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We investigated the effect of electron correlation for three-electrons systems on the K-shell, KL(1S)-shells (singlet states), and KL(3S)-shells (triplet states) in the ground state of Li-like ions (Li atom, Be+ ion, B+2 ion, and C+3 ion). While studying about the properties of atoms, you will look at values of positions corresponding to the maximum values of one particle's radial function D(r). Approximation techniques such as Hartree-Fock (HF) and Configuration Interaction (CI) were also used to compute the inter particle distribution of functions f(r12) and the differences in positions values (Δr) and maximum values ΔD(r) for the inter-shells KL(1S)-shells (singlet states) and KL(3S) inter particle (r12). As the number of ionizations increases, so do the attraction potential energy and the repulsion potential energy ; however, there is a significant difference in this case, which applies to the energies values , < T >, and < E >. All computations in Mathematics 2015 were done in atomic units, and the attributes obtained via equations were programmed, finally, the obtained data were treated statistically using the statistical program SPSS version 20,to find out the extent of convergence or divergence in the results between the current work and the practical data. It is possible to benefit from the results obtained in predicting and interpreting electronic spectra, such as UV-Vis absorption spectra, is facilitated by Hartree-Fock calculations. These simulations assist in understanding experimental spectroscopic data. [ABSTRACT FROM AUTHOR]

Intermolecular interactions modulate the electro-optical properties of molecular materials and the nature of low-lying exciton states. Molecular materials composed by oligoacenes are extensively investigated for their semiconducting and optoelectronic properties. Here, we analyze the exciton states derived from time-dependent density functional theory (TDDFT) calculations for two oligoacene model aggregates: naphthalene and anthracene dimers. To unravel the role of inter-molecular interactions, a set of diabatic states is selected, chosen to coincide with local (LE) and charge-transfer (CT) excitations within a restricted orbital space including two occupied and two unoccupied orbitals for each molecular monomer. We study energy profiles and disentangle inter-state couplings to disclose the (CT) character of singlet and triplet exciton states and assess the influence of inter-molecular orientation by displacing one molecule with respect to the other along the longitudinal translation coordinate. The analysis shows that (CT) contributions are relevant, although comparably less effective for triplet excitons, and induce a non-negligible mixed character to the low-lying exciton states for eclipsed monomers and for small translational displacements. Such (CT) contributions govern the La/Lb state inversion occurring for the low-lying singlet exciton states of naphthalene dimer and contribute to the switch from H- to J-aggregate type of the strongly allowed Bb transition of both oligoacene aggregates. [ABSTRACT FROM AUTHOR]

A protocol to generate atomic singlet state of three atoms is proposed. The strong Rydberg interactions between atoms mediate the multi‐qubit operations and help to simplify the dynamics of the system. The effective Hamiltonian is constructed in the regime of Rydberg blockade and the evolution path is built up from an initial state to the target singlet state via the Lie‐transform‐based pulse design. Numerical simulations show the protocol can produce atomic singlet state with high fidelity and holds robustness against several types of experimental imperfections. Therefore, it may provide some useful results for the generation of singlet states in atomic system. [ABSTRACT FROM AUTHOR]

Solution-state distance restraints for protein structure determination with Ångström-level resolution rely on through-space transfer of magnetization between nuclear spins. Such magnetization transfers, named Overhauser effects, occur via dipolar magnetic couplings. We demonstrate improvements in magnetization transfer using long-lived coherences (LLCs)—singlet-triplet superpositions that are antisymmetric with respect to spin-permutation within pairs of coupled magnetic nuclei—as the magnetization source. Magnetization transfers in the presence of radio-frequency irradiation, known as ‘rotating-frame’ Overhauser effects (ROEs), are predicted by theory to improve by the use of LLCs; calculations are matched by preliminary experiments herein. The LLC-ROE transfers were compared to the transmission of magnetization via classical transverse routes. Long-lived coherences accumulate magnetization on an external third proton, K, with transfer rates that depended on the tumbling regime. I,S →K transfers in the LLC configuration for (I,S) are anticipated to match, and then overcome, the same transfer rates in the classical configuration as the molecular rotational correlation times increase. Experimentally, we measured the LLC-ROE transfer in dipeptide AlaGly between aliphatic protons in different residues K = Ala − Hα and (I,S) = Gly − Hα1,2 over a distance dK,I,S = 2.3 Å. Based on spin dynamics calculations, we anticipate that, for such distances, a superior transfer of magnetization occurs using LLC-ROE compared to classical ROE at correlation times above τC=10 ns. The LLC-ROE effect shows potential for improving structural studies of large proteins and offering constraints of increased precision for high-affinity protein-ligand complexes in slow tumbling in the liquid state.

