| 1. |
- Banerjee, Ambar, et al.
(författare)
-
Photoinduced bond oscillations in ironpentacarbonyl give delayed synchronous bursts of carbonmonoxide release
- 2022
-
Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 13:1
-
Tidskriftsartikel (refereegranskat)abstract
- Early excited state dynamics in the photodissociation of transition metal carbonyls determines the chemical nature of short-lived catalytically active reaction intermediates. However, time-resolved experiments have not yet revealed mechanistic details in the sub-picosecond regime. Hence, in this study the photoexcitation of ironpentacarbonyl Fe(CO)5 is simulated with semi-classical excited state molecular dynamics. We find that the bright metal-to-ligand charge-transfer (MLCT) transition induces synchronous Fe-C oscillations in the trigonal bipyramidal complex leading to periodically reoccurring release of predominantly axial CO. Metaphorically the photoactivated Fe(CO)5 acts as a CO geyser, as a result of dynamics in the potential energy landscape of the axial Fe-C distances and non-adiabatic transitions between manifolds of bound MLCT and dissociative metal-centered (MC) excited states. The predominant release of axial CO ligands and delayed release of equatorial CO ligands are explained in a unified mechanism based on the σ*(Fe-C) anti-bonding character of the receiving orbital in the dissociative MC states.
|
|
| 2. |
- Berkowicz, Sharon, 1994-, et al.
(författare)
-
Unveiling the Structure and Thermodynamics of Deeply Supercooled Glycerol-Water Microdroplets with Ultrafast X-ray Scattering
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The liquid-liquid critical point (LLCP) hypothesis of water suggests that water exists in two structurally distinct liquid states, high- and low-density liquid (HDL, LDL), with an LLCP hidden in the supercooled regime at elevated pressures. However, its consequences for solvation and structural dynamics in aqueous solutions remain to be explored. Here, we probe the structure and thermodynamics of deeply supercooled microdroplets of prototypical aqueous solutions of glycerol. The combination of rapid evaporative cooling with ultrafast small- and wide-angle X-ray scatter-ing (SAXS, WAXS) allows us to outrun crystallization and gain access to the largely unexplored deeply supercooled dilute regime (3.2 mol% glycerol) down to T ≈ 229 K, which is not accessible by conventional cooling methods. The experimental results, and complementary molecular dynamics(MD) simulations, indicate an increase in the tetrahedral coordination and enhancement of HDL-and LDL-like density fluctuations upon supercooling. In addition, the extended temperature range of the MD simulations reveals a maximum in the isothermal compressibility at T ≈ 220 K, indicating the location of a Widom line shifted to slightly lower temperatures compared to that of pure water. We conclude that the apparent effect of the presence of glycerol molecules on the water hydrogen-bond structure resembles that of pressure. This opens the possibility to search for the existence of an LLCP in these aqueous solutions simply by varying the solute concentration.
|
|
| 3. |
- Borges, Lucas, 1996-, et al.
(författare)
-
Extending the Tavis-Cummings model for molecular ensembles : Exploring the effects of dipole self energies and static dipole moments
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Strong coupling of organic molecules to the vacuum field of a nanoscale cavity can be used to modify their chemical and physical properties. We extend the Tavis-Cummings model for molecular ensembles and show that the often neglected interaction terms arising from the static dipole moment and the dipole self-energy are essential for a correct description of the light-matter interaction in polaritonic chemistry. On the basis of a full quantum description, we simulate the excited-state dynamics and spectroscopy of MgH+molecules resonantly coupled to an optical cavity. We show that the inclusion of static dipole moments and the dipole self-energy is necessary to obtain a consistent model. We construct an efficient two-level system approach that reproduces the main features of the real molecular system and may be used to simulate larger molecular ensembles.
|
|
| 4. |
- C. Couto, Rafael, et al.
