonyl Substitution ◽  
Β Carotene ◽  
Stimulated Raman

Time-resolved near-IR stimulated Raman spectroscopy indicates acceleration of vibrational relaxation in carotenoids by carbonyl substitution on their peripheral rings.

The role of molecular flexibility in accelerating intramolecular vibrational relaxation

1994 ◽  
Vol 72 (3) ◽  
pp. 652-659 ◽  
Author(s):  
G.A. Bethardy ◽  
Xiaouang Wang ◽  
David S. Perry
Keyword(s):  
Vibrational Relaxation ◽  
Methyl Formate ◽  
Spectral Features ◽  
Intermediate Coupling ◽  
Flexible Molecules ◽  
Original Line ◽  
Line Positions ◽  
Intramolecular Vibrational Relaxation ◽  
Large Amplitude Motion

Evidence is presented to show that intramolecular vibrational relaxation (IVR) is faster in flexible molecules when the initially prepared vibration is close to the bond about which the large-amplitude motion occurs. In each of 1-pentyne, ethanol, and propargyl alcohol, IVR lifetimes are known for two different hydride stretches and in each molecule internal rotation connects gauche and trans conformers. In each case the vibration that is closer to the center of flexibility shows faster relaxation. This trend is supported by the available IVR lifetimes for other flexible molecules (hydrogen peroxide, 1-butene, n-butane, methyl formate, and propargyl amine) and for some "rigid" molecules (1-butyne, isobutane, propyne, trans-2-butene, and tert-butylacetylene). The lifetimes for the halogenated molecules, 2-fluoroethanol, 1,2-difluoroethane, trans-1-chloro-2-fluoroethane, and trifluoropropyne are all in the range expected for rigid molecules. An algorithm is presented for the consistent calculation of IVR lifetimes from discrete frequency-resolved spectra, which range from the sparse through intermediate coupling cases. Wherever possible, the reported lifetimes have been calculated (or recalculated) from the original line positions and intensities. The lifetimes may be compared directly to those deduced from homogeneously broadened spectral features with a Lorentzian contour.

Influence of Magnetic Fields on Solar Hydrodynamics: Experimental Results

1977 ◽  
Vol 36 ◽  
pp. 143-180 ◽  
Author(s):  
J.O. Stenflo
Keyword(s):  
Solar Activity ◽  
Energy Balance ◽  
Magnetic Fields ◽  
Solar Atmosphere ◽  
General Problem ◽  
Solar Rotation ◽  
Active Regions ◽  
Physical Conditions ◽  
Dynamic Phenomena

It is well-known that solar activity is basically caused by the Interaction of magnetic fields with convection and solar rotation, resulting in a great variety of dynamic phenomena, like flares, surges, sunspots, prominences, etc. Many conferences have been devoted to solar activity, including the role of magnetic fields. Similar attention has not been paid to the role of magnetic fields for the overall dynamics and energy balance of the solar atmosphere, related to the general problem of chromospheric and coronal heating. To penetrate this problem we have to focus our attention more on the physical conditions in the ‘quiet’ regions than on the conspicuous phenomena in active regions.

Preparing the Child for Productive Life

IJOHMN ◽  
2019 ◽  
Vol 5 (4) ◽  
pp. 16
Author(s):  
Stella Baindu Fortune Fortune
Keyword(s):  
Learner Control ◽  
Counseling Services ◽  
Guidance And Counseling ◽  
School Life ◽  
Productive Life ◽  
Know How ◽  
Physical Conditions ◽  
The Family ◽  
Genetic Endowment

The nature of children’s development is greatly influenced by the environmental conditions in which they are brought up. The amount of social stimulation which they receive is of particular importance, and even if physical conditions are adequate, an unstimulating environment which provides with little opportunity or need to experiment or solve problems will result in low level of achievement. Perhaps the most important aspect of the child’s social development is beyond the reach of the teacher. For the first very important aspect of the child’s development lies in the home. Genetic endowment and cultural level of the family, coupled with the actual physical conditions of the home will have decisive effect on the child’s development and will continue to influence him throughout his school life. These factors are inaccessible to be influenced by the teacher but it is as well for him to have them in mind in his dealings with pupils. In addition, he will need to know how he may most effectively change his pupils along the lives he considers to be the most appropriate. That is, he will seek out the most efficient ways of getting pupils learn for productive life in future. The topic under review will be approached from various fronts which include; The Sociological and Philosophical models; role of the school; Learners’ responsibility; role of the teacher; discipline and learner control; role of the parent; guidance and counseling services and conclusion.

