Variational treatment of electron-polyatomic molecule scattering calculations using adaptive overset grids

The Complex Kohn variational method for electron-polyatomic molecule scattering is formulated using an overset grid representation of the scattering wave function. The overset grid consists of a central grid and multiple dense, atom-centered subgrids that allow the simultaneous spherical expansions of the wave function about multiple centers. Scattering boundary conditions are enforced by using a basis formed by the repeated application of the free particle Green's function and potential, $\hat{G}^+_0\hat{V}$ on the overset grid in a "Born-Arnoldi" solution of the working equations. The theory is shown to be equivalent to a specific Pad\'e approximant to the $T$-matrix, and has rapid convergence properties, both in the number of numerical basis functions employed and the number of partial waves employed in the spherical expansions. The method is demonstrated in calculations on methane and CF$_4$ in the static-exchange approximation, and compared in detail with calculations performed with the numerical Schwinger variational approach based on single center expansions. An efficient procedure for operating with the free-particle Green's function and exchange operators (to which no approximation is made) is also described

Solving the Coulomb scattering problem using the complex scaling method

Based on the work of Nuttall and Cohen [Phys. Rev. {\bf 188} (1969) 1542] and Resigno et al{} [Phys. Rev. A {\bf 55} (1997) 4253] we present a rigorous formalism for solving the scattering problem for long-range interactions without using exact asymptotic boundary conditions. The long-range interaction may contain both Coulomb and short-range potentials. The exterior complex scaling method, applied to a specially constructed inhomogeneous Schr\"odinger equation, transforms the scattering problem into a boundary problem with zero boundary conditions. The local and integral representations for the scattering amplitudes have been derived. The formalism is illustrated with numerical examples.Comment: 3 pages, 3 figure

Probing autoionizing states of molecular oxygen with XUV transient absorption: Electronic symmetry dependent lineshapes and laser induced modification

The dynamics of autoionizing Rydberg states of oxygen are studied using attosecond transient absorption technique, where extreme ultraviolet (XUV) initiates molecular polarization and near infrared (NIR) pulse perturbs its evolution. Transient absorption spectra show positive optical density (OD) change in the case of $ns\sigma_g$ and $nd\pi_g$ autoionizing states of oxygen and negative OD change for $nd\sigma_g$ states. Multiconfiguration time-dependent Hartree-Fock (MCTDHF) calculation are used to simulate the transient absorption spectra and their results agree with experimental observations. The time evolution of superexcited states is probed in electronically and vibrationally resolved fashion and we observe the dependence of decay lifetimes on effective quantum number of the Rydberg series. We model the effect of near-infrared (NIR) perturbation on molecular polarization and find that the laser induced phase shift model agrees with the experimental and MCTDHF results, while the laser induced attenuation model does not. We relate the electron state symmetry dependent sign of the OD change to the Fano parameters of the static absorption lineshapes.Comment: 15 pages, 8 figure

Ultrafast Rydberg-state dissociation in oxygen: Identifying the role of multielectron excitations

We investigated the fragmentation dynamics of highly excited states of molecular oxygen using femtosecond transient photoelectron spectroscopy. An extreme ultraviolet (XUV) pulse populates the autoionizing Rydberg series converging to O-2(+) c(4)Sigma(-)(u), and a femtosecond near-infrared (IR) pulse was used to photoionize these states as they dissociate. Monitoring the differential photoelectron spectra as a function of time delay allowed us to obtain the relaxation lifetimes of these Rydberg states. We observed a photoelectron signal corresponding to the formation of a 4p excited atomic oxygen fragment, which is not an expected dissociation product of the (O-2(+) c(4)Sigma(-)(u))nl sigma(g) Rydberg series. Analysis of the time-dependent photoelectron spectra and photoionization calculations indicate that this fragment results from a previously unexplored (O-2(+) (4)Pi(g))4p repulsive state and that, contrary to expectations, this multielectron excitation pathway presents a substantial cross section. Our study demonstrates that two-color time-resolved differential photoelectron spectroscopy is an excellent tool to study the fragmentation dynamics of such multielectron excited states, which are not easily probed by other means.US Army Research Laboratory; U.S. Army Research Office [W911NF-14-1-0383]; National Science Foundation (NSF) [PHY-1505556]; U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES) [DE-SC0018251]; US Department of Energy Chemical Sciences, Geosciences, and Biosciences Division [DE-AC02-05CH11231]This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Dissociative electron attachment to the H2O molecule. I. Complex-valued potential-energy surfaces for the 2B1, 2A1, and 2B2 metastable states of the water anion

