Classification of drying segregation states by a generalized diffusion model.

During drying of binary colloidal mixtures, one colloidal particle component can segregate to the top surface. We investigate conditions where the segregation occurs through the analysis of a linearized diffusion model with Fick's law generalized for binary colloidal mixtures. The present model is the simplest representation that includes cross-diffusion between different particle components to describe the segregation. Using the analytical solutions of this model, we classify states in terms of which the particle component segregates for the following variables: the mixture ratio of particle components, diffusion coefficients, and drying rates. The obtained state diagrams suggest how to control the segregation by designing material and operation conditions.

Mesoscale modeling of colloidal suspensions with adsorbing solutes.

We construct a mesoscale model of colloidal suspensions that contain solutes reversibly adsorbing onto the colloidal particle surfaces. The present model describes the coupled dynamics of the colloidal particles, the host fluid, and the solutes through the Newton-Euler equations of motion, the hydrodynamic equations, and the advection-diffusion equation, respectively. The solute adsorption is modeled through a square-well potential, which represents a short-range attractive interaction between a particle and a solute molecule. The present model is formulated to be solved through direct numerical simulations. Some numerical results are presented to validate the simulations. The present model enables investigations of solute adsorption effects in the presence of a fluid flow and an inhomogeneous solute concentration distribution.

Aggregates of silicon quantum dots as a drug carrier: selective intracellular drug release based on pH-responsive aggregation/dispersion.

Using amine-modified silicon quantum dots (Si-QDs) with visible photoluminescence as a building block, drug-loaded Si-QD aggregates were assembled. The aggregates were designed to break down in response to the endosomal pH decrease, which enabled the selective intracellular release of the loaded drugs.

BeCH2: the simplest metal carbene. High levels of theory.

The simplest metal carbene, BeCH2, is experimentally unknown. Its isomer, HBeCH, lies higher in energy, but has been detected by the infrared matrix isolation [J. Am. Chem. Soc. 1998, 120, 6097]. In the present study the ground and low-lying excited states of the BeCH2 and HBeCH isomers were investigated using state-of-the-art ab initio methods, including coupled-cluster theory with up to full quadruple excitations (CCSDTQ), and complete active space self-consistent field (CASSCF) with multireference configuration interaction with single and double excitations (MRCISD). The relative energies were obtained using the focal point analysis combined with large correlation-consistent cc-pCVXZ basis sets (X = D, T, Q, 5) and were extrapolated to the complete basis set (CBS) limit. The (3)B1 state of BeCH2 (C(2v) symmetry) is the global minimum on the ground triplet potential energy surface (PES). The (3)Σ(-) state of the linear isomer HBeCH is located 4.9 kcal mol(-1) above the global minimum, at the CCSDTQ/CBS level of theory. The BeCH2 and HBeCH isomers are connected through the (3)A" transition state lying 46.1 kcal mol(-1) above the global minimum. The higher-lying energy HBeCH structure has much larger Be-C bond dissociation energy (126.6 kcal mol(-1), cf. BDE(BeCH2) = 62.1 kcal mol(-1)). The lowest excited state of BeCH2 is the open-shell (1)B1 state, with a relative energy of only 4.9 kcal mol(-1) above the global minimum, followed by (1)A1 state (16.8 kcal mol(-1)) at the MRCISD/cc-pCVQZ level of theory. For the HBeCH isomer the lowest-energy excited states are (1)Δ and (1)Σ(+), lying about 30 kcal mol(-1) above the global minimum. For the ground state of BeCH2 the fundamental vibrational frequencies computed using second-order vibrational perturbation theory (VPT2) at the CCSD(T)/cc-pCVQZ level are reported. We hope that our highly accurate theoretical results will assist in the experimental identification of BeCH2.

Structures and transition states of Ge2CH2.

