Small Internuclear Separations Research Articles

Optical imaging with a high-resolution microendoscope to identify sinonasal pathology

ObjectivesHigh-resolution microendoscopy (HRME) is an optical imaging modality that allows real time imaging of epithelial tissue and structural changes within. We hypothesize that HRME, using proflavine, a contrast agent that preferentially stains cell nuclei and allows detection of cellular morphologic changes, can distinguish sinonasal pathology from uninvolved mucosa, potentially enabling real-time surgical margin differentiation. Study designEx vivo imaging of histopathologically confirmed samples of sinonasal pathology and uninvolved, normal sinus epithelium. SettingSingle tertiary-level institution. Subjects and methodsFive inverted papillomas, one oncocytic papilloma, two uninvolved sinus epithelia specimens, and three inflammatory polyps were imaged ex vivo with HRME after surface staining with proflavine. Following imaging, the specimens were submitted for hematoxylin and eosin staining to allow histopathological correlation. ResultsResults show that sinonasal pathology and normal sinus epithelia have distinct HRME imaging characteristics. Schneiderian papilloma specimens show increased nuclear-to-cytoplasmic ratio, nuclear crowding, and small internuclear separation, whereas normal sinus epithelia specimens show small, bright nuclei with dark cytoplasm and relatively large internuclear separation. Inflammatory polyps, however, have varying imaging characteristics, that resemble both Schneiderian papilloma and normal sinus epithelia. ConclusionsThis study demonstrates the feasibility of HRME imaging to discriminate sinonasal pathology from normal sinus epithelia. While the system performed well in the absence of inflammation, discrimination of inflamed tissue was inconsistent, creating a significant limitation for this application. Novel imaging systems such as HRME with alternative contrast agents may assist with real-time surgical margin differentiation, enabling complete surgical resection of inverted papilloma and reducing recurrence rates.

Rydberg blockade in a hot atomic beam

The dipole blockade of very-high-$n, n\ensuremath{\sim}300$, strontium $5snf{\phantom{\rule{0.16em}{0ex}}}^{1}{F}_{3}$ Rydberg atoms in a hot atomic beam is studied. For such high $n$, the blockade radius can exceed the linear dimensions of the excitation volume. Rydberg atoms formed inside the excitation volume can, upon leaving the region, continue to suppress excitation until they have moved farther away than the blockade radius. Moreover, the high density of states originating from the many magnetic sublevels associated with the $F$ states results in a small but finite probability of excitation of $L=3\phantom{\rule{0.28em}{0ex}}n{\phantom{\rule{0.16em}{0ex}}}^{1}{F}_{3}$ atom pairs at small internuclear separations below the blockade radius. We demonstrate that these effects can be distinguished from one another by the distinct features they imprint on the Mandel $Q$ parameter as a function of the duration of the exciting laser.

Xe2 gerade Rydberg states observed in the afterglow of a microplasma by laser spectroscopy of a(3)Σ(+)(u)(1(u), O(-)(u)) absorption in the green (545-555 nm) and near-infrared (675-800 nm).