Diazirine moieties are chemically stable and have been incorporated into biomolecules without impediment of biological activity. The 15N2 labeled diazirines are appealing motifs for hyperpolarization supporting relaxation protected states with long‐lived lifetimes. The (‐CH15N2) diazirine groups investigated here are analogues to methyl groups, which provides the opportunity to transfer polarization stored on a relaxation protected (‐CH15N2) moiety to 1H, thus combining the advantages of long lifetimes of 15N polarization with superior sensitivity of 1H detection. Despite the proximity of 1H to 15N nuclei in the diazirine moiety, 15N T1 times of up to (4.6±0.4) min and singlet lifetimes Ts of up to (17.5±3.8) min are observed. Furthermore, we found terminal diazirines to support hyperpolarized 1H2 singlet states in CH2 groups of chiral molecules. The singlet lifetime of 1H singlets is up to (9.2±1.8) min, thus exceeding 1H T1 relaxation time (at 8.45 T) by a factor of ≈100. [ABSTRACT FROM AUTHOR]

A new methodology for producing hyperpolarized 13 C nuclei in small organic systems via parahydrogen induced polarization (PHIP) is proposed: ADAPT (Alternating Delays Achieve Polarization Transfer). The theoretical foundation of the process is investigated in some detail and experimental examples demonstrating the viability of the approach are provided as well. The number of adjustable parameters is fewer than most of other conversion schemes. The achieved theoretical heteronuclear polarization is close to unity for any examined magnetic equivalence regime. The duration of the pulse sequence, which was successfully implemented, can be shorter than other established methods reducing possible relaxation losses. The conversion scheme is robust to B 1 inhomogeneities, but more sensitive to off-resonance RF irradiation. [ABSTRACT FROM AUTHOR]

We have demonstrated two radiofrequency pulse methods which convert the nuclear singlet order of proton spin pairs into the magnetisation of nearby 13 C nuclei. These irradiation schemes work well in the near-equivalence regime of the three-spin system, which applies when the difference in the two 1 H- 13 C couplings is much smaller than the 1 H- 1 H coupling. We use pulse sequences to generate thermally polarized singlet states in a reproducible manner, and study the singlet-to-magnetisation transfer step. Preliminary results demonstrate a parahydrogen-enhanced 13 C polarization level of at least 9%, providing a signal enhancement factor of more than 9000, using 50% enriched parahydrogen. [ABSTRACT FROM AUTHOR]

We describe here the development of time-correlated single-photon counting techniques from the early use of spark discharge lamps as light sources through to the use of femtosecond mode-locked lasers through the personal work of the author.We used laser-excited fluorescence in studies on energy migration and rotational relaxation in synthetic polymer solutions, in biological probe molecules and in supersonic jet expansions. Time-correlated single-photon counting was the first method used in early fluorescence lifetime imaging microscopy (FLIM), and we outline the development of this powerful technique, with a comparison of techniques including wide-field microscopy. We employed these modern forms of FLIM to study single biological cells, and applied FLIM also to gain an understanding the distribution in tissue, and fates of photosensitizer molecules used in photodynamic therapy. We also describe the uses and instrumental design of laser systems for the study of ultrafast time-resolved vibrational spectroscopy. [ABSTRACT FROM AUTHOR]

Nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) are supremely important techniques with numerous applications in almost all branches of science. However, until recently, NMR methodology was limited by the time constant T1 for the decay of nuclear spin magnetization through contact with the thermal molecular environment. Long-lived states, which are correlated quantum states of multiple nuclei, have decay time constants that may exceed T1 by large factors. Here we demonstrate a nuclear long-lived state comprising two 13C nuclei with a lifetime exceeding one hour in room-temperature solution, which is around 50 times longer than T1. This behavior is well-predicted by a combination of quantum theory, molecular dynamics, and quantum chemistry. Such ultra-long-lived states are expected to be useful for the transport and application of nuclear hyperpolarization, which leads to NMR and MRI signals enhanced by up to five orders of magnitude. [ABSTRACT FROM AUTHOR]

Based on quantum Zeno dynamics and adiabatic passage, a scheme for the generation of three-qutrit singlet states for three atoms distributed in three fiber-coupled cavities is proposed, which is insensitive to the fluctuation of atom-cavity coupling rate g and fiber-cavity coupling rate ν when ν ≥ g . Moreover, the influence of atomic spontaneous emission and photon loss on the fidelity is greatly reduced since there are no excitations for atoms, cavities, and fibers. [ABSTRACT FROM AUTHOR]

Some quantum cryptographic protocols can be implemented with specially prepared metaphorical chocolate balls representing local hidden variables, others protected by value indefiniteness cannot. This latter feature, which follows from Bell– and Kochen–Specker type arguments, is only present in systems with three or more mutually exclusive outcomes. Conversely, there exist local hidden variable models based on chocolate ball configurations utilizable for cryptography which cannot be realized by quantum systems. The possibility that quantum cryptography supported by value indefiniteness (contextuality) has practical advantages over more conventional quantum cryptographic protocols remains highly speculative. [ABSTRACT FROM AUTHOR]

The longitudinal nuclear relaxation time, T 1 , sets a stringent limit on the range of information that can be obtained from magnetic resonance imaging (MRI) experiments. Long-lived nuclear spin states provide a possibility to extend the timescale over which information can be encoded in magnetic resonance. We introduce a strategy to localize an ensemble of molecules for a significantly extended duration (∼30 times longer than T 1 in this example), using a spatially selective conversion between magnetization and long-lived singlet order. An application to tagging and transport is proposed. [ABSTRACT FROM AUTHOR]

Highlights: [•] Application of para-hydrogen polarized samples as molecular imaging agents and future challenges. [•] Detection of minute substance amounts for reactor monitoring and trace analysis. [•] Use of PHIP in inhomogeneous fields and in time domain experiments. [•] Recent developments of PHIP phenomena in ultra-low field and zero-field NMR. [ABSTRACT FROM AUTHOR]

Abstract: First direct and quantitative study of singlet states using density matrix tomography is reported. A robust scheme for the tomography of a general density matrix of two spin 1/2 nuclei is introduced for this purpose. The study is carried out at different spin-lock conditions and the results are compared. [ABSTRACT FROM AUTHOR]

In a recent paper [A. Ahanj et al., Phys. Lett. A368 (2007) 34], we gave a classical protocol to simulate quantum correlations corresponding to the spin-s singlet state for the infinite sequence of spins satisfying 2s + 1 = 2n. In the present paper, we have generalized this result by giving a classical protocols to exactly simulate quantum correlations implied by the spin-s singlet state corresponding to all integer as well as half-integer spin values s. The class of measurements we consider here are only those corresponding to spin observables, as has been done in the above-mentioned paper. The required amount of communication is found to be ⌈log2(s + 1)⌉ in the worst case scenario, where ⌈x⌉ is the least integer greater than or equal to x. [ABSTRACT FROM AUTHOR]

Abstract: The singlet, triplet and cationic manifolds of Cl2O have been studied by multi-reference multi-root configuration interaction calculations, with large basis sets which include Rydberg functions. Numerous electronically excited and ionic states were obtained, which provide the most comprehensive interpretation of the known absorption (energy range to ∼10eV) and the photoionization efficiency spectra (energy range 11–16eV). There is a good correlation between the observed Rydberg state energies and the present calculated ones, for a series of bands involving the 1st and 4th ionization energies. Little is known concerning Rydberg states for the 2nd and 3rd ionization energies. The separation of Rydberg states with same upper state but varying lower state, show systematic trends, which independently confirm the order of cationic states in the UV-PES spectrum as: 2B1 < 2B2 < 2A1 < 2A2 < 2B1 <9A1 < 2B2. The lowest electronic state found for this system is the unsymmetrical 3A″ (CS ) form, where the asymmetry allows a lower energy channel towards dissociation. At this level of theoretical study, the dissociation energy of Cl2O→Cl + OCl is 1.382eV. A series of low-lying singlet and triplet states with either C 2 V or D ∞ h symmetry were also determined; in the former, the bond angle in particularly variable with the electronic state. [Copyright &y& Elsevier]

