Browsing UA Faculty Research by Journal
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Algorithms for calculating massvelocity and Darwin relativistic corrections with nelectron explicitly correlated Gaussians with shifted centersAlgorithms for calculating the leading massvelocity (MV) and Darwin (D) relativistic corrections are derived for electronic wave functions expanded in terms of nelectron explicitly correlated Gaussian functions with shifted centers and without preexponential angular factors. The algorithms are implemented and tested in calculations of MV and D corrections for several points on the groundstate potential energy curves of the H2 and LiH molecules. The algorithms are general and can be applied in calculations of systems with an arbitrary number of electrons. Published by AIP Publishing.

Eigenstatespecific temperatures in twolevel paramagnetic spin latticesIncreasing interest in the thermodynamics of small and/or isolated systems, in combination with recent observations of negative temperatures of atoms in ultracold optical lattices, has stimulated the need for estimating the conventional, canonical temperature Tc(conv) of systems in equilibrium with heat baths using eigenstatespecific temperatures (ESTs). Four distinct ESTscontinuous canonical, discrete canonical, continuous microcanonical, and discrete microcanonicalare accordingly derived for twolevel paramagnetic spin lattices (PSLs) in external magnetic fields. At large N, the four ESTs are intensive, equal to Tc(conv), and obey all four laws of thermodynamics. In contrast, for N < 1000, the ESTs of most PSL eigenstates are nonintensive, differ from Tc(conv), and violate each of the thermodynamic laws. Hence, in spite of their similarities to Tc(conv) at large N, the ESTs are not true thermodynamic temperatures. Even so, each of the ESTs manifests a unique functional dependence on energy which clearly specifies the magnitude and direction of their deviation from Tc(conv); the ESTs are thus good temperature estimators for small PSLs. The thermodynamic uncertainty relation is obeyed only by the ESTs of small canonical PSLs; it is violated by large canonical PSLs and by microcanonical PSLs of any size. The ESTs of populationinverted eigenstates are negative (positive) when calculated using Boltzmann (Gibbs) entropies; the thermodynamic implications of these entropically induced differences in sign are discussed in light of adiabatic invariance of the entropies. Potential applications of the four ESTs to nanothermometers and to systems with longrange interactions are discussed. Published by AIP Publishing.

Electron affinity and excited states of methylglyoxalUsing photoelectron imaging spectroscopy, we characterized the anion of methylglyoxal (X(2)A" electronic state) and three lowest electronic states of the neutral methylglyoxal molecule: the closedshell singlet ground state (X(1)A'), the lowest triplet state (a(3)A"), and the openshell singlet state (A(1)A"). The adiabatic electron affinity (EA) of the ground state, EA(X(1)A') = 0.87(1) eV, spectroscopically determined for the first time, compares to 1.10(2) eV for unsubstituted glyoxal. The EAs (adiabatic attachment energies) of two excited states of methylglyoxal were also determined: EA(a(3)A") = 3.27(2) eV and EA(A(1)A") = 3.614(9) eV. The photodetachment of the anion to each of these two states produces the neutral species near the respective structural equilibria; hence, the a(3)A" < X(2)A" and A(1)A" < X(2)A" photodetachment transitions are dominated by intense peaks at their respective origins. The lowestenergy photodetachment transition, on the other hand, involves significant geometry relaxation in the X(1)A' state, which corresponds to a 60 degrees internal rotation of the methyl group, compared to the anion structure. Accordingly, the X(1)A' < X(2)A" transition is characterized as a broad, congested band, whose vertical detachment energy, VDE = 1.20(4) eV, significantly exceeds the adiabatic EA. The experimental results are in excellent agreement with the ab initio predictions using several equationofmotion methodologies, combined with coupledcluster theory. Published by AIP Publishing.

Examining transition metal hydrosulfides: The pure rotational spectrum of ZnSH (X̃2A′)The pure rotational spectrum of the ZnSH ((X) over tilde (2)A') radical has been measured using millimeterwave direct absorption and Fourier transform microwave (FTMW) methods across the frequency range 18468 GHz. This work is the first gasphase detection of ZnSH by any spectroscopic technique. Spectra of the (ZnSH)Zn66, (ZnSH)Zn68, and (ZnSD)Zn64 isotopologues were also recorded. In the mmwave study, ZnSH was synthesized in a DC discharge by the reaction of zinc vapor, generated by a Broidatype oven, with H2S; for FTMW measurements, the radical was made in a supersonic jet expansion by the same reactants but utilizing a dischargeassisted laser ablation source. Between 7 and 9 rotational transitions were recorded for each isotopologue. Asymmetry components with Ka = 0 through 6 were typically measured in the mmwave region, each split into spinrotation doublets. In the FTMW spectra, hyperfine interactions were also resolved, arising from the hydrogen or deuterium nuclear spins of I = 1/2 or I = 1, respectively. The data were analyzed using an asymmetric top Hamiltonian, and rotational, spinrotation, and magnetic hyperfine parameters were determined for ZnSH, as well as the quadrupole coupling constant for ZnSD. The observed spectra clearly indicate that ZnSH has a bent geometry. The r(m)((1)) structure was determined to be r(ZnS) = 2.213(5) angstrom, r(SH) = 1.351(3) angstrom, and theta(ZnSH) = 90.6(1)degrees, suggesting that the bonding occurs primarily through sulfur p orbitals, analogous to H2S. The hyperfine constants indicate that the unpaired electron in ZnSH primarily resides on the zinc nucleus. Published by AIP Publishing.

