Time-Dependent Density Functional Theory Investigation of the Ground and Excited States of Coumarins 102, 152, 153, and 343

We present calculations of various properties of the ground and excited electronic states of coumarins 102, 152, 153, and 343. Using density functional theory (DFT) and time-dependent density functional theory (TDDFT), we examine the excitation energies to the S1 and S2 states, the ground and excited-state dipole moments, and the lowest ionization potentials of these coumarins. In the case of C153, we locate two distinct S0 minima due to differing conformations of the julolidyl ring structure and compare properties for the syn and anti conformers. For C343, we examine the possibility of proton transfers in the ground and S1 states of the system. We find that (1) DFT tends to overestimate the ground-state dipole moments in these systems, (2) excellent agreement is obtained between TDDFT and experimental vertical excitation energies, (3) TDDFT and CIS yield similar estimates of the dipole moment change between the S0 and S1 states, both of which are in the range of previous experimental estimates, (4) in each case, the S2 state is at least 0.5 eV above the S1 state for the ground-state geometry, and (5) proton transfer is not likely in the ground state of C343 but is only 0.18 eV higher in energy in the S1 state. We also compare the DFT/TDDFT results with RHF/CIS, MP2, and INDO S/CI results. We find good agreement between MP2 and experimental ground-state dipole moments and good agreement between INDO S/CI and TDDFT gas-phase excitation energies

The mechanical behavior of cross-rolled beryllium sheet

In response to the failure of a conical section of the Insat C satellite during certification testing, the use of beryllium for payload structures, particularly in sheet product form, is being reevaluated. A test program was initiated to study the tensile, shear, and out-of-plane failure modes of beryllium cross-rolled sheet and to apply data to the development of an appropriate failure criterion. Tensile test results indicated that sanding the surface of beryllium sheet has no significant effect on yield strength but can produce a profound reduction in ultimate strength and results obtained by finite element analysis. Critical examination of these test results may contribute to the modification of a JSC policy for the use of beryllium in orbiter and payload structures

Theoretical Investigation of the Ground and Excited States of Coumarin 151 and Coumarin 120

We present calculations of various properties of the ground and excited states of Coumarins 151 and 120. These and related coumarins are important in investigating ultrafast solvation processes in liquids and complex solutions as well as being important acceptors in model electron-transfer systems. We calculate the following:  (1) the electronic excitation energies to several low-lying singlet states, (2) ground and excited-state dipole moments, (3) solvation effects on excitation energies, and (4) the properties of single Coumarin 151-water complexes. We test our Time-Dependent Density Functional Theory (TDDFT) calculations against CASSCF, CASPT2 (both single and multistate versions), CIS, and ZINDO. Using TDDFT, we find excellent agreement with experimental S1 ← S0 excitation energies. On the basis of these results, we address several outstanding questions for these systems and find:  (1) that TICT-formation is unlikely upon photexcitation for gas-phase C151, (2) a greater tendency toward a planar amine group for the S1 state than for the ground state, (3) significant differences between our gas-phase ground-state dipole moment and the experimental value, and (4) TDDFT results for water−Coumarin 151 complexes are in good agreement with the experimental results of Topp and co-workers

Solvent as Electron Donor: Donor/Acceptor Electronic Coupling Is a Dynamical Variable

We combine analysis of measurements by femtosecond optical spectroscopy, computer simulations, and the generalized Mulliken−Hush (GMH) theory in the study of electron-transfer reactions and electron donor−acceptor interactions. Our focus is on ultrafast photoinduced electron-transfer reactions from aromatic amine solvent donors to excited-state acceptors. The experimental results from femtosecond dynamical measurements fall into three categories:  six coumarin acceptors reductively quenched by N,N-dimethylaniline (DMA), eight electron-donating amine solvents reductively quenching coumarin 152 (7-(dimethylamino)-4-(trifluoromethyl)coumarin), and reductive quenching dynamics of two coumarins by DMA as a function of dilution in the nonreactive solvents toluene and chlorobenzene. Applying a combination of molecular dynamics trajectories, semiempirical quantum mechanical calculations (of the relevant adiabatic electronic states), and GMH theory to the C152/DMA photoreaction, we calculate the electron donor/acceptor interaction parameter HDA at various time frames. HDA is strongly modulated by both inner-sphere and outer-sphere nuclear dynamics, leading us to conclude that HDA must be considered as a dynamical variable

Numerical Simulations of a Quiet SuperSonic Technology (QueSST) Aircraft Preliminary Design

