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Faraday Discussions | Page 2

Yi Yang, Christopher J Johnson
Clusters of ammonia or amines and sulfuric acid are predicted to drive the formation of new particles from atmospheric trace gases, but the role of water in this process, or even the extent of hydration of the clusters, is not well known. We present vibrational spectra of exactly mass-selected clusters of ammonia or dimethylamine and sulfuric acid with zero to four water molecules bound. These hydrated clusters are synthesized by storing initially-dry clusters in an ion trap held at 180 K with a small partial pressure of water vapor...
April 29, 2019: Faraday Discussions
Jonathan Ryan Hunt, Cindy Tseng, Jahan M Dawlaty
Photobases are molecules with increased pKa in the excited state that can serve to transduce light energy into proton removal capability. They can be used to control chemical reactions using light, such as removing protons from a catalytic site in reactions that are rate-limited by proton transfer. We identify and explore several major challenges toward their practical applications. Two important challenges are the need for pre-association (or ground state hydrogen bonding) between the proton donor and the photobase, and the need for excited state solvation of the photogenerated products...
April 26, 2019: Faraday Discussions
Wook Lee, Spiridoula Matsika
Photoinduced charge transfer between neighboring bases plays an important role in DNA. One of its important effects is shown in its ability to affect the photochemical yields of the formation of cyclobutane pyrimidine dimer (CPD) products between adjacent pyrimidine bases. In this work we examine how the energies of charge transfer states depend on the sequences of oligonucleotides using a hybrid quantum and molecular mechanics (QM/MM) methodology combined with the algebraic diagrammatic construction through a second order electronic structure method for excited states...
April 26, 2019: Faraday Discussions
Daria Ruth Galimberti, Sana Bougueroua, Jérôme Mahé, Matteo Tommasini, Anouk M Rijs, Marie-Pierre Gaigeot
The combined approach of gas phase IR-UV ion dip spectroscopy experiments and DFT-based molecular dynamics simulations for theoretical spectroscopy reveals the 3D structures of (Ac-Phe-OMe)1,2 peptides using their far-IR/THz signatures. Both experimental and simulated IR spectra are well-resolved in the 100-800 cm-1 domain, allowing an unambiguous assignment of the conformers, that could not be achieved in other more congested spectral domains. We also present and make proofs-of-principles for our newly developed theoretical method for the assignment of (anharmonic) vibrational modes from MD simulations based on graph theory coupled to APT-weighted internal coordinates velocities DOS spectra...
April 26, 2019: Faraday Discussions
Michael Kellogg, Ali Akil, Daniel Sylvinson Muthiah Ravinson, Laura Estergreen, Stephen E Bradforth, Mark E Thompson
Symmetry breaking charge transfer (SBCT) is a process where a symmetrically disposed pair of identical chromophores forms a charge transfer excited state with the hole and electron on different chromophores, i.e. chr-chr + hν → chr+-chr-. Herein we explore this process in two dipyrrin-based bichromophoric systems. One of these bisdipyrrins involved a pair of BODIPY chromophores linked by a single bond at their meso-positions (compound 1) and the other involved two dipyrrin ligands coordinated in a tetrahedral geometry at the Zn2+ ion (compound 2)...
April 25, 2019: Faraday Discussions
Johannes Mahl, Stefan Neppl, Friedrich Roth, Mario Borgwardt, Catherine Saladrigas, Benjamin Toulson, Jason Cooper, Tahiyat Rahman, Hendrik Bluhm, Jinghua Guo, Wanli Yang, Nils Huse, Wolfgang Eberhardt, Oliver Gessner
Electronic and lattice contributions to picosecond time-resolved X-ray absorption spectra (trXAS) of CuO at the oxygen K-edge are analyzed by comparing trXAS spectra, recorded using excitation wavelengths of 355 nm and 532 nm, to steady-state, temperature-dependent XAS measurements. The trXAS spectra at pump-probe time-delays ≥150 ps are dominated by lattice heating effects. Insight into the temporal evolution of lattice temperature profiles on timescales up to 100s of nanoseconds after laser excitation are reported, on an absolute temperature scale, with a temporal sensitivity and a spatial selectivity on the order of 10s of picoseconds and 10s of nanometers, respectively, effectively establishing an "ultrafast thermometer"...
April 25, 2019: Faraday Discussions
Justin Lyle, Thomas-C Jagau, Richard Mabbs
Photoelectron angular distributions determined in small energy increments between 3.522 and 3.650 eV reveal distinctly different detachment mechanisms within the CuF2-(X 1Σ+g) → linear CuF2(X 2Σ+g) + e- band. Certain channels also display non-Franck-Condon behaviour, the action spectra of which reveal rich structure. The behaviour reflects excitation to an electronically unbound anion state (at the linear geometry). The effects of the intermediate state are observed in the detachment behaviour at photon energies down to the X 1Σ+g → X 2Σ+g threshold...
