Anisotropie dipole polarizabilities and quadrupole moments of open-shell atoms and ions: O, F, S, Cl, Se, Br and isoelectronic systems

Kinetics and Mechanism of the Singlet Oxygen Atom Reaction with Dimethyl Ether

We combine in situ laser spectroscopy, quantum chemistry, and kinetic calculations to study the reaction of a singlet oxygen atom with dimethyl ether. Infrared laser absorption spectroscopy and Faraday rotation spectroscopy are used for the detection and quantification of the reaction products OH, H2O, HO2, and CH2O on submillisecond time scales. Fitting temporal profiles of products with simulations using an in-house reaction mechanism allows product branching to be quantified at 30, 60, and 150 Torr. The experimentally determined product branching agrees well with master equation calculations based on electronic structure data and transition state theory. The calculations demonstrate that the dimethyl peroxide (CH3OOCH3) generated via O-insertion into the C-O bond undergoes subsequent dissociation to CH3O + CH3O through energetically favored reactions without an intrinsic barrier. This O-insertion mechanism can be important for understanding the fate of biofuels leaking into the atmosphere and for plasma-based biofuel processing technologies.

Low Energy Positron Scattering by F and F2

We have determined integral and differential elastic cross sections for positron scattering with atomic F and F₂ molecules from 0.01 to 1000 eV with different theoretical approaches. Higher order polarizabilities were successively considered in the scattering potential, and we observed that the differential and integral cross sections converge only when the pure dipole second hyperpolarization level is taken into account, demonstrating the importance of the hyperpolarization effects on the low energy positron scattering dynamics. Ramsauer structures were found for both targets, and in the particular case of the F atom, the effect of its quadrupole moment proved to be relevant around the position of the Ramsauer minimum, which was determined together with the scattering length for each of the adopted polarization schemes. A relation of these quantities with the matching radius between the correlation and polarization interactions is also discussed. Agreement between the model potential and ab initio cross sections for the lowest level of target polarization is found for F₂. Since there is no previous theoretical or experimental determination of cross sections for these targets, we compared the differential cross sections of F₂ with experimental data available for N₂ and O₂ and found reasonable agreement.

Novel Molecular Doping Mechanism for n-Doping of SnO2 via Triphenylphosphine Oxide and Its Effect on Perovskite Solar Cells

Molecular doping of inorganic semiconductors is a rising topic in the field of organic/inorganic hybrid electronics. However, it is difficult to find dopant molecules which simultaneously exhibit strong reducibility and stability in ambient atmosphere, which are needed for n-type doping of oxide semiconductors. Herein, successful n-type doping of SnO₂ is demonstrated by a simple, air-robust, and cost-effective triphenylphosphine oxide molecule. Strikingly, it is discovered that electrons are transferred from the R3P⁺ O^- σ-bond to the peripheral tin atoms other than the directly interacted ones at the surface. That means those electrons are delocalized. The course is verified by multi-photophysical characterizations. This doping effect accounts for the enhancement of conductivity and the decline of work function of SnO₂ , which enlarges the built-in field from 0.01 to 0.07 eV and decreases the energy barrier from 0.55 to 0.39 eV at the SnO₂ /perovskite interface enabling an increase in the conversion efficiency of perovskite solar cells from 19.01% to 20.69%.

Experimental and theoretical study of the collisional quenching of S(1D) by Ar

We present an experimental and theoretical investigation of the deactivation rate of S(¹D) atoms by collisions with argon.

Diffusion of atomic oxygen relevant to water formation in amorphous interstellar ices

Molecular dynamics (MD) simulations together with accurate physics-based force fields are employed to determine the mobility of atomic oxygen in amorphous ice at low temperatures, characteristic for conditions in interstellar ices. From the simulations it is found that the mobility of atomic oxygen ranges from 60 to 480 Ų ns⁻¹ in amorphous ice at temperatures between 50 and 200 K. Hence, the simulations establish that atomic oxygen is mobile to a certain degree and a chemical mechanism for water formation involving oxygen mobility is a realistic scenario. This is also confirmed by the computed migration barriers for oxygen diffusion by multiple umbrella sampling simulations, which yield barriers for diffusion in the range of 0.7–1.9 kcal mol⁻¹. The physics-based force field – based on a multipolar expansion of the electrostatic interactions – yields more pronounced energetics for oxygen migration pathways compared to the conventional point-charge models employed in typical simulations. Once formed, the computed solvation free energy suggests that atomic oxygen thermodynamically prefers to be localized inside amorphous ice and is available for chemical reaction, which may be relevant to water formation in and on grains.