In this study a systematic theoretical investigation of Ge2CH2 is carried out. The singlet potential energy surface (PES) was explored using state-of-the-art theoretical methods including self-consistent field (SCF), coupled cluster theory incorporating single and double excitation (CCSD), perturbative triple [CCSD(T)] and full triples [CCSDT] with perturbative quadruple (Q), together with a variety of correlation-consistent polarized valence basis sets cc-pVXZ (where X = D, T, and Q). A total of eleven stationary points have been located on the Ge2CH2 singlet ground state PES. Among them, seven structures are minima (1S-7S), two are transition states (TS1 and TS2), and two are second-order saddle points (SSP1 and SSP2). The global minimum is predicted to be an exotic hydrogen-bridged structure 1S. The energy ordering of the seven minima (in kcal mol(-1)) obtained from focal point analysis using the extrapolation to complete basis set (CBS) limit with zero point vibrational energy (ZPVE), core correlation, diagonal Born-Oppenheimer (DBOC) and relativistic correction is 1S [0.0] < 2S [17.2] < 3S [18.3] < 4S [31.7] < 5S [39.9] < 6S [58.1] < 7S [82.1].

Optical anisotropy in packed isotropic spherical particles: indication of nanometer scale anisotropy in packing structure.

We investigated the origin of birefringence in colloidal films of spherical silica particles. Although each particle is optically isotropic in shape, colloidal films formed by drop drying demonstrated birefringence. While periodic particle structures were observed in silica colloidal films, no regular pattern was found in blended films of silica and latex particles. However, since both films showed birefringence, regular film structure patterns were not required to exhibit birefringence. Instead, we propose that nanometer-scale film structure anisotropy causes birefringence. Due to capillary flow from the center to the edge of a cast suspension, particles are more tightly packed in the radial direction. Directional packing results in nanometer-scale anisotropy. The difference in the interparticle distance between radial and circumferential axes was estimated to be 10 nm at most. Nanometer-scale anisotropy in colloidal films and the subsequent optical properties are discussed.

Validation of Web-based physical activity measurement systems using doubly labeled water.

BACKGROUND: Online or Web-based measurement systems have been proposed as convenient methods for collecting physical activity data. We developed two Web-based physical activity systems-the 24-hour Physical Activity Record Web (24hPAR WEB) and 7 days Recall Web (7daysRecall WEB). OBJECTIVE: To examine the validity of two Web-based physical activity measurement systems using the doubly labeled water (DLW) method. METHODS: We assessed the validity of the 24hPAR WEB and 7daysRecall WEB in 20 individuals, aged 25 to 61 years. The order of email distribution and subsequent completion of the two Web-based measurements systems was randomized. Each measurement tool was used for a week. The participants' activity energy expenditure (AEE) and total energy expenditure (TEE) were assessed over each week using the DLW method and compared with the respective energy expenditures estimated using the Web-based systems. RESULTS: The mean AEE was 3.90 (SD 1.43) MJ estimated using the 24hPAR WEB and 3.67 (SD 1.48) MJ measured by the DLW method. The Pearson correlation for AEE between the two methods was r = .679 (P < .001). The Bland-Altman 95% limits of agreement ranged from -2.10 to 2.57 MJ between the two methods. The Pearson correlation for TEE between the two methods was r = .874 (P < .001). The mean AEE was 4.29 (SD 1.94) MJ using the 7daysRecall WEB and 3.80 (SD 1.36) MJ by the DLW method. The Pearson correlation for AEE between the two methods was r = .144 (P = .54). The Bland-Altman 95% limits of agreement ranged from -3.83 to 4.81 MJ between the two methods. The Pearson correlation for TEE between the two methods was r = .590 (P = .006). The average input times using terminal devices were 8 minutes and 10 seconds for the 24hPAR WEB and 6 minutes and 38 seconds for the 7daysRecall WEB. CONCLUSIONS: Both Web-based systems were found to be effective methods for collecting physical activity data and are appropriate for use in epidemiological studies. Because the measurement accuracy of the 24hPAR WEB was moderate to high, it could be suitable for evaluating the effect of interventions on individuals as well as for examining physical activity behavior.

The lowest-lying electronic singlet and triplet potential energy surfaces for the HNO-NOH system: energetics, unimolecular rate constants, tunneling and kinetic isotope effects for the isomerization and dissociation reactions.

