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Previous ab initio studies have consistently predicted phosphine oxide (H[sub 3]PO) to be less stable than its nearly isoenergetic cis- and trans-phosphinous acid isomers (H[sub 2]POH). However, complete basis set extrapolations employing the coupled-cluster series show that phosphine oxide is actually ca. 1.0 kcal/mol more stable than its acid forms in the gas phase. Incorporation of tight d functions via Dunning’s core-valence (cc-pCVXZ) or newly constructed “plus d” [cc-pV(X+d)Z] basis sets is essential for rapid convergence of core polarization effects which are evident even at the SCF level. The precision to which the phosphorus hybridization is described in the three- and four-coordinate environments ultimately determines the predicted gas-phase relative energy orderings. Focal-point analyses demonstrate that this system represents a disturbing case where use of a conventional valence quadruple-ζ quality basis set (cc-pVQZ)—even at the CCSD(T) level—fails to provide the correct relative energy ordering for simple closed-shell species which do not exhibit appreciable multireference character. Thus, we underscore the importance of using phosphorus basis sets which have the flexibility to describe core polarization adequately. In addition, Monte Carlo (MC) free-energy perturbation simulations in solution clearly demonstrate that the small energy gap significantly increases in favor of the oxide (10.0 kcal/mol) upon solvation due to stronger hydrogen bonding with the highly polar P[sup δ+]→O[sup δ-] bond. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The cultivation-independent analyses based on genetic profiling of partial bacterial 16S rRNA genes are applied to characterize the diversity of metabolically active bacteria in the larval gut of Manduca sexta bred on tobacco leaves under greenhouse conditions. The findings from the study provide a powerful approach to explore the origin, diversity, and metabolic activity of the bacterial community associated with insect larvae and interactions between insects and microorganisms.

The structures of a ditopic, macrobicyclic receptor, complexed with KAcO, LiNO3, NaNO3, KNO3 and NaNO2 are characterized in solution by NMR spectroscopy and in the solid state by X-ray crystallography. The sodium and potassium salts are bound to the receptor as contact ion-pairs, with the metal cation located in the receptor's crown ether ring and the trigonal oxyanion hydrogen bonded to the receptor NH residues.

The B3LYP density functional method is used to determine the optimized geometries harmonic vibrational frequencies and anharmonic vibrational frequencies of HPO2 and the trans- and cis-isomers of HOPO. The isotropic hyperfine splitting (ifs) constants and the vibrationally averaged hfs are determined for the radical anions of each species.

Studies the electron affinities of the oxides of aluminum, silicon, phosphorus, sulfur and chlorine using different density functional or hybrid Hartree-Fock/density functional methods. Zero-point vibrational energy corrected electron affinities; Equilibrium geometries and vibrational frequencies.

Equilibrium structures and harmonic vibrational frequencies were computed for adamantane (Ad), the 1- and 2-adamantyl radicals, cations and anions. Four different density functional and hybrid Hartree-Fock/density functional methods are used to predict ionization potentials and electron affinities of Ad, 1-Ad., and 2-Ad.

The adiabatic electron affinity (EA) of sulfur hexafluoride (SF6) was determined using six different density functional or hybrid Hartree–Fock/density functional methods, including the recently developed KMLYP functional. With the extensively calibrated DZP++ basis set, the KMLYP functional predicts an EA for SF6 of 1.48 eV. This value is in better agreement with experiment (1.07 ± 0.01 eV) than the best previously established DFT method (BHLYP, 1.69 eV) for related systems. The other four functional give electron affinities of 2.66 (B3LYP), 2.83 (B3P86), 3.22 (BLYP), and 3.00 eV (BP86). However, the difference from the experimental value is still about twice a large as DFT is usually able to obtain. [Copyright &y& Elsevier]

The X˜2A1 and a˜4A2 electronic states of the methylene cation, CH2+, were investigated using the coupled cluster method with singles, doubles, and perturbatively applied triples [CCSD(T)] with Dunning's correlation consistent polarized valence basis set series (cc-pVXZ, where X=T, Q, and 5), core-valence basis sets (cc-pCVXZ, where X=T and Q), and augmented basis sets (aug-cc-pVXZ, where X=Q and 5). Explicit computation of the full set of triples (CCSDT) was also performed with the cc-pVTZ basis set. The most reliable equilibrium structures of re=1.094 A˚ and θe=140.4° (X˜2A1) and re=1.190 A˚ and θe=77.1° (a˜4A2) were obtained at the CCSD(T)/aug-cc-pV5Z level. The X˜2A1–a˜4A2 classical energy separation is predicted to be 86.9 kcal/mol (30 400 cm−1, 3.77 eV) at the CCSD(T)/cc-pCVQZ level of theory, and the zero-point vibrational energy corrected value is 84.5 kcal/mol (29 500 cm−1, 3.66 eV). [Copyright &y& Elsevier]