April 25, 2019: Faraday Discussions
Zachary K Goldsmith, Alexander V Soudackov, Sharon Hammes-Schiffer
Photoinduced proton-coupled electron transfer (PCET) plays a key role in a wide range of energy conversion processes, and understanding how to design systems to control the PCET rate constant is a significant challenge. Herein a theoretical formulation of PCET is utilized to identify the conditions under which photoinduced PCET may exhibit inverted region behavior. In the inverted region, the rate constant decreases as the driving force increases even though the reaction becomes more thermodynamically favorable...
April 24, 2019: Faraday Discussions
Akihiko Kudo, Shunya Yoshino, Taichi Tsuchiya, Yuhei Udagawa, Yukihiro Takahashi, Masaharu Yamaguchi, Ikue Ogasawara, Hiroe Matsumoto, Akihide Iwase
Various types of Z-scheme systems for water splitting under visible light irradiation were successfully developed by employing Rh- and Ir-doped metal oxide powdered materials with relatively narrow energy gaps (EG): BaTa2O6:Ir,La (EG: 1.9-2.0 eV), NaTaO3:Ir,La (EG: 2.1-2.3 eV), SrTiO3:Ir (EG: 1.6-1.8 eV), NaNbO3:Rh,Ba (EG: 2.5 eV) and TiO2:Rh,Sb (EG: 2.1 eV), with conventional SrTiO3:Rh (an H2-evolving photocatalyst) or BiVO4 (an O2-evolving photocatalyst), and suitable electron mediators. The Z-scheme systems were classified into three groups depending on the combination of H2- and O2-evolving photocatalysts and electron mediator...
April 24, 2019: Faraday Discussions
James N Bull, Jack T Buntine, Michael S Scholz, Eduardo Carrascosa, Linda Giacomozzi, Mark H Stockett, Evan J Bieske
Substituted naphthalene anions (deprotonated 2-naphthol and 6-hydroxy-2-naphthoic acid) are spectroscopically probed in a tandem drift tube ion mobility spectrometer (IMS). Target anions are selected according to their drift speed through nitrogen buffer gas in the first IMS stage before being exposed to a pulse of tunable light that induces either photodissociation or electron photodetachment, which is conveniently monitored by scavenging the detached electrons with trace SF6 in the buffer gas. The photodetachment action spectrum of the 2-naphtholate anion exhibits a band system spanning 380-460 nm with a prominent series of peaks spaced by 440 cm-1, commencing at 458...
April 24, 2019: Faraday Discussions
Shaunak M Shaikh, Arnab Chakraborty, James Alatis, Meng Cai, Evgeny Danilov, Amanda J Morris
We present the synthesis and photophysical characterization of a water stable PCN-223(freebase) metal organic framework (MOF) constructed from meso-tetrakis(4-carboxyphenyl)porphyrin (TCPP). The photophysical properties of the synthesized crystalline material were studied using a wide range of steady-state and time-resolved spectroscopic techniques. Quenching experiments performed on TCPP and PCN-223 demonstrated that the extent and the rate of quenching in the MOF is significantly higher than the monomeric ligand...
April 24, 2019: Faraday Discussions
Petr Dohnal, Dmytro Shapko, Ábel Kálosi, Miroslava Kassayová, Štěpán Roučka, Serhiy Rednyk, Radek Plašil, Michal Hejduk, Juraj Glosík
We present studies on the thermalisation of H3+ ions in a cold He/Ar/H2 plasma at temperatures 30-70 K. We show that we are able to generate a rotationally thermalised H3+ ensemble with a population of rotational and nuclear spin states corresponding to a particular ion translational temperature. By varying the para-H2 fraction used in the experiment we are able to produce para-H3+ ions with fractional populations higher than those corresponding to thermodynamic values. At 35 K, only the lowest rotational states of para and ortho H3+ are populated...
April 24, 2019: Faraday Discussions
Gareth W Richings, Christopher Robertson, Scott Habershon
The ground-up design of new molecular sunscreens, with improved photostability, absorbance and spectral coverage, stands as a challenge to fundamental chemical science. Correlating sunscreen molecular structure and function requires detailed insight into the relaxation pathways available following photoexcitation; however, the complex coupled electron/nuclear dynamics in these systems stands as a tough challenge to computational chemistry. To address this challenge, we have recently developed efficient and accurate simulation methods to model non-adiabatic dynamics of general molecular systems as a route to correlating photoinduced dynamics and potential sunscreen activity...
