nonadiabatic transition
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2021 ◽  
Author(s):  
Ignacio Fernández Galván ◽  
Anders Brakestad ◽  
Morgane Vacher

Chemiexcitation, the generation of electronic excited states by a thermal reaction initiated on the ground state, is an essential step in chemiluminescence, and it is mediated by the presence of a conical intersection that allows a nonadiabatic transition from ground state to excited state. Conical intersections classified as sloped favor chemiexcitation over ground state relaxation. The chemiexcitation yield of 1,2-dioxetanes is known to increase upon methylation. In this work we explore to which extent this trend can be attributed to changes in the conical intersection topography or accessibility. Since conical intersections are not isolated points, but continuous seams, we locate regions of the conical intersection seams that are close to the configuration space traversed by the molecules as they react on the ground state. We find that conical intersections are energetically and geometrically accessible from the reaction trajectory, and that topographies favorable to chemiexcitation are found in all three molecules studied. Nevertheless, the results suggest that dynamic effects are more important for explaining the different yields than the static features of the potential energy surfaces.


2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Guang Yuan Zhu ◽  
Yi Qin ◽  
Miao Meng ◽  
Suman Mallick ◽  
Hang Gao ◽  
...  

AbstractThe semiclassical models of nonadiabatic transition were proposed first by Landau and Zener in 1932, and have been widely used in the study of electron transfer (ET); however, experimental demonstration of the Landau-Zener formula remains challenging to observe. Herein, employing the Hush-Marcus theory, thermal ET in mixed-valence complexes {[Mo2]-(ph)n-[Mo2]}+ (n = 1–3) has been investigated, spanning the nonadiabatic throughout the adiabatic limit, by analysis of the intervalence transition absorbances. Evidently, the Landau-Zener formula is valid in the adiabatic regime in a broader range of conditions than the theoretical limitation known as the narrow avoided-crossing. The intermediate system is identified with an overall transition probability (κel) of ∼0.5, which is contributed by the single and the first multiple passage. This study shows that in the intermediate regime, the ET kinetic results derived from the adiabatic and nonadiabatic formalisms are nearly identical, in accordance with the Landau-Zener model. The obtained insights help to understand and control the ET processes in biological and chemical systems.


2020 ◽  
Vol 3 (1) ◽  
Author(s):  
Hayato Goto ◽  
Taro Kanao

AbstractQuantum annealing, which is particularly useful for combinatorial optimization, becomes more powerful by using excited states, in addition to ground states. However, such excited-state quantum annealing is prone to errors due to dissipation. Here we propose excited-state quantum annealing started with the most stable state, i.e., vacuum states. This counterintuitive approach becomes possible by using effective energy eigenstates of driven quantum systems. To demonstrate this concept, we use a network of Kerr-nonlinear parametric oscillators, where we can start excited-state quantum annealing with the vacuum state of the network by appropriately setting initial detuning frequencies for the oscillators. By numerical simulations of four oscillators, we show that the present approach can solve some hard instances whose optimal solutions cannot be obtained by standard ground-state quantum annealing because of energy-gap closing. In this approach, a nonadiabatic transition at an energy-gap closing point is rather utilized. We also show that this approach is robust against errors due to dissipation, as expected, compared to quantum annealing started with physical excited (i.e., nonvacuum) states. These results open new possibilities for quantum computation and driven quantum systems.


2020 ◽  
Author(s):  
Guang Yuan Zhu ◽  
Yi Qin ◽  
Miao Meng ◽  
Suman Mallick ◽  
Hang Gao ◽  
...  

Abstract The semiclassical models of nonadiabatic transition were proposed first by Landau and Zener in 1932, which has been widely used in study of electron transfer (ET); however, experimental substantiation of the Landau-Zener formula remains challenging. Herein, employing the Marcus-Hush theory, thermal ET in mixed-valence complexes { [Mo2]-(ph)n-[Mo2] }+ (n = 1-3) is investigated and the Landau-Zener analysis performed in the adiabatic and nonadiabatic limits. Evidently, the Landau-Zener formula is valid in the adiabatic regime in a broader range of conditions than the theoretical limitation known as the narrow avoided-crossing. The intermediate system is identified with an overall transition probability (𝛋el) of ~ 0.5, which is resolved by the contributions from the single and the first multiple passage. The results unify the contemporary ET theories under the semiclassical framework. The obtained insights help to understand and control the ET processes in biological and chemical systems.


