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DOE OSTI2025

Increased Ly α Opacity in White Dwarf Photospheres from Transient H − Resonances

The structure and emergent flux of hydrogen atmosphere white dwarfs depend on the opacity of the Lyα and Lyβ spectral lines. The opacity here is set by the strength and broadening of these lines; the latter is dictated by the far line wing, which is in the “quasi-static” limit of electron broadening, placing it in the incomplete collision regime, and describes the transient parts of electron and ion collisions. These transient stages of the collision form resonances: In the case of ions, they manifest as molecular resonances, while for electrons they are H − resonances, both of which can only be captured quantum-mechanically. Quantum-mechanical calculations have historically preserved only a handful of broadening terms that are most important near the center of the line. However, in the wings of the line, the previously neglected terms that describe the transient stages of the collision need to be included. This requirement arises because, in the line wings, the broadening from the 1s ground state, which is generally assumed to be extremely small compared to the broadening of the upper state, is no longer negligible within a quantum-mechanical model that takes into account exchange interactions. The inclusion of all the transient terms results in asymmetries and extra broadening. The increased broadening of Lyα increases the opacity at the energy where most of the flux leaves the star. The broader Lyα lines also impact the visible flux, raising it by an amount that exceeds previously estimated errors.

74 ATOMIC AND MOLECULAR PHYSICS↗

DOE OSTI2024

Analysis and Grading of the Test Performance of PS Modules for the CMS Phase-II Outer Tracker Upgrade

The Outer Tracker detector of the Compact Muon Solenoid (CMS) experiment provides information about the trajectory of charged particles produced in proton-proton collisions at the Large Hadron Collider (LHC). During the High Luminosity LHC upgrade, scheduled for the late 2020s, the Outer Tracker will be replaced with new modules capable of transmitting data to the L1 Trigger. These modules are being assembled at several facilities around the world, including Fermilab, necessitating coordinated standards of module quality. Here I discuss the development of POTATO (Phase-II Outer Tracker Analyzer of Test Outputs), a C++ software which provides a standardized procedure for analyzing and grading test results of the Outer Tracker modules. The particular focus of this paper is on the analysis and grading of the PS (pixel-strip) modules in POTATO.

43 PARTICLE ACCELERATORS↗

DOE OSTI2020

Higgs boson pair production via gluon fusion at N 3 LO in QCD

We present next-to-next-to-next-to-leading order ( N 3 LO ) QCD predictions for the Higgs boson pair production via gluon fusion at hadron colliders in the infinite top-quark mass limit. Besides the inclusive total cross sections at various collision energies, we also provide the invariant mass distribution of the Higgs boson pair. Our results show that the N 3 LO QCD corrections enhance the next-to-next-to-leading order cross section by 3.0% (2.7%) at s = 13 ( 100 ) TeV , while the scale uncertainty is reduced substantially below 3% (2%). We also find that a judicious scale choice can significantly improve the perturbative convergence. For the invariant mass distribution, our calculation demonstrates that the N 3 LO corrections improve the scale dependence but almost do not change the shape.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2021

Ab initio electron dynamics in high electric fields: Accurate prediction of velocity-field curves

Electron dynamics in external electric fields governs the behavior of solid-state electronic devices. First-principles calculations enable precise predictions of charge transport in low electric fields. However, studies of high-field electron dynamics remain elusive due to a lack of accurate and broadly applicable methods. In this work, we develop an efficient approach to solve the real-time Boltzmann transport equation with both the electric field term and ab initio electron-phonon collisions. These simulations provide field-dependent electronic distributions in the time domain, allowing us to investigate both transient and steady-state transport in electric fields ranging from low to high (> 10 kV/cm). The broad capabilities of our approach are shown by computing nonequilibrium electron occupations and velocity-field curves in Si, GaAs, and graphene, obtaining results in quantitative agreement with experiment. Our approach sheds light on microscopic details of transport in high electric fields, including the dominant scattering mechanisms and valley occupation dynamics. Our results demonstrate quantitatively accurate calculations of electron dynamics in low to high electric fields, with broad application to power and micro-electronics, optoelectronics, and sensing.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2023