The lowest-lying electronic singlet and triplet potential energy surfaces (PES) for the HNO-NOH system have been investigated employing high level ab initio quantum chemical methods. The reaction energies and barriers have been predicted for two isomerization and four dissociation reactions. Total energies are extrapolated to the complete basis set limit applying focal point analyses. Anharmonic zero-point vibrational energies, diagonal Born-Oppenheimer corrections, relativistic effects, and core correlation corrections are also taken into account. On the singlet PES, the (1)HNO → (1)NOH endothermicity including all corrections is predicted to be 42.23 ± 0.2 kcal mol(-1). For the barrierless decomposition of (1)HNO to H + NO, the dissociation energy is estimated to be 47.48 ± 0.2 kcal mol(-1). For (1)NOH → H + NO, the reaction endothermicity and barrier are 5.25 ± 0.2 and 7.88 ± 0.2 kcal mol(-1). On the triplet PES the reaction energy and barrier including all corrections are predicted to be 7.73 ± 0.2 and 39.31 ± 0.2 kcal mol(-1) for the isomerization reaction (3)HNO → (3)NOH. For the triplet dissociation reaction (to H + NO) the corresponding results are 29.03 ± 0.2 and 32.41 ± 0.2 kcal mol(-1). Analogous results are 21.30 ± 0.2 and 33.67 ± 0.2 kcal mol(-1) for the dissociation reaction of (3)NOH (to H + NO). Unimolecular rate constants for the isomerization and dissociation reactions were obtained utilizing kinetic modeling methods. The tunneling and kinetic isotope effects are also investigated for these reactions. The adiabatic singlet-triplet energy splittings are predicted to be 18.45 ± 0.2 and 16.05 ± 0.2 kcal mol(-1) for HNO and NOH, respectively. Kinetic analyses based on solution of simultaneous first-order ordinary-differential rate equations demonstrate that the singlet NOH molecule will be difficult to prepare at room temperature, while the triplet NOH molecule is viable with respect to isomerization and dissociation reactions up to 400 K. Hence, our theoretical findings clearly explain why (1)NOH has not yet been observed experimentally.

1-Germavinylidene (Ge═CH2), germyne (HGeCH), and 2-germavinylidene (H2Ge═C) molecules and isomerization reactions among them: anharmonic rovibrational analyses.

Theoretical investigations of three equilibrium structures and two associated isomerization reactions of the GeCH(2) - HGeCH - H(2)GeC system have been systematically carried out. This research employed ab initio self-consistent-field (SCF), coupled cluster (CC) with single and double excitations (CCSD), and CCSD with perturbative triple excitations [CCSD(T)] wave functions and a wide variety of correlation-consistent polarized valence cc-pVXZ and cc-pVXZ-DK (where X = D, T, Q) basis sets. For each structure, the total energy, geometry, dipole moment, harmonic vibrational frequencies, and infrared intensities are predicted. Complete active space SCF (CASSCF) wave functions are used to analyze the effects of correlation on physical properties and energetics. For each of the equilibrium structures, vibrational second-order perturbation theory (VPT2) has been utilized to obtain the zero-point vibration corrected rotational constants, centrifugal distortion constants, and fundamental vibrational frequencies. The predicted rotational constants and anharmonic vibrational frequencies for 1-germavinylidene are in good agreement with available experimental observations. Extensive focal point analyses, including CCSDT and CCSDT(Q) energies and basis sets up to quintuple zeta, are used to obtain complete basis set (CBS) limit energies. At all levels of theory employed in this study, the global minimum of the GeCH(2) potential energy surface (PES) is confirmed to be 1-germavinylidene (GeCH(2), 1). The second isomer, germyne (HGeCH, 2) is predicted to lie 40.4(41.1) ± 0.3 kcal mol(-1) above the global minimum, while the third isomer, 2-germavinylidene (H(2)GeC, 3) is located 92.3(92.7) ± 0.3 kcal mol(-1) above the global minimum; the values in parentheses indicate core-valence and zero-point vibration energy (ZPVE) corrected energy differences. The barriers for the forward (1→2) and reverse (2→1) isomerization reactions between isomers 1 and 2 are 48.3(47.7) ± 0.3 kcal mol(-1) and 7.9(6.6) ± 0.3 kcal mol(-1), respectively. On the other hand, the barriers of the forward (2→3) and reverse (3→2) isomerization reactions between isomers 2 and 3 are predicted to be 55.2(53.2) ± 0.3 kcal mol(-1) and 3.3(1.6) ± 0.3 kcal mol(-1), respectively.