Abstract: Long-lived spin states have been observed in a variety of systems. Although the dynamics underlying the long lifetimes of these states are well understood in the case of two-spin systems, the corresponding dynamics in systems containing more spins appear to be more complex. Recently it has been shown that a selection rule for transitions mediated by intramolecular dipolar relaxation may play a role in determining the lifetimes of long-lived states in systems containing arbitrary numbers of spins. Here we present a theory of long-lived states in systems containing three and four spins and demonstrate how it can be used to identify states that have little or no intramolecular dipolar relaxation. [Copyright &y& Elsevier]

Abstract: Pulsed Field Gradients (PFGs) have become ubiquitous tools not only for Magnetic Resonance Imaging (MRI), but also for NMR experiments designed to study translational diffusion, for spatial encoding in ultra-fast spectroscopy, for the selection of desirable coherence transfer pathways, for the suppression of solvent signals, and for the elimination of zero-quantum coherences. Some of these experiments can only be carried out if three orthogonal gradients are available, while others can also be implemented using a single gradient, albeit at some expense of performance. This paper discusses some of the advantages of triple- with respect to single-gradient probes. By way of examples we discuss (i) the measurement of small diffusion coefficients making use of the long spin-lattice relaxation times of nuclei with low gyromagnetic ratios γ such as nitrogen-15, and (ii) the elimination of zero-quantum coherences in Exchange or Nuclear Overhauser Spectroscopy (EXSY or NOESY) experiments, as well as in methods relying on long-lived (singlet) states to study very slow exchange or diffusion processes. [Copyright &y& Elsevier]

Abstract: The 1,2,5-thiadiazole VUV absorption spectrum over the range 5–12eV has been obtained for the first time. It shows broad bands centred near 5.0, 7.2, 7.7, 8.7, 9.6 and 10.6eV; several of these show well resolved vibrational structure. A number of valence states and Rydberg states relating to the first and second ionisation energies have been identified. The doubling of some bands in the 4.7eV region (previously reported) is confirmed; a 3s Rydberg state shows a similar phenomenon, which we also attribute to a non-planar upper state; a study of the (planar) equilibrium geometry of the corresponding triplet Rydberg state shows it is a saddle point. Electronic excitation energies for valence (singlet and triplet) and Rydberg-type states have been computed using ab initio multi-reference multi-root CI methods. These studies used a triple-zeta+double polarisation basis set, augmented by diffuse (Rydberg) orbitals. The theoretical study shows the nature of the more intense Rydberg state types, and positions of the main valence and Rydberg bands. There is generally a good correlation between the theoretical intensities and the experimental envelope. Reconsideration of the order of cationic states in the UV-photoelectron spectrum, crucial to the Rydberg state interpretation, has led to the sequence: 2B1 < 2B2 < 2A2 < 2A1. Study of the excitation energies to specific upper states, also supports this order. The value of IE1 is refined to 10.111eV. Equilibrium structures show the π- and σ-cations are planar, in contrast to the lowest triplet state. [Copyright &y& Elsevier]

Abstract: A technique is described for filtering out the components of an NMR signal that have passed through an isotropic spin order term. The method involves a coordinated cycle of three radiofrequency phase angles, where two of the phases correspond to the polar angles describing the vertices of a regular polyhedron, and the third angle is stepped around a circle. The most economical isotropic filtering scheme involves a 12-step phase cycle based on tetrahedral symmetry. The method is used to filter out NMR signals that have passed through singlet populations in a solution NMR experiment. [Copyright &y& Elsevier]