Spectroscopic Investigations of Molecular Symmetry Breakdown

This project addressed precise measurements of the spectra of molecules to address fundamental questions in chemical physics in the realm of nuclear spin symmetries and their breakdown in molecules, and parity non-conservation caused by the weak nuclear force. Nuclear spin symmetry is intimately connected to parity in symmetrical molecules and plays a central role in the physical and chemical properties of symmetric molecules, their collisional relaxation, and the establishment of thermodynamic equilibrium in an ensemble. Such effects are present in every molecular system or process, but their small size means they are often only directly observable under special conditions. However, their measurement is of fundamental, and often practical importance, and strongly relates to the themes of coherence in light and matter in the recent Basic Energy Sciences Advisory Committee (BESAC) report “Challenges at the Frontiers of Matter and Energy: Transformative Opportunities for Discovery Science”. We begin by addressing lifetime broadening of spectroscopic lines caused by self-collisions in acetylene, where efficient resonant rotational energy transfer between a pair of molecules separated in energy by rotational quantum number ΔJ = ± 2, can result in a different pressure broadening for ortho- and para- nuclear spin state molecules. This work was prompted by a controversial report [Iwakuni et al. Phys. Rev Letts. 117 (2016) 143902] of the observation of such an effect in the v 1 +v 3 combination band transition of acetylene discussed in the original proposal. After delays caused by the COVID-19 pandemic, we have completed these measurements and a paper was published in the Journal of Chemical Physics describing the work. The measurements pointed out that the use of an approximate model in the analysis of the original work was the cause of the erroneous conclusion that ortho and para acetylene molecules had substantially different collisional lifetime broadening. In the process, much improved broadening measurements have been made that will permit more reliable modeling of the effects in the future. Subsequently, we have completed a new set of measurements of self- and nitrogen-collisional broadening at a series of low and intermediate temperatures to characterize the temperature dependence of the effects in the molecule. This work is currently being analyzed and will be the subject of a paper to be published in the relatively near future. In addition, some very preliminary measurements of CH 4 as described in the proposal, have been completed. If facilities and time permit, these will continue as an undergraduate research project.

74 ATOMIC AND MOLECULAR PHYSICS↗

NASA NTRS1994

A multi-ion generalized transport model of the polar wind

The higher-order generalizations of the equations of standard hydrodynamics, known collectively as generalized transport theories, have been used since the early 1980s to describe the terrestrial polar wind. Inherent in the structure of generalized transport theories is the ability to describe not only interparticle collisions but also certain non-Maxwellian processes, such as heat flow and viscous stress, that are characteristic of any plasma flow that is not collision dominated. Because the polar wind exhibits a transition from collision-dominated to collisionless flow, generalized transport theories possess advantages for polar wind modeling not shared by either collision-dominated models (such as standard hydrodynamics) or collisionless models (such as those based on solving the collisionless Boltzmann equation). In general, previous polar wind models have used generalized transport equations to describe electrons and only one species of ion (H(+)). If other ion species were included in the models at all, it was in a simplified or semiempirical manner. The model described in this paper is the first polar wind model that uses a generalized transport theory (bi-Maxwellian-based 16-moment theory) to describe all of the species, both major and minor, in the polar wind plasma. In the model, electrons and three ion species (H(+), He(+), O(+)) are assumed to be major and several ion species are assumed to be minor (NO(+), Fe(+), O(++)). For all species, a complete 16-moment transport formulation is used, so that profiles of density, drift velocity, parallel and perpendicular temperatures, and the field-aligned parallel and perpendicular energy flows are obtained. In the results presented here, emphasis is placed on describing those constituents of the polar wind that have received little attention in past studies. In particular, characteristic solutions are presented for supersonic H(+) outflow and for both supersonic and subsonic outflows of the major ion He(+). Solutions are also presented for various minor ions, both atomic and molecular and both singly and multiply charged.