April 24, 2019: Faraday Discussions
Bo Xu, Tamar Stein, Utuq Ablikim, Ling Jiang, Josie Hendrix, Martin Head-Gordon, Musahid Ahmed
Polycyclic aromatic hydrocarbons (PAHs) may comprise up to 20% of the carbon budget in our galaxy and most PAHs condense onto water-rich icy grain mantles. Benzene-water clusters have been invoked as model systems for studying the photo-processing of water ice mantles containing PAHs. However, there is a paucity of information on larger aromatics, where the extended π cloud could affect photo-processing. In this study, tunable vacuum ultraviolet (VUV) photoionization of naphthalene-water clusters Nx(H2O)y (N denotes naphthalene) is performed using synchrotron radiation and analyzed by reflectron time-of-flight mass spectrometry...
April 24, 2019: Faraday Discussions
Jeremy J Baumberg
Hot electron photochemistry has made strong claims for improved control of chemical reactions. Here I discuss these claims in the light of a plethora of model experiments and theories, asking what are the key issues to solve. I particularly highlight the need to understand nanoscale thermal hot-spots, thermal gradients, and thermal transport, as well as the conventional optical confinement in plasmonics. I note how the 'direct electron transfer' process seems to dominate, and resembles well known 'indirect excitons' in semiconductor quantum wells...
April 24, 2019: Faraday Discussions
Shou-Ting Hsieh, Lu Zhang, De-Wei Ye, Xuhui Huang, Yuan-Chung Cheng
Here we present our theoretical investigations into the light reaction in the dimeric photosystem II (PSII) core complex. An effective model for excitation energy transfer (EET) and primary charge separation (CS) in the PSII core complex was developed, with model parameters constructed based on molecular dynamics (MD) simulation data. Compared to experimental results, we demonstrated that this model faithfully reproduces the absorption spectra of the RC and core light-harvesting complexes (CP43 and CP47) as well as the full EET dynamics among the chromophores in the PSII core complex...
April 24, 2019: Faraday Discussions
Jana Roithová, Juraj Jašík, Jesus J Del Pozo Mellado, Dieter Gerlich
The combination of cryogenic ion traps with suitable light sources and standard tools of mass spectrometry has led to many innovative applications in previous years. This paper presents the combination of our versatile instrument with a supercontinuum laser for the rapid identification of ions that might be of special interest, e.g. as candidates for diffuse interstellar bands carriers. Using a linear wire quadrupole ion trap at 3 K, routine He-tagging, long irradiation times, and the brilliance and wide spectral range of a crystal fiber laser, mass selected ions have been exposed to spectral fluencies larger than 10 mJ (nm cm2)-1...
April 24, 2019: Faraday Discussions
Anna Lishchuk, Cvetelin Vasilev, Matthew P Johnson, C Neil Hunter, Päivi Törmä, Graham J Leggett
When light-harvesting complex II (LHCII), isolated from spinach, is adsorbed onto arrays of gold nanostructures formed by interferometric lithography, a pronounced splitting of the plasmon band is observed that is attributable to strong coupling of the localised surface plasmon resonance to excitons in the pigment-protein complex. The system is modelled as coupled harmonic oscillators, yielding an exciton energy of 2.24 ± 0.02 eV. Analysis of dispersion curves yields a Rabi energy of 0.25 eV. Extinction spectra of the strongly coupled system yield a resonance at 1...
April 24, 2019: Faraday Discussions
Pavel Chábera, Lisa A Fredin, Kasper S Kjær, Nils W Rosemann, Linnea Lindh, Om Prakash, Yizhu Liu, Kenneth Wärnmark, Jens Uhlig, Villy Sundström, Arkady Yartsev, Petter Persson
Ultrafast dynamics of photoinduced charge transfer processes in light-harvesting systems based on Earth-abundant transition metal complexes are of current interest for the development of molecular devices for solar energy conversion applications. A combination of ultrafast spectroscopy and first principles quantum chemical calculations of a recently synthesized iron carbene complex is used to elucidate the ultrafast excited state evolution processes in these systems with particular emphasis on investigating the underlying reasons why these complexes show promise in terms of significantly extended lifetimes of charge transfer excited states...
April 24, 2019: Faraday Discussions
J A Gibbard, R E Continetti
Photoelectron-photofragment coincidence (PPC) spectroscopy is used to examine the dissociative photodetachment (DPD) of I3-. The high beam energy PPC spectrometer for complex anions couples an electrospray ionization source, a hexapole accumulation ion trap and a linear accelerator to produce fast beams of I3- (M = 381 amu) anions, the heaviest system studied to date. Following photodetachment, the photoelectron and up to three photofragments are recorded in coincidence yielding a kinematically complete picture of the DPD dynamics at beam energies of 11 keV and 21 keV...
April 23, 2019: Faraday Discussions
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