Abstract: Long-lived singlet states have been observed in the solution NMR of spin systems containing more than two coupled spins, despite the fact that the singlet state is expected to be quenched by small long-range J-couplings. We show that the stability of localized singlet states may be explained by taking into account the intra-pair J-coupling between the two spins which participate in the singlet state. The relatively strong intra-pair J-coupling protects the singlet state against quenching by weaker out-of-pair J-couplings. [Copyright &y& Elsevier]

Abstract: The existence of long-lived nuclear spin states in four-spin systems is explored by solution-state NMR experiments. Long-lived states are proved to exist in three different natural product molecules, each containing either a AA′BB′ or a AA′XX′ proton spin system. The measured state lifetimes are between four and eight times the spin–lattice relaxation time constants. [Copyright &y& Elsevier]

Abstract: Early assignments of the vacuum UV photoabsorption spectrum of allene (1951–1972) gave a number of Rydberg series, but these series had limiting values for the ionization potential, which are incompatible (by up to 0.4eV) with adiabatic IPs from molecular beam and photoelectron spectra (UV-PES). Following our recent re-analysis of the VUV spectrum of allene by systematic overlay of the VUV and UV-PES spectra, a number of new experimental assignments were obtained; specifically the following assignments provide a target for this theoretical study: 3s, 6.180; 3p, 6.960; 3d, 7.910; 4s, 8.076eV. We now use multi-root configuration interaction calculations to determine the theoretical envelopes of both valence and Rydberg states. The CI calculations give a consistent picture of the Rydberg assignments as well as giving a clear indication of the positions of valence states. The second moment expectation values and oscillator strengths are used to determine the nature of the electronic states observed experimentally. [Copyright &y& Elsevier]

Solution-state distance restraints for protein structure determination with Ångström-level resolution rely on through-space transfer of magnetization between nuclear spins. Such magnetization transfers, named Overhauser effects, occur via dipolar magnetic couplings. We demonstrate improvements in magnetization transfer using long-lived coherences (LLCs)—singlet-triplet superpositions that are antisymmetric with respect to spin-permutation within pairs of coupled magnetic nuclei—as the magnetization source. Magnetization transfers in the presence of radio-frequency irradiation, known as 'rotating-frame' Overhauser effects (ROEs), are predicted by theory to improve by the use of LLCs; calculations are matched by preliminary experiments herein. The LLC-ROE transfers were compared to the transmission of magnetization via classical transverse routes. Long-lived coherences accumulate magnetization on an external third proton, K, with transfer rates that depended on the tumbling regime. I , S   → K transfers in the LLC configuration for (I,S) are anticipated to match, and then overcome, the same transfer rates in the classical configuration as the molecular rotational correlation times increase. Experimentally, we measured the LLC-ROE transfer in dipeptide AlaGly between aliphatic protons in different residues K = Ala − Hα and (I,S) = Gly − Hα1,2 over a distance d K , I , S = 2.3 Å. Based on spin dynamics calculations, we anticipate that, for such distances, a superior transfer of magnetization occurs using LLC-ROE compared to classical ROE at correlation times above τ C = 10   n s . The LLC-ROE effect shows potential for improving structural studies of large proteins and offering constraints of increased precision for high-affinity protein-ligand complexes in slow tumbling in the liquid state. [ABSTRACT FROM AUTHOR]

• Transformation of singlet order into heteronuclear magnetisation by the gS2hM sequence. • The gS2hM sequence works in the near-equivalence regime up to the intermediate regime. • The gS2hM sequence is insensitive to deviations in the static magnetic field and radiofrequency field strength. Several important NMR procedures involve the conversion of nuclear singlet order into heteronuclear magnetisation, including some experiments involving long-lived spin states and parahydrogen-induced hyperpolarisation. However most existing sequences suffer from a limited range of validity or a lack of robustness against experimental imperfections. We present a new radio-frequency scheme for the transformation of the singlet order of a chemically-equivalent homonuclear spin pair into the magnetisation of a heteronuclear coupling partner. The proposed radio-frequency (RF) scheme is called gS2hM (generalized singlet-to-heteronuclear magnetisation) and has good compensation for common experimental errors such as RF and static field inhomogeneities. The sequence retains its robustness for homonuclear spin pairs in the intermediate coupling regime, characterised by the in-pair coupling being of the same order of magnitude as the difference between the out-of-pair couplings. This is a substantial improvement to the validity range of existing sequences. Analytical solutions for the pulse sequence parameters are provided. Experimental results are shown for two test cases. [ABSTRACT FROM AUTHOR]