2020 ◽  
Author(s):  
Andrew Pohlman ◽  
Danil Kaliakin ◽  
Sergey Varganov ◽  
Sean Casey

<div>An understanding of the role that spin states play in semiconductor surface chemical reactions is currently limited. Herein, we provide evidence of a nonadiabatic reaction involving a localized singlet to triplet thermal excitation of the Si(100) surface dimer dangling bond. By comparing the β-hydrogen elimination kinetics of ethyl adsorbates probed by thermal desorption experiments to electronic structure calculation results, we determined that a coverage-dependent change in mechanism occurs. At low coverage, a nonadiabatic, inter-dimer mechanism is dominant, while adiabatic mechanisms become dominant at higher coverage. Computational results indicate that the spin flip is rapid near room temperature and the nonadiabatic path is accelerated by a barrier that is 40 kJ/mol less than the adiabatic path. Simulated thermal desorption reactions using nonadiabatic transition state theory (NA-TST) for the surface dimer electron spin flip are in close agreement with experimental observations.</div>


2020 ◽  
Author(s):  
Andrew Pohlman ◽  
Danil Kaliakin ◽  
Sergey Varganov ◽  
Sean Casey

<div>An understanding of the role that spin states play in semiconductor surface chemical reactions is currently limited. Herein, we provide evidence of a nonadiabatic reaction involving a localized singlet to triplet thermal excitation of the Si(100) surface dimer dangling bond. By comparing the β-hydrogen elimination kinetics of ethyl adsorbates probed by thermal desorption experiments to electronic structure calculation results, we determined that a coverage-dependent change in mechanism occurs. At low coverage, a nonadiabatic, inter-dimer mechanism is dominant, while adiabatic mechanisms become dominant at higher coverage. Computational results indicate that the spin flip is rapid near room temperature and the nonadiabatic path is accelerated by a barrier that is 40 kJ/mol less than the adiabatic path. Simulated thermal desorption reactions using nonadiabatic transition state theory (NA-TST) for the surface dimer electron spin flip are in close agreement with experimental observations.</div>


Molecules ◽  
2020 ◽  
Vol 25 (4) ◽  
pp. 882 ◽  
Author(s):  
Toshiyuki Takayanagi ◽  
Yuya Watabe ◽  
Takaaki Miyazaki

Many chemical reactions of transition metal compounds involve a change in spin state via spin inversion, which is induced by relativistic spin-orbit coupling. In this work, we theoretically study the efficiency of a typical spin-inversion reaction, 3Fe(CO)4 + H2 → 1FeH2(CO)4. Structural and vibrational information on the spin-inversion point, obtained through the spin-coupled Hamiltonian approach, is used to construct three degree-of-freedom potential energy surfaces and to obtain singlet-triplet spin-orbit couplings. Using the developed spin-diabatic potential energy surfaces in reduced dimensions, we perform quantum nonadiabatic transition state wave packet calculations to obtain the cumulative reaction probability. The calculated cumulative reaction probability is found to be significantly larger than that estimated from the one-dimensional surface-hopping probability. This indicates the importance of both multidimensional and nuclear quantum effects in spin inversion for polyatomic chemical reaction systems.


2020 ◽  
Vol 22 (10) ◽  
pp. 5500-5508 ◽  
Author(s):  
Aleksandr O. Lykhin ◽  
Sergey A. Varganov

The nonadiabatic transition state theory provides insight into the T1 → S0 intersystem crossing in thiophosgene driven by quantum tunneling through the barrier formed by the crossing T1 and S0 electronic states.


2020 ◽  
Vol 11 (26) ◽  
pp. 6856-6861
Author(s):  
Heesung Lee ◽  
So-Yeon Kim ◽  
Sang Kyu Kim

Multidimensional conical intersection seam has been characterized by utilizing the dynamic resonances in the nonadiabatic transition probability experimentally observed in the predissociation of thioanisole isotopomers.


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