Demars, H. G.↗

DOE OSTI2022

Measurements of atoms and metastable species in N 2 and H 2 –N 2 nanosecond pulse plasmas

We report time-resolved, absolute number densities of metastable N 2 (A 3 Σ u + , v = 0, 1) molecules, ground state N 2 and H atoms, and rotational–translational temperature have been measured by tunable diode laser absorption spectroscopy and two-photon absorption laser-induced fluorescence in diffuse N 2 and N 2 –H 2 plasmas during and after a nanosecond pulse discharge burst. Comparison of the measurement results with the kinetic modeling predictions, specifically the significant reduction of the N 2 (A 3 Σ u + ) populations and the rate of N atom generation during the burst, suggests that these two trends are related. The slow N atom decay in the afterglow, on a time scale longer than the discharge burst, demonstrates that the latter trend is not affected by N atom recombination, diffusion to the walls, or convection with the flow. This leads to the conclusion that the energy pooling in collisions of N 2 (A 3 Σ u + ) molecules is a major channel of N 2 dissociation in electric discharges where a significant fraction of the input energy goes to electronic excitation of N 2 . Additional measurements in a 1% H 2 –N 2 mixture demonstrate a further significant reduction of N 2 (A 3 Σ u + , v = 0, 1) populations, due to the rapid quenching by H atoms accumulating in the plasma. Comparison with the modeling predictions suggests that the N 2 (A 3 Σ u + ) molecules may be initially formed in the highly vibrationally excited states. The reduction of the N 2 (A 3 Σ u + ) number density also diminishes the contribution of the energy pooling process into N2 dissociation, thus reducing the N atom number density. The rate of N atom generation during the burst also decreases, due to its strong coupling to N 2 (A 3 Σ u + , v) populations. On the other hand, the rate of H atom generation, produced predominantly by the dissociative quenching of the excited electronic states of N 2 by H 2 , remains about the same during the burst, resulting in a nearly linear rise in the H atom number density. Comparison of the kinetic model predictions with the experimental results suggests that the yield of H atoms during the quenching of the excited electronic state of N 2 by molecular H 2 is significantly less than 100%. The present results quantify the yield of N and H atoms in high-pressure H 2 –N 2 plasmas, which have significant potential for ammonia generation using plasma-assisted catalysis

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2022

Breakdown of the single-collision condition for soft x-ray high harmonic generation in noble gases

High harmonic generation (HHG) in atomic gases is generally assumed to originate from photoelectrons that are not perturbed by neighboring particles. In this paper, we study theoretically and experimentally the regime where this approximation breaks down. At high laser intensities, we experimentally find that producing soft x-rays beyond this single-collision condition leads to a strong reduction of the coherent HHG response and appearance of incoherent radiation. We generalize our results to phase-matched HHG with mid-infrared drivers, and determine that a minimum pulse energy is needed to simultaneously phase match the HHG process and keep photoelectrons unperturbed by surrounding particles. Therefore, while previous research showed that HHG efficiency is independent of the driving pulse energy if other experimental parameters are scaled accordingly, we find that this rule no longer applies for high photon energies. Our study thus provides important guidelines for the laser parameters needed for the generation of high flux soft x-ray high harmonics.

74 ATOMIC AND MOLECULAR PHYSICS↗

DOE OSTI2020

Double differential distributions of e-emission in ionization of N 2 by 3,4 and 5 keV electron impact

In this paper, we report the measurement of the absolute double differential cross sections (DDCS) of secondary electrons emitted due to the ionization of N2 molecule in collisions with fast electrons having energies between 3 and 5 keV. The emitted electrons with energies from 1-500 eV have been measured for different forward and backward emission angles. The measured DDCS have been compared with the state-of-the-art first Born approximation with correct boundary condition (CB1) model calculations as well as with the classical trajectory Monte Carlo (CTMC) method. From the measured DDCS, the single differential cross sections (SDCS) as a function of the emission energies have been computed and eventually the total ionization cross sections (TCS) have been derived. The TCS values are also compared with a semi-empirical calculation, namely, the CSP-ic (complex scattering potential-ionization contribution) model.

74 ATOMIC AND MOLECULAR PHYSICS↗

DOE OSTI2020

On the nonadiabatic collisional quenching of OH(A) by H 2 : a four coupled quasi-diabatic state description

A four-state diabatic potential energy matrix (DPEM), H d , for the description of the nonadiabatic quenching of OH(A 2 Σ + ) by collisions with H 2 is reported. The DPEM is constructed as a fit to adiabatic energies, energy gradients, and derivative couplings obtained exclusively from multireference configuration interaction wave functions. A four-adiabatic-electronic-state representation is used in order to describe all energetically accessible regions of the nuclear coordinate space. Partial permutation-inversion symmetry is incorporated into the representation. Here, the fit is based on electronic structure data at 42 882 points, described by over 1.6 million least squares equations with a root mean square (mean unsigned) error of 178(83) cm –1 . Comparison of ab initio and H d determined minima, saddle points, and energy minimized points on C 2v , C s , C ∞v , and C 1 (noncoplanar) portions of two conical intersection seams are used to establish the accuracy of the H d .