Reynolds Averaged Navier-Stokes (RANS) simulations were performed on a Lockheed Martin Quiet SuperSonic Technology (QueSST) aircraft preliminary design to assess inlet performance. The FUN3D flow solver and its adjoint-based grid refinement capability were used for the simulations in hopes of determining internal "best practices" for predicting inlet performance on top-aft-mounted inlets. Several parameters were explored including tetrahedral vs. pentahedral cells in/around the boundary-layer regions, an engine axis-aligned linear pressure sensor vs. a pressure box objective as the grid adaptation metric, and the number of grid adaptation cycles performed. Additional simulations were performed on manually refined grids for comparison with the adjoint-based adapted grids. Results showed poor agreement in predicted inlet performance on the refined grids compared to experimental data. This was true regardless of whether the refinement was adjoint-based or manual, the cell type in/near the boundary-layer regions, or the grid adaptation metric used. In addition, the 40-probe total pressure recovery was shown to decrease asymptotically as the number of adaptation cycles is increased. Solutions on the unadapted grids generally had better agreement with experimental data than their refined grid counterparts

Numerical Simulations of a Quiet SuperSonic Technology (QueSST) Aircraft Preliminary Design

Reynolds Averaged Navier-Stokes (RANS) simulations were performed on the Lockheed Martin Quiet SuperSonic Technology (QueSST) aircraft preliminary design to assess inlet performance. The FUN3D flow solver and its adjoint-based grid refinement capability was used for the simulations in hopes of determining internal "best practices" for predicting inlet performance on top-aft-mounted inlets. Several parameters were explored including tetrahedral vs. pentahedral cells in/around the boundary-layer regions, an engine axis-aligned linear pressure sensor vs. a pressure box objective as the grid adaptation metric, and the number of grid adaptation cycles performed. Additional simulations were performed on manually refined grids for comparison with the adjoint-based adapted grid

Design guide for high pressure oxygen systems

A repository for critical and important detailed design data and information, hitherto unpublished, along with significant data on oxygen reactivity phenomena with metallic and nonmetallic materials in moderate to very high pressure environments is documented. This data and information provide a ready and easy to use reference for the guidance of designers of propulsion, power, and life support systems for use in space flight. The document is also applicable to designs for industrial and civilian uses of high pressure oxygen systems. The information presented herein are derived from data and design practices involving oxygen usage at pressures ranging from about 20 psia to 8000 psia equal with thermal conditions ranging from room temperatures up to 500 F

CFD Models of a Serpentine Inlet, Fan, and Nozzle

Several computational fluid dynamics (CFD) codes were used to analyze the Versatile Integrated Inlet Propulsion Aerodynamics Rig (VIIPAR) located at NASA Glenn Research Center. The rig consists of a serpentine inlet, a rake assembly, inlet guide vanes, a 12-in. diameter tip-turbine driven fan stage, exit rakes or probes, and an exhaust nozzle with a translating centerbody. The analyses were done to develop computational capabilities for modeling inlet/fan interaction and to help interpret experimental data. Three-dimensional Reynolds averaged Navier-Stokes (RANS) calculations of the fan stage were used to predict the operating line of the stage, the effects of leakage from the turbine stream, and the effects of inlet guide vane (IGV) setting angle. Coupled axisymmetric calculations of a bellmouth, fan, and nozzle were used to develop techniques for coupling codes together and to investigate possible effects of the nozzle on the fan. RANS calculations of the serpentine inlet were coupled to Euler calculations of the fan to investigate the complete inlet/fan system. Computed wall static pressures along the inlet centerline agreed reasonably well with experimental data but computed total pressures at the aerodynamic interface plane (AIP) showed significant differences from the data. Inlet distortion was shown to reduce the fan corrected flow and pressure ratio, and was not completely eliminated by passage through the fa

Assembly and structure of α-helical peptide films on hydrophobic fluorocarbon surfaces

The structure, orientation and formation of amphiphilic α-helix model peptide films on fluorocarbon surfaces has been monitored with sum frequency generation (SFG) vibrational spectroscopy, near edge X-ray absorption fine structure (NEXAFS) spectroscopy and X-ray photoelectron spectroscopy (XPS). The α-helix peptide is a 14-mer of hydrophilic lysine and hydrophobic leucine residues with a hydrophobic periodicity of 3.5. This periodicity yields a rigid amphiphilic peptide with leucine and lysine side chains located on opposite sides. XPS composition analysis confirms the formation of a peptide film that covers about 75% of the surface. NEXAFS data are consistent with chemically intact adsorption of the peptides. A weak linear dichroism of the amide π* is likely due to the broad distribution of amide bond orientations inherent to the α-helical secondary structure. SFG spectra exhibit strong peaks near 2865 cm(−1) and 2935 cm(−1) related to aligned leucine side chains interacting with the hydrophobic surface. Water modes near 3200 cm(−1) and 3400 cm(−1) indicate ordering of water molecules in the adsorbed--peptide fluorocarbon surface interfacial region. Amide I peaks observed near 1655 cm(−1) confirm that the secondary structure is preserved in the adsorbed peptide. A kinetic study of the film formation process using XPS and SFG showed rapid adsorption of the peptides followed by a longer assembly process. Peptide SFG spectra taken at the air–buffer interface showed features related to well ordered peptide films. Moving samples through the buffer surface led to the transfer of ordered peptide films onto the substrates