scholarly journals Endogenous memory reactivation during sleep in humans is clocked by slow oscillation-spindle complexes

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Thomas Schreiner ◽  
Marit Petzka ◽  
Tobias Staudigl ◽  
Bernhard P. Staresina
Keyword(s):  
Memory Function ◽  
Nrem Sleep ◽  
Stimulus Category ◽  
Learning Material ◽  
Memory Reactivation ◽  
Eeg Recordings ◽  
Surface Eeg ◽  
Function Of Sleep ◽  
Prior Experiences

AbstractSleep is thought to support memory consolidation via reactivation of prior experiences, with particular electrophysiological sleep signatures (slow oscillations (SOs) and sleep spindles) gating the information flow between relevant brain areas. However, empirical evidence for a role of endogenous memory reactivation (i.e., without experimentally delivered memory cues) for consolidation in humans is lacking. Here, we devised a paradigm in which participants acquired associative memories before taking a nap. Multivariate decoding was then used to capture endogenous memory reactivation during non-rapid eye movement (NREM) sleep in surface EEG recordings. Our results reveal reactivation of learning material during SO-spindle complexes, with the precision of SO-spindle coupling predicting reactivation strength. Critically, reactivation strength (i.e. classifier evidence in favor of the previously studied stimulus category) in turn predicts the level of consolidation across participants. These results elucidate the memory function of sleep in humans and emphasize the importance of SOs and spindles in clocking endogenous consolidation processes.

scholarly journals Benefits under the Sea: The Role of Marine Compounds in Neurodegenerative Disorders

Marine Drugs ◽  
2021 ◽  
Vol 19 (1) ◽  
pp. 24
Author(s):  
Mariano Catanesi ◽  
Giulia Caioni ◽  
Vanessa Castelli ◽  
Elisabetta Benedetti ◽  
Michele d’Angelo ◽  
...  
Keyword(s):  
Oxidative Stress ◽  
Neurodegenerative Disorders ◽  
Extreme Temperature ◽  
Bioactive Molecules ◽  
Neuroprotective Effects ◽  
Physical Conditions ◽  
Adjuvant Therapies ◽  
Marine Habitats ◽  
Marine Compounds

Marine habitats offer a rich reservoir of new bioactive compounds with great pharmaceutical potential; the variety of these molecules is unique, and its production is favored by the chemical and physical conditions of the sea. It is known that marine organisms can synthesize bioactive molecules to survive from atypical environmental conditions, such as oxidative stress, photodynamic damage, and extreme temperature. Recent evidence proposed a beneficial role of these compounds for human health. In particular, xanthines, bryostatin, and 11-dehydrosinulariolide displayed encouraging neuroprotective effects in neurodegenerative disorders. This review will focus on the most promising marine drugs’ neuroprotective potential for neurodegenerative disorders, such as Parkinson’s and Alzheimer’s diseases. We will describe these marine compounds’ potential as adjuvant therapies for neurodegenerative diseases, based on their antioxidant, anti-inflammatory, and anti-apoptotic properties.

scholarly journals The role of spin in the degradation of organic photovoltaics

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Ivan Ramirez ◽  
Alberto Privitera ◽  
Safakath Karuthedath ◽  
Anna Jungbluth ◽  
Johannes Benduhn ◽  
...  
Keyword(s):  
Transient Absorption ◽  
Bulk Heterojunction ◽  
Critical Factor ◽  
Model Systems ◽  
Transient Absorption Spectroscopy ◽  
Triplet States ◽  
Paramagnetic Resonance ◽  
Time Resolved ◽  
A Charge

AbstractStability is now a critical factor in the commercialization of organic photovoltaic (OPV) devices. Both extrinsic stability to oxygen and water and intrinsic stability to light and heat in inert conditions must be achieved. Triplet states are known to be problematic in both cases, leading to singlet oxygen production or fullerene dimerization. The latter is thought to proceed from unquenched singlet excitons that have undergone intersystem crossing (ISC). Instead, we show that in bulk heterojunction (BHJ) solar cells the photo-degradation of C60 via photo-oligomerization occurs primarily via back-hole transfer (BHT) from a charge-transfer state to a C60 excited triplet state. We demonstrate this to be the principal pathway from a combination of steady-state optoelectronic measurements, time-resolved electron paramagnetic resonance, and temperature-dependent transient absorption spectroscopy on model systems. BHT is a much more serious concern than ISC because it cannot be mitigated by improved exciton quenching, obtained for example by a finer BHJ morphology. As BHT is not specific to fullerenes, our results suggest that the role of electron and hole back transfer in the degradation of BHJs should also be carefully considered when designing stable OPV devices.

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