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[en] Femtosecond high-order harmonic transient absorption spectroscopy is used to observe electromagnetically induced transparency-like behavior as well as induced absorption in the extreme ultraviolet by laser dressing of the He 2s2p (1P0) and 2p2 (1Se) double excitation states with an intense 800 nm field. Probing in the vicinity of the 1s2 → 2s2p transition at 60.15 eV reveals the formation of an Autler-Townes doublet due to coherent coupling of the double excitation states. Qualitative agreement with the experimental spectra is obtained only when optical field ionization of both double excitation states into the N = 2 continuum is included in the theoretical model. Because the Fano q-parameter of the unperturbed probe transition is finite, the laser-dressed He atom exhibits both enhanced transparency and absorption at negative and positive probe energy detunings, respectively
[en] Highlights: ► Laser-induced filamentation was examined using emission spectroscopy. ► Cation and triplet state dynamics were examined. ► Triplet states are populated by intersystem crossing from excited singlet states. ► Neutralization of cations to populate triplet states is a minor pathway. ► Measured electron densities were found to be lower than has been proposed previously. -- Abstract: It has been suggested that the process of laser induced filamentation can be used in a wide range of applications such as: material processing, controlled electric discharge, and innovative spectroscopic measurements including the remote sensing of pollutants and hazardous materials. During filamentation, emissions from small excited molecular species and atomic states, both neutral and ionic, are readily observed. Among the important excited state species observed in air is the excited triplet state of molecular nitrogen, N2(C3Πu). A method used to measure the emission properties of the excited states of nitrogen during filamentation is described. These measurements indicate that intersystem crossing from an excited singlet state is the dominate path to produce the triplet state. Alternative pathways, including neutralization of cationic species, were shown to be minor contributors under the laser-induced filamentation conditions of this study.
[en] Highlights: ► The carbonyl overtone of acetone clusters is observed by IR-VUV spectroscopy. ► Acetone molecules in the dimer are stacked with an antiparallel way. ► The structure of the acetone trimer and the tetramer are the cyclic structures. ► The carbonyl groups would interact with the methyl groups in acetone clusters. ► These weak interactions are further confirmed by H/D substitution experiment. -- Abstract: Size-selected IR–VUV spectroscopy is employed to detect vibrational characteristics in the region 2850 ∼ 3550 cm−1 of neutral acetone and its clusters (CH3COCH3)n (n = 1–4). Features around 3440 cm−1 in the spectra of acetone monomer and its clusters are assigned to the carbonyl stretch (CO) overtone. These features red-shift from 3455 to 3433 cm−1 as the size of the clusters increases from the monomer to the tetramer. Based on calculations, the experimental IR spectra in the C=O overtone region suggest that the dominant structures for the acetone trimer and tetramer should be cyclic in the supersonic expansion sample. This study also suggests that the carbonyl groups interact with the methyl groups in the acetone clusters. These weak interactions are further confirmed by the use of deuterium substitution.
[en] Highlights: ► Weak hydrophilic nature of Cl-terminated Ge surface. ► Growth of LB film on weak hydrophilic surface. ► Limitation of CA measurement which is overcome by LB technique. -- Abstract: The hydrophilic/hydrophobic nature of the Cl-passivated Ge(0 0 1) surface is investigated directly by contact angle (CA) measurement and indirectly by growing nickel arachidate Langmuir–Blodgett (LB) films on the Cl-passivated Ge(0 0 1) surface. Passivation of Ge(0 0 1) surface by Cl atoms is confirmed by X-ray photoelectron spectroscopy measurement. CA measurements show that the Cl-passivated Ge(0 0 1) surface has intermediate wettability, i.e., the surface has intermediate hydrophilic/hydrophobic behavior. Structural information obtained from the deposited LB films by using X-ray reflectivity and atomic force microscopy analysis shows that the surface is homogeneous and hydrophilic (∼85%), although very few effectively hydrophobic (∼15%) regions are present. Structural study in molecular level thus helps to identify the surface nature in nanometer level, which is not possible by simple macroscopic CA measurement. Specific electrostatic and dispersive effects of Cl atoms are possibly responsible for such hydrophilic-like nature of the Cl-passivated Ge(0 0 1) surface.