Millimeterwave spectroscopy of CrC (X3Σ−) and CrCCH (X̃ 6Σ+): Examining the chromiumcarbon bondPure rotational spectroscopy of the CrC (X3 Sigma()) and CrCCH ((X) over tilde (6)Sigma(+)) radicals has been conducted using millimeter/submillimeter direct absorption methods in the frequency range 225585 GHz. These species were created in an AC discharge of Cr(CO)(6) and either methane or acetylene, diluted in argon. Spectra of the CrCCD were also recorded for the first time using deuterated acetylene as the carbon precursor. Seven rotational transitions of CrC were measured, each consisting of three widely spaced, fine structure components, arising from spinspin and spinrotation interactions. Eleven rotational transitions were recorded for CrCCH and five for CrCCD; each transition in these cases was composed of a distinct fine structure sextet. These measurements confirm the respective (3)Sigma() and (6)Sigma(+) ground electronic states of these radicals, as indicated from optical studies. The data were analyzed using a Hund's case (b) Hamiltonian, and rotational, spinspin, and spinrotation constants have been accurately determined for all three species. The spectroscopic parameters for CrC were significantly revised from previous optical work, while those for CrCCH are in excellent agreement; completely new constants were established for CrCCD. The chromiumcarbon bond length for CrC was calculated to be 1.631 angstrom, while that in CrCCH was found to be r(CrC) = 1.993 angstrom  significantly longer. This result suggests that a single CrC bond is present in CrCCH, preserving the acetylenic structure of the ligand, while a triple bond exists in CrC. Analysis of the spin constants suggests that CrC has a nearby excited (1)Sigma(+) state lying similar to 16 900 cm(1) higher in energy, and CrCCH has a (6)Pi excited state with E similar to 4800 cm(1). Published by AIP Publishing.

A molecular dynamics study of the role of molecular water on the structure and mechanics of amorphous geopolymer bindersIn this paper, molecular dynamics simulations are used to study the effect of molecular water and composition (Si/Al ratio) on the structure and mechanical properties of fully polymerized amorphous sodium aluminosilicate geopolymer binders. The Xray pair distribution function for the simulated geopolymer binder phase showed good agreement with the experimentally determined structure in terms of bond lengths of the various atomic pairs. The elastic constants and ultimate tensile strength of the geopolymer binders were calculated as a function of water content and Si/Al ratio; while increasing the Si/Al ratio from one to three led to an increase in the respective values of the elastic stiffness and tensile strength, for a given Si/Al ratio, increasing the water content decreased the stiffness and strength of the binder phase. An atomicscale analysis showed a direct correlation between water content and diffusion of alkali ions, resulting in the weakening of the AlO4 tetrahedral structure due to the migration of charge balancing alkali ions away from the tetrahedra, ultimately leading to failure. In the presence of water molecules, the diffusion behavior of alkali cations was found to be particularly anomalous, showing dynamic heterogeneity. This paper, for the first time, proves the efficacy of atomistic simulations for understanding the effect of water in geopolymer binders and can thus serve as a useful design tool for optimizing composition of geopolymers with improved mechanical properties. Published by AIP Publishing.

Orbitorbit relativistic correction calculated with allelectron molecular explicitly correlated GaussiansAn algorithm for calculating the firstorder electronic orbitorbit magnetic interaction correction for an electronic wave function expanded in terms of allelectron explicitly correlated molecular Gaussian (ECG) functions with shifted centers is derived and implemented. The algorithm is tested in calculations concerning the H2 molecule. It is also applied in calculations for LiH and H3(+) molecular systems. The implementation completes our work on the leading relativistic correction for ECGs and paves the way for very accurate ECG calculations of ground and excited potential energy surfaces (PESs) of small molecules with two and more nuclei and two and more electrons, such as HeH, H3(+), HeH2+, and LiH2+. The PESs will be used to determine rovibrational spectra of the systems. Published by AIP Publishing.