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Computer program for line-by-line calculation of spectra from diatomic molecules and atoms assuming Voigt line profile
Sudden approximation applied to rotational transition probabilities and inelastic total cross sections for scattering of homonuclear diatomic molecules by atoms
The ab initio theoretical treatment of one-photon double photoionization processes has been limited to atoms and diatomic molecules by the challenges posed by large grid-based representations of the double ionized continuum wave function. To provide a path for extensions to polyatomics, an energy-adapted orbital basis approach is demonstrated that reduces the dimensions of such representations and simultaneously allows larger time steps in time-dependent computational descriptions of double ionization. Additionally, an algorithm that exploits the diagonal nature of the two-electron integrals in the grid basis and dramatically accelerates the transformation between grid and orbital representations is presented. Excellent agreement between the present results and benchmark theoretical calculations is found for H – and Be atoms, as well as the hydrogen molecule, including for the triply differential cross sections that relate the angular distribution and energy sharing of all of the particles in the molecular frame.
The C10H8(+) cation and its dehydrogenated derivatives, C10H7(+) and C10H6(+), have been studied using a selected ion flow tube (SIFT). Reactions with molecules and atoms of interstellar interest show that C10H8(+) reacts with N md O to give neutral products HCN and CO, respectively. C10H6(+) and C10H6(+) are moderately reactive and reactions proceed through association with molecules. The implications of these results for the depletion of C10H(n)(+) in the interstellar medium are briefly discussed.
Diatomic polar molecule rotational excitation by atomic impact to obtain transition cross section angular distribution and energy dependence
Rotational and vibrational transitions in a diatomic molecule caused by collisions with an atom are analyzed by a semiclassical method for conditions where the rotational transitions can be handled well by the sudden approximation and the vibrational transitions belong to the adiabatic regime. The contribution to the vibrational transition probability from the correction, which takes the finite value of the spacing between rotational energy levels into account, is examined.-
Preliminary results of a research program to determine energy partitioning in spacecraft thermal protection materials due to atom recombination at the gas-surface interface are presented. The primary focus of the research is to understand the catalytic processes which determine heat loading on Shuttle, Aeroassisted OTV, and NASP thermal protection surfaces in nonequilibrium flight regimes. Highly sensitive laser diagnostics based on laser-induced fluorescence and resonantly-enhanced multiphoton ionization spectroscopy are used to detect atoms and metastable molecules. At low temperatures, a discharge flow reactor is employed to measure deactivation/recombination coefficients for O-atoms, N-atoms, and O2. Detection methods are presented for measuring O-atoms, O2 and N2, and results for deactivation of O2 and O-atoms on reaction-cured glass and Ni surfaces. Both atom recombination and metastable product formation are examined. Radio-frequency discharges are used to produce highly dissociated beams of atomic species at energies characteristic of the surface temperature. Auger electron spectroscopy is employed as a diagnostic of surface composition in order to accurately define and control measurement conditions.
Charge exchange followed by radiative stabilization are the main processes responsible for the recent observations of X-ray emission from comets in their approach to the Sun. A new apparatus was constructed to measure, in collisions of HCIs with atoms and molecules, (a) absolute cross sections for single and multiple charge exchange, and (b) normalized X-ray emission cross sections.
Over the last 20 years, XUV and X-ray free-electron lasers have enabled a wide variety of time-resolved experiments that have dramatically advanced our understanding of ultra-fast molecular dynamics on atomic length scales and femto-second time scales. This review focuses on experimental studies of ultrafast dynamics of atoms and molecules in the gas phase, tracing the development of the field from early proof-of-principle studies to recent pump-probe experiments that elucidate the coupled electronic and nuclear dynamics during photochemical reactions with a temporal resolution that is now extending into the attosecond domain.
The impact parameter method and the sudden approximation are applied to determine the total probability of inelastic rotational transitions arising from a collision of an atom and a homonuclear diatomic molecule at large impact parameters. An analytical approximation to this probability is found for conditions where the electron exchange or overlap forces dominate the scattering. An approximate upper bound to the range of impact parameters for which rotational scattering can be important is determined. In addition, an estimate of the total inelastic cross section is found at conditions for which a statistical model describes the scattering well. The results of this analysis are applied to Ar-O2 collisions and may be readily applied to other combinations of atoms and molecules.
Upper and lower bounds for Thomas-Fermi energies of atoms and homonuclear diatomic molecules at large and intermediate internuclear separations, noting instability
In atom probe tomography of molecular organic materials, field ionization of either entire molecules or molecular fragments can occur, but the mechanism governing this behavior was not previously understood. This work explains when a doubly ionized small molecule organic material is expected to undergo fragmentation. Here, we find that multiple detection events arising from post-ionization fragmentation of a parent molecular dication into two daughter ions is well explained by the free energy and geometries of the molecules computed using density functional theory. Of the systems studied, exergonic free energies for formation of the daughter ions, smaller activation energies for dissociation, and increases in bond length are all found to be quantitative predictors for ion fragmentation. This work expands the applicability of atom probe tomography to organic materials by increasing the fundamental understanding of processes occurring during this analysis technique.