74 ATOMIC AND MOLECULAR PHYSICS↗

DOE OSTI2021

Complete collision data set for electrons scattering on molecular hydrogen and its isotopologues: II. Fully vibrationally-resolved electronic excitation of the isotopologues of H 2 (X 1 $Σ^{+}_{g}$)

Here, we present a comprehensive set of vibrationally-resolved cross sections for electron-impact electronic excitation of the isotopologues of molecular hydrogen (D 2 , T 2 , HD, HT, and DT) initially in the ground electronic state. We apply the adiabatic-nuclei molecular convergent close-coupling (MCCC) method to calculate cross sections from threshold to 500 eV for excitation of all bound vibrational levels and dissociative excitation of the B 1 $Σ^{+}_{g}$, C 1 Π u , EF 1 $Σ^{+}_{g}$, B' 1 $Σ^{+}_{g}$, GK 1 $Σ^{+}_{g}$, I 1 Π g , J 1 Δ g , D 1 Π u , H 1 $Σ^{+}_{g}$, b 1 $Σ^{+}_{g}$, c 3 Π u , a 3 $Σ^{+}_{g}$, e 3 $Σ^{+}_{u}$, d 3 Π u , h 3 $Σ^{+}_{g}$, g 3 $Σ^{+}_{g}$, i 3 Π g , and j 3 Δ g electronic states from all bound vibrational levels of the ground electronic (X 1 $Σ^{+}_{g}$) state. Including the previously-published MCCC e-H2 cross sections the data set contains cross sections for over 60,000 electronic and vibrational transitions. The cross sections are presented in graphical form and provided as both numerical values and analytic fit functions in supplementary data files. The data can also be downloaded from the MCCC database at mccc-db.org.

74 ATOMIC AND MOLECULAR PHYSICS↗

NASA NTRS1996

Molecular Dynamics Calculations

The development of thermodynamics and statistical mechanics is very important in the history of physics, and it underlines the difficulty in dealing with systems involving many bodies, even if those bodies are identical. Macroscopic systems of atoms typically contain so many particles that it would be virtually impossible to follow the behavior of all of the particles involved. Therefore, the behavior of a complete system can only be described or predicted in statistical ways. Under a grant to the NASA Lewis Research Center, scientists at the Case Western Reserve University have been examining the use of modern computing techniques that may be able to investigate and find the behavior of complete systems that have a large number of particles by tracking each particle individually. This is the study of molecular dynamics. In contrast to Monte Carlo techniques, which incorporate uncertainty from the outset, molecular dynamics calculations are fully deterministic. Although it is still impossible to track, even on high-speed computers, each particle in a system of a trillion trillion particles, it has been found that such systems can be well simulated by calculating the trajectories of a few thousand particles. Modern computers and efficient computing strategies have been used to calculate the behavior of a few physical systems and are now being employed to study important problems such as supersonic flows in the laboratory and in space. In particular, an animated video (available in mpeg format--4.4 MB) was produced by Dr. M.J. Woo, now a National Research Council fellow at Lewis, and the G-VIS laboratory at Lewis. This video shows the behavior of supersonic shocks produced by pistons in enclosed cylinders by following exactly the behavior of thousands of particles. The major assumptions made were that the particles involved were hard spheres and that all collisions with the walls and with other particles were fully elastic. The animated video was voted one of two winning videos in a competition held at the meeting of the American Physical Society's Division of Fluid Dynamics, held in Atlanta, Georgia, in November 1994. Of great interest was the result that in every shock there were a few high-speed precursor particles racing ahead of the shock, carrying information about its impending arrival. Most recently, Dr. Woo has been applying molecular dynamics techniques to the problem of determining the drag produced by the space station truss structure as it flies through the thin residual atmosphere of low-Earth orbit. This problem is made difficult by the complex structure of the truss and by the extreme supersonic nature of the flow. A fully filled section of the truss has already been examined, and drag predictions have been made. Molecular dynamics techniques promise to make realistic drag calculations possible even for very complex partially filled truss segments flying at arbitrary angles.