High-level coupled-cluster theory with large basis sets was used to determine the optimized geometries and harmonic vibrational frequencies for the ground and low-lying excited electronic states of the CH[sub 2]N and CH[sub 2]P radicals. Additionally, isotropic hyperfine splitting constants were determined for the C[sub 2v] CH[sub 2]X, trans-HCXH and cis-HCXH (where X=N and P) isomers as a gauge of the delocalization of the unpaired electron. The geometrical parameters of X˜ [sup 2]B[sub 2] CH[sub 2]X, the trans-HCXH and cis-HCXH conformers, and the first three excited states are reported at the coupled-cluster level with single, double, and perturbatively applied triple excitations [CCSD(T)] using Dunning's correlation consistent polarized valence quadruple-ζ basis set (cc-pVQZ). The C[sub 2v] structures on the ground state surface are predicted to lie 9.3 and 13.5 kcal/mol lower than the trans- and cis-isomers, respectively, for CH[sub 2]N and 28.1 and 30.0 kcal/mol, respectively, for CH[sub 2]P. There are many other important properties of CH[sub 2]N and CH[sub 2]P which are not known from experiment. The geometrical parameters of the CH[sub 2]N ground state [r(C-N)=1.2462 Å, r(C-H)=1.0921 Å, and θ(HCH)=119.4°] and the CH[sub 2]P ground state [r(C-P)=1.6583 Å, r(C-H)=1.0842 Å, and θ(HCH)=118.9°] agree well with the C-N and C-P bond distances of the r[sub 0] structures derived from microwave data, although notable differences were observed in the C-H bond distance and HCH bond angle. This research resolves an earlier discrepancy between theory and experiment for the ground state C-P distance in CH[sub 2]P. The Fermi contact terms for [sup 1]H, [sup 13]C, [sup 14]N, and [sup 31]P were determined at CCSD(T) level of theory with the cc-pVTZ and cc-pVQZ basis sets and are in reasonable agreement with the experimental values with a maximum deviation of 26 MHz for CH[sub 2]N and 11 MHz for CH[sub 2]P. The ... [ABSTRACT FROM AUTHOR]

The potential energy surface and dipole moment surfaces of the a˜4A2 electronic state of CH2+ are calculated ab initio using an augmented correlation-consistent polarized valence quadruple-ζ (aug-cc-pVQZ) basis set, with the incorporation of dynamical correlation using the coupled cluster method with single and double excitations and perturbatively connected triple excitations [CCSD(T)]. We use these surfaces in the MORBID program system to calculate rotation and rotation–vibration term values for a˜-state CH2+, CD+2, and CHD+ and to simulate the rotation and rotation–vibration absorption spectrum of CH2+ in the a˜4A2 electronic state. Our work is motivated by studies of CH2+ that use the Coulomb explosion imaging technique and by the goal of predicting spectra that may be obtained from discharge sources. Although the a˜ state is the lowest-lying excited state above the X˜/A˜ ground state pair, it turns out to be relatively high-lying, and we determine that Te(a˜)=30447.5 cm−1. The equilibrium bond angle for a˜-state CH2+ is only 77.1°; as a result the asymmetric top κ value is close to 0, and the molecule is equally far from the oblate and prolate symmetric top limits in this electronic state. [Copyright &y& Elsevier]

Chlorella and Stichococcus are morphologically simple airborne microalgae, omnipresent in terrestrial and aquatic habitats. The minute cell size and resistance against environmental stress facilitate their long-distance dispersal. However, the actual distribution of Chlorella- and Stichococcus-like species has so far been inferred only from ambiguous morphology-based evidence. Here we contribute a phylogenetic analysis of an expanded SSU and ITS2 rDNA sequence dataset representing Chlorella- and Stichococcus-like species from terrestrial habitats of polar, temperate and tropical regions. We aim to uncover biogeographical patterns at low taxonomic levels. We found that psychrotolerant strains of Chlorella and Stichococcus are closely related with strains originating from the temperate zone. Species closely related to Chlorella vulgaris and Muriella terrestris, and recovered from extreme terrestrial environments of polar regions and hot deserts, are particularly widespread. Stichococcus strains from the temperate zone, with their closest relatives in the tropics, differ from strains with the closest relatives being from the polar regions. Our data suggest that terrestrial Chlorella and Stichococcus might be capable of intercontinental dispersal; however, their actual distributions exhibit biogeographical patterns., (© FEMS 2016. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)