[en] Highlights: ► Laser-ablated ruthenium or osmium atom reactions with CO and NO mixtures in solid argon. ► Metal carbonyl nitrosyls including M(CO)(NO) and 18-electron configuration M(CO)2(NO)2 molecules (M = Ru, Os). ► The observed absorption bands of reaction products are identified by isotopic substitution and DFT calculations. ► The bonding and reaction mechanism are discussed in detail. -- Abstract: Laser-ablated ruthenium or osmium atom reactions with CO and NO mixtures in solid argon produce unsaturated metal carbonyl nitrosyls including M(CO)(NO) and 18-electron configuration M(CO)2(NO)2 molecules (M = Ru, Os). The observed absorption bands of reaction products are identified by isotopic substitution, isotopic ratios and isotopic distributions (13CO, 15NO, and mixtures). DFT (B3LYP and BP86) vibrational fundamental calculations reproduce observed frequencies and isotopic shifts very well. The bonding and reaction mechanism are discussed.
[en] Highlights: ► Velocity map imaging spectrometer optimised for molecular photoionisation dynamics. ► Kinetic energy distribution of O+ fragments measured. ► Effect of autoionisation on photoelectron vibrational populations studied. -- Abstract: The design, construction and performance of a velocity map imaging spectrometer for the study of molecular photoionisation dynamics is described. The spectrometer has been optimised for the efficient collection and detection of particles (electrons or positively charged ions) generated through the interaction of gas phase molecules with synchrotron radiation. A double Einzel lens, incorporated into the flight tube, enhances the collection efficiency of energetic particles. Computer modelling has been used to trace the trajectories of charged particles through the spectrometer and to assess the image quality. A time and position sensitive delay-line detector is used to record the images. Results from two experimental studies are presented to illustrate the capabilities of the spectrometer. In the first, the effect of electronic autoionisation on the vibrationally resolved photoelectron branching ratios of the N2+ X 2Σg+ state has been investigated in an excitation range where prominent structure due to Rydberg states occurs in the ion yield curve. The results show that autoionisation leads to rotational branch populations that differ from those observed in direct, non-resonant, photoionisation. In the second, the kinetic energy distribution and the angular distribution of O+ fragments formed in the dissociative photoionisation of molecular oxygen have been measured. The timing properties of the detector have allowed O+ fragments to be separated from O2+ parent ions using time-of-flight techniques.
[en] Graphical abstract: Optimized fully relativistic calculations of NMR J-couplings (HBr, HI), chemical shifts (Si, Sn) and absolute shielding for reference compounds of heavy atoms (Si, Sn) are given. Highlights: ► In this article we show a procedure to get accurate NMR σRef of Si and Sn. ► Calculations of σ on more than three heavy-atom-containing molecules are given. ► Our results are closer to δexp than previous calculations for SnX4 (X = H, Cl, Br, I). ► Optimized basis sets were considered for full R and NR calculations of NMR J and σ. ► Relativistic effects enlarge electron correlation effects on J-couplings. - Abstract: The NMR spectroscopic parameters are largely influenced by relativistic effects. They are highly dependent on the electronic behavior inside the spatial regions occupied by nuclei. Full relativistic calculations of indirect nuclear spin–spin couplings at random phase level of approach (RPA) in the title compounds with reoptimized Dyall cVTZ basis sets are given. A comparison with the results of calculations with other basis sets that are mostly used within the non-relativistic (NR) domain is presented. We analyzed the dependence of that couplings with the speed of light over the whole range of values, from the full relativistic to the NR regimes. Within this last regime, calculations at the second-order level of approach (SOPPA) indicated that electron correlation effects may not be as important for nuclear magnetic shieldings, but they must be included with care for J-coupling calculations. From these calculations, we determined that relativity enlarges the electron correlation effects of the J-couplings of HBr and HI. Because the results of nuclear magnetic shielding calculations within polarization propagators at the RPA level were reliable, we were able to show a new and easy procedure to obtain absolute nuclear magnetic shieldings on reference compounds for both Si and Sn nuclei: σ[Si (CH3)4] = 421.28 ± 29.33 ppm and σ[Sn (CH3)4] = 3814.96 ± 79.12 ppm. They were obtained from experimental chemical shifts and accurate nuclear magnetic shielding calculations on different molecular systems.