• Robust pneumatic shuttling for magnetic field cycling. • Accurate relaxation and lifetime measurements at variable fields. • Automated SABRE hyperpolarization enables multi-scan measurements. • Hyperpolarized multidimensional spectra facilitate study of chemical dynamics. We present a simple-to-implement pneumatic sample shuttle for automation of magnetic field cycling and multidimensional NMR. The shuttle system is robust allowing automation of hyperpolarized and non-hyperpolarized measurements, including variable field lifetime measurements, SABRE polarization optimization, and SABRE multidimensional experiments. Relaxation-protected singlet states are evaluated by variable-field T 1 and T S measurements. Automated shuttling facilitates characterization of hyperpolarization dynamics, field dependence and polarization buildup rates. Furthermore, reproducible hyperpolarization levels at every shuttling event enables automated 2D hyperpolarized NMR, including the first inverse 15N/1H HSQC. We uncover binding mechanisms of the catalytic species through cross peaks that are not accessible in standard one-dimensional hyperpolarized experiments. The simple design of the shuttling setup interfaced with standard TTL signals allows easy adaptation to any standard NMR magnet. [ABSTRACT FROM AUTHOR]

The formation and hyperpolarization of an [Ir(H) 2 (amine)(IMes)(η 2 -imine)]Cl complex that can be created in a hyperpolarized nuclear singlet state is reported. These complexes are formed when an equilibrium mixture of pyruvate, amine (benzylamine or phenylethylamine), and the corresponding imine condensation product, react with preformed [Ir(H) 2 (amine) 3 (IMes)]Cl. These iridium α-carboxyimine complexes exist as two regioisomers differentiated by the position of amine. When examined with para-hydrogen the hydride resonances of the isomer with amine trans to hydride become strongly hyperpolarized. The initial hydride singlet states readily transfer to the corresponding 13 C 2 state in the labelled imine and exhibit magnetic state lifetimes of up to 11 seconds. Their 13 C signals have been detected with up to 420 fold signal gains at 9.4 T. On a longer timescale, and in the absence of H 2 , further reaction leads to the formation of neutral carbonate containing [Ir(amine)(η 2 -CO 3 )(IMes)(η 2 -imine)]. Complexes are characterized by, IR, MS, NMR and X-ray diffraction., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Carotenoids are essential light-harvesting pigments in natural photosynthesis. They absorb in the blue-green region of the solar spectrum and transfer the absorbed energy to (bacterio-)chlorophylls, and thus expand the wavelength range of light that is able to drive photosynthesis. This process is an example of singlet-singlet excitation energy transfer, and carotenoids serve to enhance the overall efficiency of photosynthetic light reactions. The photochemistry and photophysics of carotenoids have often been interpreted by referring to those of simple polyene molecules that do not possess any functional groups. However, this may not always be wise because carotenoids usually have a number of functional groups that induce the variety of photochemical behaviours in them. These differences can also make the interpretation of the singlet excited states of carotenoids very complicated. In this article, we review the properties of the singlet excited states of carotenoids with the aim of producing as coherent a picture as possible of what is currently known and what needs to be learned., (© 2018 The Author(s).)

This paper discusses methodology developed over the past 12years in order to access and manipulate singlet order in systems comprising two coupled spin-1/2 nuclei in liquid-state nuclear magnetic resonance. Pulse sequences that are valid for different regimes are discussed, and fully analytical proofs are given using different spin dynamics techniques that include product operator methods, the single transition operator formalism, and average Hamiltonian theory. Methods used to filter singlet order from byproducts of pulse sequences are also listed and discussed analytically. The theoretical maximum amplitudes of the transformations achieved by these techniques are reported, together with the results of numerical simulations performed using custom-built simulation code., (Copyright © 2016 Elsevier B.V. All rights reserved.)