Bound←bound transitions of the Xe dimer at small internuclear separation (R < 4.0 Å) have been observed in the 545-555 nm and 675-800 nm spectral regions by laser spectroscopy in the afterglow of a pulsed Xe microplasma with a volume of ∼160 nl. Transient suppression of Xe2 A(1)Σ(+)(u)(O(+)(u)) --> X(1)Σ(+)(g)(O(+)(g)) emission in the vacuum ultraviolet (∼172 nm), induced by laser excitation of Ω(g) ← a(3)Σ(+)(u)(1(u), O(-)(u)) [Rydberg←Rydberg] transitions of the molecule, has confirmed the existence of structure between 720 and 770 nm (reported by Killeen and Eden [J. Chem. Phys. 84, 6048 (1986)]) but also reveals red-degraded vibrational bands extending to wavelengths beyond 800 nm. Spectral simulations based on calculations of Franck-Condon factors for assumed Ω(g) ← a(3)Σ(+)(u) transitions involving Ω = 0(±),1 gerade Rydberg states suggest that the upper level primarily responsible for the observed spectrum is an Ω = 1 state correlated, in the separated atom limit, with Xe(5p(6) (1)S0) + Xe(5p(5) 6p) and built on a predominantly A(2)Π3/2g molecular ion core. Specifically, the spectroscopic constants for the upper state of the 1(g) ← 1(u), O(±)(u) absorptive transitions are determined to be Te = 13,000 ± 150 cm(-1), ω'(e) = 120 ± 10 cm(-1), ω'(e)x'(e) = 1.1 ± 0.4 cm(-1), De = 3300 ± 300 cm(-1), and ΔR(e) = R'(e) = R''(e) = 0.3 ± 0.1 Å which are in general agreement with the theoretical predictions of the pseudopotential hole-particle formalism, developed by Jonin and Spiegelmann [J. Chem. Phys. 117, 3059 (2002)], for both the (5)1g and (3)O(+)(g) states of Xe2. These spectra exhibit the most extensive vibrational development, and provide evidence for the first molecular core-switching transition, observed to date for any of the rare gas dimers at small R (<4 Ǻ). Experiments in the green (545-555 nm) also provide improved absorption spectra, relative to data reported in 1986 and 1999, associated with Xe2 Rydberg states derived from the Xe(7p) orbital.

Mechanisms underlying strong-field double ionization of argon dimers

We investigate double ionization of argon dimers in high-intensity ultrashort Ti:sapphire laser pulses. We are able to identify several strong-field excitation pathways of the dimer that terminate in atomic ion pairs from a Coulomb explosion. The explosion starts from two-site double-ionized dimers and from one-site double-ionized ones after radiative charge transfer at small internuclear separation. One-site double ionization is accomplished by laser-induced charge transfer in the high-intensity laser pulse following two-site double ionization. The highest energy ion pairs we observed can be attributed to ``frustrated triple ionization'' of the argon dimer.

On some aspects of changing the sign of the dipole moment functions of diatomic molecules

Ab initio calculations of asymptotic dipole moment functions of some diatomic molecules at R → 0 have been carried out. It was achieved that in a range of small internuclear separations, the dipole moment functions of the molecules CO, NO, BF and BeNe for ground electronic states have an additional change of the sign.

General regularities in the behavior of dipole moment functions of diatomic molecules at small internuclear separations

Based on the united atom model and the LS-coupling approximation, dipole moment functions were calculated for some diatomic molecules at small internuclear separations R. Families of molecules belonging to united atoms Li(2S), Na(2S), B(1P), Al(1P), and O(1D) were considered. It was shown that dipole moment functions at R → 0 satisfy the asymptotic dependence μ(R) =AR3. The regularities in the behavior of the functions μ(R) were determined depending on the electronic state and nuclei charges of molecules. The obtained systematic features are in good agreement with the results calculated for molecules whose united atoms are in groups II, IV, V, VII, and VIII of the Periodic Table.

Regularities in the behavior of dipole moment functions of diatomic molecules at very small internuclear separations

A theoretical approach to calculating the dipole moment function of a diatomic molecule at very small internuclear separations has been suggested. The approach is based on the united-atom model and the LS-coupling approximation. Regularities in the behavior of the dipole moments as functions of the internuclear separation, electronic state, and nuclear charge of the molecule have been found. Within the approach, the dipole moment functions of some diatomic molecules, whose united atoms are in groups II, IV, V, VII, and VIII of periods 1–4 of the periodic table, were calculated.