[en] Graphical abstract: The 4c-DFT calculations were performed for M2 and MAu (M = K though element 119). Trends in atomic and molecular properties are shown to be reversed in group 1 beyond Cs due to relativity. The 8s(119) AO relativistic stabilization and contraction is the reason for the weakest M–Au bond and smallest adsorption enthalpy of element 119 on noble metals in group 1. Highlights: ► Fully relativistic 4c-DFT calculations were performed for M2 and MAu (M = K though element 119). ► Trends in atomic and molecular properties are reversed in group 1 from Cs on due to relativity. ► The 8s(119) AO stabilization and contraction result in the weakest M–Au bond in group 1. ► The weakest adsorption of element 119 on noble metals is expected among all group-1 elements. - Abstract: Spectroscopic properties of group-1 M2 and MAu (M = K, Rb, Cs, Fr, and element 119) were calculated using the 4c-DFT method. The results show that the relativistic contraction and stabilization of the ns(M) AO result in the inversion of trends both in atomic and molecular properties in group 1 beyond Cs. Electronegativity χ of the elements proves to decrease from Cs, the most electropositive element of all elements, to element 119, with its χ value approaching that of Na. Due to the largest relativistic effects on the 8s(119) AO in group 1, bonding in (119)2 appears to be stronger than that of K2, while bonding in 119Au should be the weakest out of all group-1 MAu. Using calculated dissociation energies of M2, sublimation enthalpies, ΔHsub, of Fr of 77 kJ/mol and element 119 of 94 kJ/mol were estimated using a linear correlation between these quantities in the chemical group. Using the M–Au binding energies, the adsorption enthalpies, −ΔHads, of 106 kJ/mol on gold, 76 kJ/mol on platinum, and 63 kJ/mol on silver were estimated for element 119 via a correlation with known ΔHads in the chemical group. These moderate ΔHads values are indicative of a possibility of chromatography adsorption studies of element 119 on the noble metal surfaces.
[en] Highlights: ► In this study we model the adsorption of the superheavy element 113 on gold surfaces. ► The binding energy of element 113 and thallium is calculated for cluster models. ► For many different binding sites, element 113 binds weaker by 90 ± 15 kJ/mol. - Abstract: The adsorption of thallium and element 113 atoms on a gold surface has been modelled by cluster calculations. Quasirelativistic two-component density functional calculations that include spin–orbit coupling self-consistently have been used together with spin-dependent effective core potentials. The validity of this method is demonstrated by comparisons with high-level wave function based calculations on the hetero-dimers AuTl and Au(113). New basis sets had to be generated because standard basis sets optimized for scalar-relativistic calculations are too inflexible to describe the different behaviour of the atomic sub-shells that result from the spin–orbit interaction. The topmost layer of gold atoms within the cluster was allowed to fully relax upon adsorption, and different adsorption sites (on-top, hollow, and bridge) on the (1 0 0) and (1 1 1) surfaces were considered. Spin–orbit coupling reduces the surface binding energies of an element 113 atom much more than it does for Tl, such that the binding energy of element 113 to the gold cluster, as compared to Tl, is reduced by 90 ± 15 kJ/mol in most cases. Together with the experimental result for thallium, this allows an estimate of the adsorption temperature of element 113 in thermochromatography experiments.