Source record↗

DOE OSTI2026

Quantum scattering of HC 5 N and para -H 2 on a new potential energy surface

In the interstellar medium (ISM), non-local thermodynamic equilibrium situations are common due to low density, and one needs to consider the effect of molecular collisions in order to interpret the observations. Among the species detected in the ISM, cyanopolyynes, with the general molecular formula HC 2n+1 N (n = 1, 2, …), are characterized by large dipole moments and small rotational constants and constitute an indispensable class of candidates for the sensitive tracers of local density and temperature. We present a study of the collisional (de-) excitation of HC 5 N by para -H 2 (p-H 2 ) in its ground rotational state, namely HC 5 N ( j 1 ) + H 2 ( j 2 = 0) → HC 5 N (j$_1^′$) + H2 (j$_2^′$ = 0), where j 1 (or j$_1^′$) and j 2 (or j$_2^′$) denote the initial (or final) rotational quantum numbers of HC 5 N and H 2 , respectively. We performed the quantum scattering calculations at low collision energy using a new four-dimensional ab initio potential energy surface. In the regime where p-H 2 remains in its rotational ground state, converged cross sections did not require including excited rotational states of p-H 2 in the rotational basis. State-to-state cross sections were computed by means of the quantum-mechanical close-coupling (CC) method and the coupled states (CS) approximation, and rate coefficients for the first 61 levels of HC 5 N were computed for the first time up to 20 K with the CC approach and up to 50 K with the CS method. CC and CS results were found to agree well at temperatures up to 20 K. Finally, these data should allow a more accurate derivation of the HC 5 N abundance in molecular clouds.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2020

Observation of a new baryon state in the $Λ^0_bπ^+π^-$ mass spectrum

A new baryon state is observed in the $Λ^0_bπ^+π^-$ mass spectrum with high significance using a data sample of pp collisions, collected with the LHCb detector at centre-of-mass energies $\sqrt{s}$ = 7, 8 and 13 TeV, corresponding to an integrated luminosity of 9 fb -1 . The mass and natural width of the new state are measured to be m = 6072.3 ± 2.9 ± 0.6 ± 0.2 MeV , Γ = 72 ± 11 ± 2 MeV , where the first uncertainty is statistical and the second systematic. The third uncertainty for the mass is due to imprecise knowledge of the $Λ^0_b$ baryon mass. The new state is consistent with the first radial excitation of the $Λ^0_b$ baryon, the Λ b (2S) 0 resonance. Updated measurements of the masses and the upper limits on the natural widths of the previously observed Λ b (5912) 0 and Λ b (5920) 0 states are also reported.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2022

Manifestation of postcollision interaction in Krypton LMN Auger spectra following K-shell photoionization

In this work, we report on an experimental and theoretical study of post-collision interaction (PCI) effects on L 2 -M 4,5 N 2,3 Auger electrons measured above the Kr K-edge in which L 2 vacancies are primarily generated by KL 2 x-ray emission. Such cascade processes, in which a deep inner-shell vacancy decays first by x-ray emission followed by Auger electron emission, is a strong decay mode in heavy atoms. The L 2 -M 4,5 N 2,3 Auger electron peak is observed to become increasingly asymmetric with a shifting peak maximum as the absorbed x-ray energy approaches the K-shell ionization threshold. This is attributed to PCI energy exchanges of the Auger electron with the 1s photoelectron. To model the PCI effects, we have applied a semiclassical approach modified to account for the combined lifetimes of the K and L 2 hole states. In addition, our analysis treats several closely spaced Auger transitions with final ionic states having different terms and angular momenta.