Performance of the Spin-Flip and Multireference Methods for Bond Breaking in Hydrocarbons: A Benchmark Study

Benchmark results for spin-flip (SF) coupled-cluster and multireference (MR) methods for bond-breaking in hydrocarbons are presented. The nonparallelity errors (NPEs), which are defined as an absolute value of the difference between the maximum and minimum values of the errors in the potential energy along bond-breaking curves, are analyzed for (i) the entire range of nuclear distortions from equilibrium to the dissociation limit and (ii) in the intermediate range (2.5-4.5 A), which is the most relevant for kinetics modeling. For methane, the spin-flip and MR results are compared against full configuration interaction (FCI). For the entire potential energy curves, the NPEs for the SF model with single and double substitutions (SF-CCSD) are slightly less than 3 kcal/mol. Inclusion of triple excitations reduces the NPEs to 0.32 kcal/mol. The corresponding NPEs for the MR-CI are less than 1 kcal/mol, while those of multireference perturbation theory are slightly larger (1.2 kcal/mol). The NPEs in the intermediate range are smaller for all of the methods. The largest errors of 0.35 kcal/mol are observed, surprisingly, for a spin-flip approach that includes triple excitations, while MR-CI, CASPT2, and SF-CCSD curves are very close to each other and are within 0.1-0.2 kcal/mol of FCI. For a larger basis set, the difference between MR-CI and CASPT2 is about 0.2 kcal/mol, while SF-CCSD is within 0.4 kcal/mol of MR-CI. For the C-C bond breaking in ethane, the results of the SF-CCSD are within 1 kcal/mol of MR-CI for the entire curve and within 0.4 kcal/mol in the intermediate region. The corresponding NPEs for CASPT2 are 1.8 and 0.4 kcal/mol, respectively. Including the effect of triples by energy-additivity schemes is found to be insignificant for the intermediate region. For the entire range of nuclear separations, sufficiently large basis sets are required to avoid artifacts at small internuclear separations.

A dipole-moment function of MeH molecules (Me = Li, Na, K))

The dipole-moment functions of the ground states of LiH, NaH, and KH molecules at small internuclear separations are calculated. Based on these calculations, the dipole-moment functions of molecules under consideration are derived for a wide range of internuclear separations. To this end, use was made of the cubic spline interpolation of the dipole-moment functions calculated in this work and those known ab initio.

Analysis of the bonding in alkali-cation/Rg complexes (Rg = He–Xe) using a simple model potential

We have applied the model-potential analysis of Breckenridge and co-workers to the Alk +/Rg systems, where Alk is an alkali atom and Rg is a rare-gas atom. Three spectroscopic constants, R e, D e and ω e, are employed to obtain the potential, with fitted parameters being the A and b repulsive Born–Mayer potential parameters, and the effective charge on the metal center, Z. From the analysis, it is concluded that all of these systems can be described in physical terms, with the calculated charge on the metal center being very close to 1.00. Interestingly the effective charge on the metal atom from such model-potential calculations is consistently very slightly greater than 1.00. We discuss and investigate several possible sources for this small anomaly, including a minor breakdown of the model at small internuclear separations, where the “lengths” of the induced multipoles become significant compared to the internuclear separation R. Despite this small breakdown, overall the model is remarkably successful in reproducing high-level ab initio curves for the titular complexes over wide ranges of internuclear distances.

Theoretical investigation into dipole-moment functions of HF, HCl, and HBr molecules at small internuclear separations

Ab initio calculations of the dipole moment functions are performed within the united atom approximation in the first-order perturbation theory for the ground electronic states of HF, HCl and HBr molecules in the range of small internuclear separations. The calculation results are used for correction of the semi-empirical dipole-moment functions of these molecules obtained earlier.

High-order harmonic generation in laser-irradiated homonuclear diatomics: The velocity gauge version of the molecular strong-field approximation