We present the results of calculations defining global, three-dimensional representations of the complex-valued potential-energy surfaces of the doublet B1, doublet A1, and doublet B2 metastable states of the water anion that underlie the physical process of dissociative electron attachment to water. The real part of the resonance energies is obtained from configuration-interaction calculations performed in a restricted Hilbert space, while the imaginary part of the energies (the widths) is derived from complex Kohn scattering calculations. A diabatization is performed on the 2A1 and 2B2 surfaces, due to the presence of a conical intersection between them. We discuss the implications that the shapes of the constructed potential-energy surfaces will have upon the nuclear dynamics of dissociative electron attachment to H2O. This work originally appeared as Phys Rev A 75, 012710 (2007). Typesetting errors in the published version have been corrected here.Comment: Corrected version of PRA 75, 012710 (2007

Surface colour change in wood during drying above and below fibre saturation point

A technique, useful for studying the formation of kiln brown stain in wood drying, has been developed to measure the surface colour change in a single board wood sample during drying.  The wood sample is planed carefully in the green state to remove any surface wood that was damaged during cutting.  The intact tracheids at the surface cause the evaporative front to remain at the surface during drying and therefore colour formation also occurs right at the surface. In this way, the colour can be measured using a spectrophotometer at various stages during drying without having to slice the sample.Experiments were carried out to measure the change in colour of wood from green to EMC corresponding to the drying schedule used.  At the end of each schedule the boards were held at the EMC to determine how the colour changed below fibre saturation point.  The results show that the colour of the wood continues to change below the fibre saturation point and the nature of the colour change indicates an increase in the complexity of the coloured compounds present.Further experiments were done to measure the rate of colour development at different temperatures using the technique developed.  The results have shown a correlation between temperature and colour development over the range 50ºC to 70ºC with the rate increasing significantly above 60ºC

Dissociative electron attachment to the H2O molecule. II. Nuclear dynamics on coupled electronic surfaces within the local complex potential model

We report the results of a first-principles study of dissociative electron attachment to H2O. The cross sections are obtained from nuclear dynamics calculations carried out in full dimensionality within the local complex potential model by using the multi-configuration time-dependent Hartree method. The calculations employ our previously obtained global, complex-valued, potential-energy surfaces for the three (doublet B1, doublet A1, and doublet B2) electronic Feshbach resonances involved in this process. These three metastable states of H2O- undergo several degeneracies, and we incorporate both the Renner-Teller coupling between the B1 and A1 states as well as the conical intersection between the A1 and B2 states into our treatment. The nuclear dynamics are inherently multidimensional and involve branching between different final product arrangements as well as extensive excitation of the diatomic fragment. Our results successfully mirror the qualitative features of the major fragment channels observed, but are less successful in reproducing the available results for some of the minor channels. We comment on the applicability of the local complex potential model to such a complicated resonant system.Comment: Corrected version of Phys Rev A 75, 012711 (2007

Predicting participation in group parenting education in an Australian sample: The role of attitudes, norms, and control factors

We examined the theory of planned behavior (TPB) in predicting intentions to participate in group parenting education. One hundred and seventy-six parents (138 mothers and 38 fathers) with a child under 12 years completed TPB items assessing attitude, subjective norms, perceived behavioral control (PBC), and two additional social influence variables (self-identity and group norm). Regression analyses supported the TPB predictors of participation intentions with self-identity and group norm also significantly predicting intentions. These findings offer preliminary support for the TPB, along with additional sources of social influence, as a useful predictive model of participation in parenting education

An efficient basis set representation for calculating electrons in molecules

The method of McCurdy, Baertschy, and Rescigno, J. Phys. B, 37, R137 (2004) is generalized to obtain a straightforward, surprisingly accurate, and scalable numerical representation for calculating the electronic wave functions of molecules. It uses a basis set of product sinc functions arrayed on a Cartesian grid, and yields 1 kcal/mol precision for valence transition energies with a grid resolution of approximately 0.1 bohr. The Coulomb matrix elements are replaced with matrix elements obtained from the kinetic energy operator. A resolution-of-the-identity approximation renders the primitive one- and two-electron matrix elements diagonal; in other words, the Coulomb operator is local with respect to the grid indices. The calculation of contracted two-electron matrix elements among orbitals requires only O(N log(N)) multiplication operations, not O(N^4), where N is the number of basis functions; N = n^3 on cubic grids. The representation not only is numerically expedient, but also produces energies and properties superior to those calculated variationally. Absolute energies, absorption cross sections, transition energies, and ionization potentials are reported for one- (He^+, H_2^+ ), two- (H_2, He), ten- (CH_4) and 56-electron (C_8H_8) systems.Comment: Submitted to JC