The X+ 2Πg, A+ 2Πu, B+ 2Δu, and a+ 4Σu(-) electronic states of Cl2(+) studied by high-resolution photoelectron spectroscopy

Partially rotationally resolved pulsed-field-ionization zero-kinetic-energy photoelectron spectra of the three isotopomers ((35)Cl2, (35)Cl(37)Cl, and (37)Cl2) of Cl2 have been recorded in the wavenumber ranges 92,500-96,500 cm(-1), corresponding to transitions to the low vibrational levels of the X(+) (2)Πg (Ω = 3∕2, 1∕2) ground state of Cl2 (+), and 106,750-115,500 cm(-1), where the a(+) (4)Σu (-)←X(1)Σg (+), A(+) (2)Πu←X(1)Σg (+), and B(+) (2)Δu←X(1)Σg (+) band systems overlap with transitions to high vibrational levels (v(+) > 25) of the X(+) state. The observation of Franck-Condon-forbidden transitions to vibrational levels of the X(+) state of the cation with v(+) ≥ 25 is rationalized by a mechanism involving vertical excitation of predissociative Rydberg states of mixed singlet-triplet character with an A(+) ion core which are coupled to Rydberg states converging to high-v(+) levels of the X(+) state. The same mechanism is proposed to also be responsible for the observation of Cl(+) - Cl(-) ion pairs and quartet states in the photoionization of Cl2. The potential energy function of the X(+) state of Cl2 (+) was determined in a direct fit to the experimental data. Transitions to vibrational levels of the A(+) (2)Πu, 3∕2 and B(+) (2)Δu, 3∕2 states of Cl2 (+) could be identified using the results of a recent analysis of the strong perturbation between the A(+) (2)Πu, 3∕2 and B(+) (2)Δu, 3∕2 states of Cl2 (+) observed in the A(+) - X(+) band system [Gharaibeh et al., J. Chem. Phys. 137, 194317 (2012)], and transitions to several vibrational levels of the upper spin-orbit component ((2)Πu, 1∕2) of the A(+) state were detected in the photoelectron spectrum of Cl2 (+). The a(+) (4)Σu (-)←X(1)Σg (+) photoelectron band system, which is nominally forbidden by single-photon ionization from the ground state was also observed for the first time and its vibrational and spin-orbit structures were analyzed. The (4)Σu (-) state is split into two spin-orbit components with Ω = 1∕2 and Ω = 3∕2, separated by 37.5 cm(-1). The vibrational energy level structure of both components is regular, which indicates that the splitting results from the interaction with one or more distant ungerade Ω = 1∕2 or Ω = 3∕2 electronic states.

Superior optical properties of homogeneous liquid crystal alignment on a tin (IV) oxide surface sequentially modulated via ion beam irradiation

We first investigated the alignment characteristics of tin (IV) oxide (SnO(2)) thin films deposited by radio-frequency (RF) magnetron sputtering. This study demonstrates that liquid crystal (LC) molecules could be aligned homogeneously by controlling the Ion Beam (IB) irradiation energy densities. We also show that the pretilt angle of the LC molecules has a close relation with the surface energy. X-ray photoelectron spectroscopy (XPS) indicates that a non-stoichiometric SnO(2-x) surface converted by ion beam irradiation can horizontally align the LC molecules. The measured electro-optical (EO) characteristics showed high performance, comparable with those of rubbed and ion-beam irradiated polyimide (PI) layers.