The generation of high harmonics in laser-irradiated light homonuclear diatomics (H2+, N2 and O2) compared to that in atomic counterparts (of nearly identical binding energy) is studied within the velocity gauge version of conventional strong-field approximation. The applied strong-field approach (we alternatively developed earlier to incorporate rescattering effects beyond the conventional saddle-point approximation) is currently extended to molecular case by means of supplement the standard linear combination of atomic orbitals} and molecular orbitals method. The associated model proved to adequately reproduce a general shape and detailed structure of molecular harmonic spectra, which demonstrate a number of remarkable distinctive differences from respective atomic spectra calculated under the same laser pulses. The revealed differences are found to be strongly dependent on internuclear separation and also very sensitive to the orbital and bonding symmetry of contributing molecular valence shell. In particular, the model correctly predicts the behavior of high-frequency plateau (both for its extent and even details of structure) in molecular harmonic spectra at small (nearly equilibrium) and large internuclear separations. In addition, for some group of harmonics, the harmonic emission rates were ascertained to dominate by contribution from inner molecular shells of higher binding energy and different orbital symmetry compared to the outermost molecular orbital normally predominantly contributing.

Gerade Rydberg states of Xe 2 probed by laser spectroscopy in the afterglow of a Xe microplasma: [formula omitted] transitions in the near-infrared (675–800 nm)

Gerade Rydberg states of Xe 2 lying 12 500–14 800 cm −1 above the a 3 Σ u + ( 1 u , O u - ) metastable levels of the dimer have been observed by laser spectroscopy in the afterglow of a Xe microplasma with a volume of ∼160 nL. Photoexcitation of Ω g ← a 3 Σ u + ( 1 u , O u - ) (Rydberg ← Rydberg) state transitions at small internuclear separations ( R ≃ R e ( Xe 2 + ) ) while monitoring the suppression of Xe 2 ( O u + → O g + ) spontaneous emission in the ultraviolet confirms the presence of an extensive series of red-degraded vibrational bands in the 675–800 nm region that are tentatively identified with an Ω = 1 upper state with a molecular ion core having predominantly B 2Π 3/2g character. Spectral simulations yield the following constants for the 1 g state: R e ′ = 3.49 ± 0.1 Å , T e = 12 980 ± 70 cm −1, ω e ′ = 122 ± 3 cm −1, ω e ′ x e ′ = 0.9 ± 0.2 cm −1, and D e ′ = 2250 ± 70 cm −1.

The semiempirical dipole moment functions of the molecules HX (X = F, Cl, Br, I, O), CO and NO

A semiempirical method is suggested to construct the dipole moment function for a diatomic molecule in the form of a piecewise-continuous function that exhibits physically correct behaviour at small and large internuclear separations and agrees with the dipole moment function near the equilibrium position of molecule nuclei. The dipole moment functions are calculated for the ground electron states of the molecules HF, HCl, HBr, HI, OH, NO and CO for all ranges of internuclear separations.

Observing negligible collision trap losses: The case of alkaline-earth metals

We show that when cold collisions account for just a few percent of the total loss in magneto-optical traps, as for alkaline-earth metals, their contribution can be obtained by comparing the load and decay quasiexponential curves. We exemplify it by measuring the collision rate coefficient \ensuremath{\beta} for calcium atoms at small trap laser detuning, which confirms the role of the long-lived ${}^{1}{\ensuremath{\Pi}}_{g}$ state at small internuclear separation. Systematic and simpler measurements of \ensuremath{\beta} for alkaline-earth metals are important for cold collision theory, since these elements have nondegenerate ground state and no hyperfine structure. Our method has general applicability and should considerably reduce the experimental challenges associated with these important measurements.

Topology of electron correlation in the b [formula omitted] state of the H 2 molecule

Except for the united atom limit, the correlation cage of the b 3 Σ + u state of H 2 is isomorphic to that of the ground state. However, encompassing a genuine cage point rather than a cusp, it is associated primarily with the Fermi hole. Although the spatial extent of the cage evolves continuously with the internuclear separation R, it varies sharply around R=2.0 a.u., indicating a change in the dominant electronic configuration. Unlike in the case of the EF 1 Σ + g state of H 2, the electronic configurations that dominate at small and large internuclear separations share a single topology of the intracule density.

