Engineering topics

Stancil, P. C.

Publications and source records attributed to Stancil, P. C..

8 records

DOE OSTI2024

Inelastic Triatom-Atom Quantum Close-Coupling Dynamics in Full Dimensionality: All Rovibrational Mode Quenching of Water Due to the H Impact on a Six-Dimensional Potential Energy Surface

The rovibrational level populations, and subsequent emission in various astrophysical environments, are driven by inelastic collision processes. The available rovibrational rate coefficients for water have been calculated using a number of approximations. We present a numerically exact calculation for the rovibrational quenching for all water vibrational modes due to collisions with atomic hydrogen. The scattering theory implements a quantum close-coupling (CC) method on a high level ab initio six-dimensional (6D) potential energy surface (PES). Total rovibrational quenching cross sections for excited bending levels were compared with earlier results on a 4D PES with the rigid-bender closecoupling (RBCC) approximation. General agreement between 6D-CC and 4DRBCC calculations are found, but differences are evident including the energy and amplitude of low-energy orbiting resonances. Quenching cross sections from the symmetric and asymmetric stretch modes are provided for the first time. The current 6D-CC calculation provides accurate inelastic data needed for astrophysical modeling.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2021

Inelastic, exchange, and reactive processes in rovibrationally excited collisions of HD with H

ABSTRACT The HD molecule is an important coolant in early universe chemistry models and a tracer of H2 in star-forming regions. Rate coefficients for collisional excitation and de-excitation of HD rotational and vibrational levels form important ingredients in astrophysical models. While collisions with He, H2, and H are the most important, available data for H + HD collisions are largely limited to temperatures less than 1000 K for the vibrational ground state, low-lying rotational levels of the v = 1 HD vibrational level, or computed without reactive contributions. Here, through explicit quantum scattering calculations, we report extensive data for rovibrational transitions in HD induced by H atoms for a range of rotational levels in v = 1 and some v = 0 levels for temperatures up to 1000 K. The significance of the computed results for astrophysical modeling is discussed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2020

Panning for Gold: New Emission Lines from UV–VIS Spectroscopy of Au i and Au ii

The recent detection of a neutron star merger by the LIGO collaboration has renewed interest in laboratory studies of r-process elements. Accurate modeling and interpretation of the electromagnetic transients following the mergers requires computationally expensive calculations of both the structure and opacity of all trans-iron elements. To date, the necessary atomic data to benchmark structure codes are incomplete or, in some cases, absent entirely. Within the available laboratory studies, the literature on Au i and Au ii provides incomplete reports of the emission lines and level structures. We present a new study of Au i and Au ii lines and levels by exposing a solid gold target to plasma in the Compact Toroidal Hybrid (CTH) experiment at Auburn University. A wavelength range from 187 to 800 nm was studied. In Au i, 86 lines are observed, 43 of which are unreported in the literature, and the energies of 18 $5{d}^{9}6s6p$ levels and 16 of the 18 known $5{d}^{9}6s6d$ levels are corroborated by a least-squares level energy optimization. In Au ii, 76 emission lines are observed, and 51 of the lines are unreported in the literature. For both Au i and Au ii, the new lines predominantly originate from the most energetic of the known levels, and over half of the new Au ii lines have wavelengths longer than 300 nm. For the estimated electron parameters of CTH plasmas at the gold target (ne ~ 10 12 cm -3 , T e ~ 10 eV), two-electron transitions are similar in intensity to LS-allowed one-electron transitions.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS2006

Quenching of Excited Na due to He Collisions

The quenching and elastic scattering of excited Sodium by collisions with Helium have been investigated for energies between 10(exp -13) eV and 10 eV. With the ab initio adiabatic potentials and nonadiabatic radial and rotational couplings obtained from multireference single- and double-excitation configuration interaction approach, we carried out scattering calculations by the quantum-mechanical molecular-orbital close-coupling method. Cross sections for quenching reactions and elastic collisions are presented. Quenching and elastic collisional rate coefficients as a function of temperature between 1 micro-K and 10,000 K are also obtained. The results are relevant to modeling non-LTE effects on Na D absorption lines in extrasolar planets and brown dwarfs.

Lin, C. Y.↗

NASA NTRS2006

Vibrational and rotational quenching of CO by collisions with H, He, and H2

Collisional quenching of molecular species is an important process in a variety of astrophysical environments including interstellar clouds, photodissociation regions, and cool stellar/planetary atmospheres. In this work, quantum mechanical scattering calculations are presented for the rotational and vibrational relaxation of rotationally-excited CO due to collisions with H, He and H2 for collision energies between 10(exp -6) and approx.15000/cm. The calculations were performed using the close-coupling approach and the l-labeled form of the coupled-states approximation. Cross sections and rate coefficients for the quenching of the v=0-2, j=0-6 levels of CO are presented and comparisons with previous calculations and measurements, where available, are provided.

Yang, Benhui↗

NASA NTRS2002

Laboratory Measurements of Charge Transfer on Atomic Hydrogen at Thermal Energies

We describe our ongoing program to measure velocity dependent charge transfer (CT) cross sections for selected ions on atomic hydrogen using the ion-aloin merged-beams apparatus at Oak Ridge Natioiial Laboralory. Our focus is on those ions for which CT plays an important role in determining the ionization structure, line emis sion, and thermal structure of observed cosmic photoionized plasmas.

Havener, C. C.↗

NASA NTRS2002

Charge Transfer Calculations and Database for Astrophysics

A variety of theoretical approaches, having different but overlapping energy ranges of applicability, are applied to investigate charge transfer processes for collisions of atomic ions with atoms and molecules. The methods include quantal molecular-orbital close-coupling, classical trajectory Monte Carlo, and continuum distorted wave methods. Recent collision systems studied include S(+4) + H, S(+4) + He, N(+7) + He, H2O, CO, and CO2, O(+q)(q = 1 - 8) + H, H2, and S(+q)(q = 1 - 16) + H2. The database effort is concentrating on astrophysically important reactions of atomic ions X(+q)(X=H-Zn, q=1-4, and selected higher charges) with H, He, various metal atoms, H2, and other selected molecular targets. Existing data, much of it produced by us, has been compiled and critically evaluated. Data for many reactions missing in the literature are estimated using the multichannel Landau-Zener approximation. Fits to cross sections and rate coefficients using standard functions are provided as well as tabulations of the raw data. The database is available on the World Wide Web at cfadc.phy.ornl.gov/astro/ps/data.

Wang, J. G.↗

NASA NTRS2002

Molecular Line and Continuum Opacities for Modeling of Extrasolar Giant Planet and Cool Stellar Atmospheres

The molecular line and continuum opacities are investigated in the atmospheres of cool stars and Extrasolar Giant Planets (EGPs). Using a combination of ab inito and experimentally derived potential curves and dipole transition moments, accurate data have been calculated for rovibrationally-resolved oscillator strengths and photodissociation cross sections in the B' (sup 2)Sigma+ (left arrow) X (sup 2)Sigma+ and A (sup 2)Pi (left arrow) X (sup 2)Sigma+ band systems in MgH. We also report our progress on the study of the electronic structure of LiCl and FeH.

Weck, P. F.↗