Interactions in open-shell clusters: ab initio study of pre-reactive complex O(3P) + HCl

Van der Waals interactions between the ground-state triplet O(3P) atom and the closed-shell HCl molecule are investigated in the pre-reactive region. Three adiabatic (two of A'' symmetry and one of A' symmetry) and four non-relativistic diabatic potential energy surfaces are obtained by combining a restricted open-shell coupled cluster approach with the multireference configuration interaction method. The lower A'' adiabatic potential surface has a single minimum (D(e) = 589 cm(-1)) for a linear O...HCl configuration. The upper A'' potential has a weak (D(e) = 65 cm(-1)) minimum for a linear HCl...O configuration. The A' adiabatic potential has a weak (124 cm(-1)) T-shaped minimum. Adiabatic potentials intersect once in the O...HCl linear configuration and twice in the linear HCl...O geometry. The role of electrostatic interactions in shaping these potentials is discussed. The effects of spin-orbit coupling on this interaction are also investigated assuming a constant value of the SO parameter.

Polarizabilities and hyperpolarizabilities for the atoms Al, Si, P, S, Cl, and Ar: Coupled cluster calculations

Accurate static dipole polarizabilities and hyperpolarizabilities are calculated for the ground states of the Al, Si, P, S, Cl, and Ar atoms. The finite-field computations use energies obtained with various ab initio methods including Moller-Plesset perturbation theory and the coupled cluster approach. Excellent agreement with experiment is found for argon. The experimental alpha for Al is likely to be in error. Only limited comparisons are possible for the other atoms because hyperpolarizabilities have not been reported previously for most of these atoms. Our recommended values of the mean dipole polarizability (in the order Al-Ar) are alpha/e(2)a(0) (2)E(h) (-1)=57.74, 37.17, 24.93, 19.37, 14.57, and 11.085 with an error estimate of +/-0.5%. The recommended values of the mean second dipole hyperpolarizability (in the order Al-Ar) are gamma/e(4)a(0) (4)E(h) (-3)=2.02 x 10(5), 4.31 x 10(4), 1.14 x 10(4), 6.51 x 10(3), 2.73 x 10(3), and 1.18 x 10(3) with an error estimate of +/-2%. Our recommended polarizability anisotropy values are Deltaalpha/e(2)a(0) (2)E(h) (-1)=-25.60, 8.41, -3.63, and 1.71 for Al, Si, S, and Cl respectively, with an error estimate of +/-1%. The recommended hyperpolarizability anisotropies are Deltagamma/e(4)a(0) (4)E(h) (-3)=-3.88 x 10(5), 4.16 x 10(4), -7.00 x 10(3), and 1.65 x 10(3) for Al, Si, S, and Cl, respectively, with an error estimate of +/-4%.

Potential energy curves of diatomic molecular ions from high-resolution photoelectron spectroscopy. I. The first six electronic states of Ar2+

High-resolution photoelectron spectroscopic data have been used to determine the potential energy curves of the first six electronic states of Ar2+. The potential energy functions properly include the effects of the long-range interactions and of the spin-orbit interaction and are of spectroscopic accuracy (1-2 cm(-1)) over a wide range of internuclear distances. The total number of adjustable parameters could be reduced to only 12 by truncating the long-range interaction series after the R(-6) term and assuming an R-independent spin-orbit coupling constant. This assumption was verified to be valid to an accuracy of +/-2 cm(-1) over the range of internuclear distances between 3.0 and 4.6 A. The interaction potential proposed by Siska [P. E. Siska, J. Chem. Phys. 85, 7497 (1986)] was generalized to a form that is expected to be sufficiently flexible to describe chemical bonding in other diatomic molecular ions. The potential energy curves are more accurate than the best available ab initio curves by two orders of magnitude and provide quantitative information on dissociation energies and equilibrium internuclear distances. The local maximum between the two potential wells of the I(1/2g) state was determined to lie 62 cm(-1) below the Ar(1S0)+Ar(+)(2P(3/2)) dissociation limit, and the II(1/2g) state is found to be significantly more bound (De=177 cm(-1)) than previously assumed.