Origin of the structures in the excitation cross sections in ion-atom collisions

It is demonstrated that the structures in the low-energy cross sections for excitation to certain levels of atoms by ions originate from a shift from direct excitation at high and intermediate energies to pronounced two-center molecular mechanisms at lower energies. The molecular mechanisms dominate at small internuclear separations, whereas the direct mechanism is driven by the familiar dipole long-range coupling. The demonstration is based on maps of the excitation probabilities over the collision velocity and impact parameter, which display two typical regions. System specific details determine the separation between the two regions and give rise to a plateau, an oscillation or a hidden shoulder in the excitation cross sections. Maps of classical-trajectory Monte Carlo method results show similar qualitative features, but the details of these maps differ considerably from those of the quantal calculations.

Bihalide ion combination reactions in solution: electronic structure and solvation aspects

The Kim—Hynes theory for electronic structure for reaction systems in solution is applied to the reaction class of the title, focusing on the I - +I → I 2 - reaction in acetonitrile solvent from a valence bond perspective. The transition between a delocalized electronic structure at small internuclear separations r to localized structures at large r is described in terms of a two-dimensional nonequilibrium free energy surface; the second coordinate is a solvent coordinate gauging the state of the solvent orientational polarization. The reaction path on this surface is described, and is contrasted with an equilibrium solvation perspective. An important focus is the polarization force, defined as the force on the diatomic ion coordinate r due to the solvent, which arises from the charge shifting, or electronic structure change, in the solute system along the reaction coordinate. It is argued that this force should play a significant role in the vibrational relaxation of the I 2 - ion.

The electronic structure of the dipolar atomic state in a centrosymmetric environment

A point polarizable atom model calculation predicts that a linear symmetric triatomic system will undergo a transition to a dipolar state at small internuclear separations. For the BeLiBe system, this is confirmed by ab initio quantum chemistry computations. The point polarizable atom calculation is readily generalizable to any centrosymmetric system which is similarly predicted to undergo a transition to a dipolar state at sufficiently small interatomic spacings. The need to apply external probing fields to derive information about any system shows that symmetry based quantum mechanical arguments against dipolar states in centrosymmetric systems are not necessarily valid. These quantum arguments become less significant as the number of atoms in the system increases and do not apply to an infinite system; this is a manifestation of the correspondence principle.

Electron detachment in low-energy collisions of halogen anions with atomic hydrogen.

Total electron-detachment cross sections ${\mathrm{\ensuremath{\sigma}}}_{\mathit{e}}$ for collisions of ${\mathrm{F}}^{\mathrm{\ensuremath{-}}}$, ${\mathrm{Cl}}^{\mathrm{\ensuremath{-}}}$, ${\mathrm{Br}}^{\mathrm{\ensuremath{-}}}$, and ${\mathrm{I}}^{\mathrm{\ensuremath{-}}}$ with atomic hydrogen have been measured for relative collision energies E ranging from 0.1 to 20 eV. For ${\mathrm{F}}^{\mathrm{\ensuremath{-}}}$, ${\mathrm{Cl}}^{\mathrm{\ensuremath{-}}}$, and ${\mathrm{Br}}^{\mathrm{\ensuremath{-}}}$, ${\mathrm{\ensuremath{\sigma}}}_{\mathit{e}}$ is found to decrease with increasing E and is fairly well described by a simple orbiting model in which an effective polarizability is used to describe the interaction of the anion with atomic hydrogen at small internuclear separations. For the system ${\mathrm{I}}^{\mathrm{\ensuremath{-}}}$+H, ${\mathrm{\ensuremath{\sigma}}}_{\mathit{e}}$ increases with increasing collision energy. The measured ${\mathrm{\ensuremath{\sigma}}}_{\mathit{e}}$ for ${\mathrm{Cl}}^{\mathrm{\ensuremath{-}}}$+H is also found to agree well with calculations based on an effective-range approximation. Charge-transfer cross sections have been measured for ${\mathrm{F}}^{\mathrm{\ensuremath{-}}}$, ${\mathrm{Cl}}^{\mathrm{\ensuremath{-}}}$, and ${\mathrm{I}}^{\mathrm{\ensuremath{-}}}$+H and are found to be small.