(författare)
-
Suppressing non-radiative decay of photochromic organic molecular systems in the strong coupling regime
- 2022
-
Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 24:32, s. 19199-19208
-
Tidskriftsartikel (refereegranskat)abstract
- The lifetimes of electronic excited states have a strong influence on the efficiency of organic solar cells. However, in some molecular systems a given excited state lifetime is reduced due to the non-radiative decay through conical intersections. Several strategies may be used to suppress this decay channel. The use of the strong light-matter coupling provided in optical nano-cavities is the focus of this paper. Here, we consider the meso–tert-butyl-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene molecule (meso–tert-butyl-BODIPY) as a showcase of how strong and ultrastrong coupling might help in the development of organic solar cells. The meso–tert-butyl-BODIPY is known for its low fluorescence yield caused by the non-radiative decay through a conical intersection. However, we show here that, by considering this system within a cavity, the strong coupling can lead to significant changes in the multidimensional landscape of the potential energy surfaces of meso–tert-butyl-BODIPY, suppressing almost completely the decay of the excited state wave packet back to the ground state. By means of multi configuration electronic structure calculations and nuclear wave packet dynamics, the coupling with the cavity is analyzed in-depth to provide further insight of the interaction. By fine-tuning the cavity field strength and resonance frequency, we show that one can change the nuclear dynamics in the excited state, and control the non-radiative decay. This may lead to a faster and more efficient population transfer or the suppression of it.
|
|
| 5. |
- Cho, Daeheum, et al.
(författare)
-
Imaging of transition charge densities involving carbon core excitations by all X-ray sum-frequency generation
- 2019
-
Ingår i: Philosophical Transactions. Series A. - : The Royal Society. - 1364-503X .- 1471-2962. ; 377:2145
-
Tidskriftsartikel (refereegranskat)abstract
- X-ray diffraction signals from the time-evolving molecular charge density induced by selective core excitation of chemically inequivalent carbon atoms are calculated. A narrowband X-ray pulse selectively excites the carbon K-edge of the –CH3 or –CH2F groups in fluoroethane (CH3–CH2F). Each excitation creates a distinct core coherence which depends on the character of the electronic transition. Direct propagation of the reduced single-electron density matrix, using real-time time-dependent density functional theory, provides the time-evolving charge density following interactions with external fields. The interplay between partially filled valence molecular orbitals upon core excitation induces characteristic femtosecond charge migration which depends on the core–valence coherence, and is monitored by the sum-frequency generation diffraction signal.
|
|
| 6. |
- Coates, Michael R., 1994-
(författare)
-
Fundamental interactions in transition metal reactions
- 2024
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Transition metal complexes that participate in homogeneous reactions often perform the role of a catalyst, facilitating novel reaction pathways. When these complexes are pushed away from their equilibrium, the arrangement of the coordinating ligands around the metal center is perturbed and new reaction pathways are opened. By using a light-induced “trigger” to push the metal complex away from its equilibrium, this process can be initiated with precision. This thesis is concerned with the theoretical understanding of light-induced “triggered” reactions that generate transient, short-lived photoproducts in solution, capable of reacting with the surrounding solvent medium. A combination of theoretical and experimental tools are employed to give precise information about the formation and decay of these transient photoproducts.In an effort to understand the innate differences between a broad range of transition metal complexes, electron configurations of the metal and its coordinating ligands are a natural starting point. These distinct electronic structures define the physical structure of the transition metal complex and explain the reactivity or lack of reactivity of the transition metal complex. To describe these electronic structures, robust quantum chemistry methods are required. Coinciding with these methods is a theoretical framework that aims to simulate the evolution of molecules by means of a molecular dynamics simulation.The present work involves the study of ironpentacarbonyl or Fe(CO)5 which we use to explain the reactive landscape of a broad class of carbonyl coordinated transition metal complexes. The part of the thesis devoted to Fe(CO)5 is divided into distinct sections (i) the short-time (femtosecond-to-picosecond) gas-phase excited state molecular dynamics that produces the transient species, (ii) the long-time (picosecond-to-nanosecond) liquid-phase ground state molecular dynamics which describes the intermediates formed by the transient species and (iii) the experimental probes of the former sections. A final part of the thesis connects carbonyl containing metal complexes to another broad and detailed class of nitrosyl containing metal complexes.
|
|
| 7. |
- Csehi, András, et al.