(Ir)2InIn11Ga4O15 crystallizes in the orthorhombic Pnn2 space group. The structure is three-dimensional and consists of two indium, elemental molecules; four iridium atom molecules; and one In11Ga4O15 framework. In the In11Ga4O15 framework, there are six inequivalent In1+ sites. In the first In1+ site, In1+ is bonded in a 4-coordinate geometry to four O2- atoms. There are a spread of In–O bond distances ranging from 2.23–2.45 Å. In the second In1+ site, In1+ is bonded in a 4-coordinate geometry to four O2- atoms. There are a spread of In–O bond distances ranging from 2.18–2.40 Å. In the third In1+ site, In1+ is bonded in a 4-coordinate geometry to four O2- atoms. There are a spread of In–O bond distances ranging from 2.12–2.42 Å. In the fourth In1+ site, In1+ is bonded in a 3-coordinate geometry to three O2- atoms. There are a spread of In–O bond distances ranging from 2.13–2.31 Å. In the fifth In1+ site, In1+ is bonded in a 3-coordinate geometry to three O2- atoms. There are one shorter (2.14 Å) and two longer (2.23 Å) In–O bond lengths. In the sixth In1+ site, In1+ is bonded in a distorted L-shaped geometry to two equivalent O2- atoms. Both In–O bond lengths are 2.97 Å. There are two inequivalent Ga3+ sites. In the first Ga3+ site, Ga3+ is bonded in a tetrahedral geometry to four O2- atoms. There are a spread of Ga–O bond distances ranging from 1.86–1.94 Å. In the second Ga3+ site, Ga3+ is bonded to four O2- atoms to form distorted corner-sharing GaO4 tetrahedra. There are a spread of Ga–O bond distances ranging from 1.83–1.90 Å. There are eight inequivalent O2- sites. In the first O2- site, O2- is bonded in a bent 150 degrees geometry to two equivalent Ga3+ atoms. In the second O2- site, O2- is bonded in a 4-coordinate geometry to three In1+ and one Ga3+ atom. In the third O2- site, O2- is bonded to three In1+ and one Ga3+ atom to form corner-sharing OIn3Ga tetrahedra. In the fourth O2- site, O2- is bonded to three In1+ and one Ga3+ atom to form corner-sharing OIn3Ga tetrahedra. In the fifth O2- site, O2- is bonded in a 3-coordinate geometry to two In1+ and one Ga3+ atom. In the sixth O2- site, O2- is bonded in a 4-coordinate geometry to three In1+ and one Ga3+ atom. In the seventh O2- site, O2- is bonded in a trigonal non-coplanar geometry to three In1+ and one Ga3+ atom. In the eighth O2- site, O2- is bonded in a trigonal non-coplanar geometry to two In1+ and one Ga3+ atom.
S-matrix computations for quantum transitions, considering close coupling case of homonuclear diatomic molecular rotational excitation
Recent calculations of the viscosity of iodine suggest that existing predictions of viscosities of high-temperature (up to several thousands degrees) gases should be revised, with much more attention being paid to the atomic and molecular interactions in the gas. As the gas starts to dissociate, the frequency of atom-molecule and atom-atom interactions increases, and those collisions must be taken into account in calculations of viscosity at high temperature. In this study, the iodine is chosen as an example, and the dependence of its viscosity on the gas dissociation degree is shown. Several possible channels for I+I interaction are considered in addition to I+I2 and I2+I2 collisions, and the resulting collision integrals are averaged over all the important channels.
Fast Ar beams have been scattered by room-temperature CO2, OCS, and CS2 to obtain average atom-molecule potentials. The results are consistent with other scattering measurements on similar systems, and are also in excellent agreement with available theoretical calculations based on an electron-gas model. Decomposition of the atom-molecule potentials into constituent atom-atom potentials shows that such a representation can be utilized with fair accuracy but that a definite discrepancy exists.
Compound state resonances in atom/molecule collisions below first excitation threshold energy
In new apparatus, most of electrons scattered inelastically over wide range of angles measured simultaneously, with consequent increase in signal-to-noise ratio by factor of about 10 to 4th power. Beam of electrons and beam of ions aimed along low-intensity magnetic field between pair of electric-field plates. Crossed electric and magnetic fields hardly affect ions but cause electrons to drift toward ions by trochoidal motion. With modifications, apparatus used for measurements of excitation cross sections in neutral atoms, molecules, radicals, and excited states of atoms and molecules.