74 ATOMIC AND MOLECULAR PHYSICS↗

DOE OSTI2022

Far-from-equilibrium slow modes and momentum anisotropy in expanding plasma

The momentum distribution of particle production in heavy-ion collisions encodes information about thermalization processes in the early-stage quark-gluon plasma. We use kinetic theory to study the far-from-equilibrium evolution of an expanding plasma with an anisotropic momentumspace distribution. We identify slow and fast degrees of freedom in the far-from-equilibrium plasma from the evolution of moments of this distribution. At late times, the slow modes correspond to hydrodynamic degrees of freedom and are naturally gapped from the fast modes by the inverse of the relaxation time, $τ$$^{–1}_{R}$. At early times, however, there are an infinite number of slow modes with a gap inversely proportional to time, τ –1 . From the evolution of the slow modes we generalize the paradigm of the far-from-equilibrium attractor to vector and tensor components of the energy momentum tensor, and even to higher moments of the distribution function that are not part of the hydrodynamic evolution. We predict that initial-state momentum anisotropy decays slowly in the far-from-equilibrium phase and may persist until the relaxation time.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2021

Measurement of the branching fraction of the ${{B} ^0} {\rightarrow }{{D} ^+_{s}} {{\pi } ^-} $ decay

A branching fraction measurement of the ${{B} ^0} {\rightarrow }{{D} ^+_{s}} {{\pi } ^-} $ decay is presented using proton–proton collision data collected with the LHCb experiment, corresponding to an integrated luminosity of $5.0\,\text {fb} ^{-1} $ . The branching fraction is found to be ${\mathcal {B}} ({{B} ^0} {\rightarrow }{{D} ^+_{s}} {{\pi } ^-} ) =(19.4 \pm $ $1.8\pm 1.3 \pm 1.2)\times 10^{-6}$ , where the first uncertainty is statistical, the second systematic and the third is due to the uncertainty on the ${{B} ^0} {\rightarrow }{{D} ^-} {{\pi } ^+} $ , ${{D} ^+_{s}} {\rightarrow }{{K} ^+} {{K} ^-} {{\pi } ^+} $ and ${{D} ^-} {\rightarrow }{{K} ^+} {{\pi } ^-} {{\pi } ^-} $ branching fractions. This is the most precise single measurement of this quantity to date. As this decay proceeds through a single amplitude involving a $b{\rightarrow }u$ charged-current transition, the result provides information on non-factorisable strong interaction effects and the magnitude of the Cabibbo–Kobayashi–Maskawa matrix element $V_{ub}$ . Additionally, the collision energy dependence of the hadronisation-fraction ratio $f_s/f_d$ is measured through ${{\overline{B}} {}^0_{s}} {\rightarrow }{{D} ^+_{s}} {{\pi } ^-} $ and ${{B} ^0} {\rightarrow }{{D} ^-} {{\pi } ^+} $ decays.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2022

Sequential Bond Dissociation Energies of Th + (CO) x , x = 3–6: Guided Ion Beam Collision-Induced Dissociation and Quantum Computational Studies

Collision-induced dissociation (CID) of [Th,xC,xO] + , x = 3–6, with Xe is performed using a guided ion beam tandem mass spectrometer (GIBMS). Products are formed exclusively by the loss of CO ligands. Analyses of the kinetic energy-dependent CID product cross sections yield bond dissociation energies (BDEs) of (CO) x–1 Th + –CO at 0 K as 1.09 ± 0.05, 0.82 ± 0.07, 0.63 ± 0.05, and 0.70 ± 0.05 eV, respectively. Different structures of [Th,xC,xO] + were explored using various electronic structure methods, and BDEs for CO ligand loss from precursor [Th,xC,xO] + complexes were computed. Both experimental and theoretical results corroborate that the structures of [Th,xC,xO] + , x = 3–6, formed experimentally are homoleptic thorium cation carbonyl complexes, Th + (CO) x . The nonmonotonic trend in experimental BDEs is reproduced theoretically, although ambiguities in the spin states of the x = 4–6 complexes (doublet or quartet) remain. BDEs calculated at the coupled cluster with single, double, and perturbative triple excitations (CCSD(T))/cc-pVXZ//B3LYP/cc-PVXZ (X = T and Q) level and a complete basis set (CBS) extrapolation agree reasonably well with the experimental values for all complexes. Thorium oxide ketenylidene carbonyl cations, OTh + CCO(CO) y , y = 1–4, were calculated to be the most stable structures of [Th,xC,xO] + , x = 3–6, respectively; however, these are not observed in our experiment. Potential energy profiles (PEPs) having either quartet or doublet spin calculated at the B3LYP/cc-pVQZ level suggest that the failure to observe OTh + CCO(CO) y , y = 1–4, is the result of a barrier corresponding to the C–C bond formation, making the formation of OTh + CCO(CO) y inaccessible kinetically under the present experimental conditions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