(författare)
-
Quantum control with quantum light of molecular nonadiabaticity
- 2019
-
Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 100:5
-
Tidskriftsartikel (refereegranskat)abstract
- Coherent control experiments in molecules are often done with shaped laser fields. The electric field is described classically and control over the time evolution of the system is achieved by shaping the laser pulses in the time or frequency domain. Moving on from a classical to a quantum description of the light field allows one to engineer the quantum state of light to steer chemical processes. The quantum field description of the photon mode allows one to manipulate the light-matter interaction directly in phase space. In this paper we demonstrate the basic principle of coherent control with quantum light on the avoided crossing in lithium fluoride. Using a quantum description of light together with the nonadiabatic couplings and vibronic degrees of freedoms opens up alternative perspective on quantum control. We show the deviations from control with purely classical light field and how back-action of the light field becomes important in a few-photon regime.
|
|
| 8. |
- Csehi, András, et al.
(författare)
-
Ultrafast dynamics in the vicinity of quantum light-induced conical intersections
- 2019
-
Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 21
-
Tidskriftsartikel (refereegranskat)abstract
- Nonadiabatic effects appear due to avoided crossings or conical intersections (CIs) that are either intrinsic properties in field-free space or induced by a classical laser field in a molecule. It was demonstrated that avoided crossings in diatomics can also be created in an optical cavity. Here, the quantized radiation field mixes the nuclear and electronic degrees of freedom creating hybrid field-matter states called polaritons. In the present theoretical study we go further and create CIs in diatomics by means of a radiation field in the framework of cavity quantum electrodynamics. By treating all degrees of freedom, that is the rotational, vibrational, electronic and photonic degrees of freedom on an equal footing we can control the nonadiabatic quantum light-induced dynamics by means of CIs. First, the pronounced difference between the the quantum light-induced avoided crossing and the CI with respect to the nonadiabatic dynamics of the molecule is demonstrated. Second, we discuss the similarities and differences between the classical and the quantum field description of the light for the studied scenario.
|
|
| 9. |
- Davidsson, Eric, 1983-
(författare)
-
Ensembles and Open Quantum Systems in Polaritonic Chemistry
- 2023
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Optical cavities are structures where excitations in the electromagnetic field (photons of light) are confined and generally long-lived. The spatial confinement will enhance interactions with any matter systems in the cavity, such that the behaviour of a combined system is best understood in terms of polaritonic states; mixtures of excitations in both light and matter. This polaritonic regime provides a novel approach for the modification and control of chemical reactions, and a multitude of experimental advancements are beginning to realise this potential. There are however many challenges with creating useful theoretical models of the prominent quantum-mechanical behaviour in these systems, where model complexities regularly require numerical simulations.In this thesis, we especially engage with two challenges from the field: One is to model cavities that contain ensembles of matter systems that interact collectively with the confined light. Another is to implement models based on open quantum systems, which is a dominant framework to include environment interactions.With this work, we aim to deepen the understanding of the physics in these polaritonic chemistry systems. Our strategy is to isolate critical processes in order to study their significance and impact. In different contexts, this either allows us to identify potential obstacles to avoid or highlights opportunities to achieve desired experimental conditions and technological objectives.
|
|
| 10. |
- Davidsson, Eric, et al.
(författare)
-
Simulating photodissociation reactions in bad cavities with the Lindblad equation
- 2020
-
Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 153:23
-
Tidskriftsartikel (refereegranskat)abstract
- Optical cavities, e.g., as used in organic polariton experiments, often employ low finesse mirrors or plasmonic structures. The photon lifetime in these setups is comparable to the timescale of the nuclear dynamics governing the photochemistry. This highlights the need for including the effect of dissipation in the molecular simulations. In this study, we perform wave packet dynamics with the Lindblad master equation to study the effect of a finite photon lifetime on the dissociation of the MgH+ molecule model system. Photon lifetimes of several different orders of magnitude are considered to encompass an ample range of effects inherent to lossy cavities.
|
|