Real time observation and kinetic modeling of the cellular uptake and removal of silicon quantum dots.

The time courses of uptake and removal of silicon quantum dots (Si-QDs) by human umbilical endothelial cells (HUVECs) were observed via confocal laser scanning microscope. Si-QDs were internalized via endocytosis and transported to late endosomes/lysosomes. The number of internalized Si-QDs increased with time and gradually reached a plateau value. When Si-QD-internalized HUVECs were subsequently washed and exposed to fresh culture medium, HUVECs removed internalized Si-QDs via exocytosis. The number of internalized Si-QDs decreased with time and gradually reached a plateau value. Not all internalized Si-QDs were removed from the cell interior but large numbers of internalized Si-QDs remained accumulated inside cells. A kinetic model based on the mass balance of Si-QDs and receptors in a cell was proposed to describe the cellular uptake and removal of Si-QDs. Model calculation fitted well with experimental results. Using this model, the dissociation constant between receptors and Si-QDs in the endosome, K(d,in), was found to be a determinant factor for Si-QD accumulation in cells after the removal process.

Stau1 regulates Dvl2 expression during myoblast differentiation.

Post-transcriptional regulation of gene expression by RNA-binding proteins has pivotal roles in many biological processes. We have shown that Stau1, a conserved RNA-binding protein, negatively regulates myogenesis in C2C12 myoblasts. However, its target mRNAs in regulation of myogenesis remain unknown. Here we describe that Stau1 positively regulates expression of Dvl2 gene encoding a central mediator of Wnt pathway in undifferentiated C2C12 myoblasts. Stau1 binds to 3' untranslated region (UTR) of Dvl2 mRNA and Stau1 knockdown shortened a half-life of the mRNA containing Dvl2 3' UTR. After induction of myogenic differentiation, association of Stau1 with 3' UTR of Dvl2 mRNA was decreased. Correlated with the decrease in the association, the Dvl2 mRNA level was reduced during myogenesis. A forced expression of Dvl2 markedly inhibited progression of myogenic differentiation. Our results suggest that Dvl2 has an inhibitory role in myogenesis and Stau1 coordinates myogenesis through the regulation of Dvl2 mRNA.

Quadratically convergent algorithm for orbital optimization in the orbital-optimized coupled-cluster doubles method and in orbital-optimized second-order Møller-Plesset perturbation theory.

Using a Lagrangian-based approach, we present a more elegant derivation of the equations necessary for the variational optimization of the molecular orbitals (MOs) for the coupled-cluster doubles (CCD) method and second-order Møller-Plesset perturbation theory (MP2). These orbital-optimized theories are referred to as OO-CCD and OO-MP2 (or simply "OD" and "OMP2" for short), respectively. We also present an improved algorithm for orbital optimization in these methods. Explicit equations for response density matrices, the MO gradient, and the MO Hessian are reported both in spin-orbital and closed-shell spin-adapted forms. The Newton-Raphson algorithm is used for the optimization procedure using the MO gradient and Hessian. Further, orbital stability analyses are also carried out at correlated levels. The OD and OMP2 approaches are compared with the standard MP2, CCD, CCSD, and CCSD(T) methods. All these methods are applied to H(2)O, three diatomics, and the O(4)(+) molecule. Results demonstrate that the CCSD and OD methods give nearly identical results for H(2)O and diatomics; however, in symmetry-breaking problems as exemplified by O(4)(+), the OD method provides better results for vibrational frequencies. The OD method has further advantages over CCSD: its analytic gradients are easier to compute since there is no need to solve the coupled-perturbed equations for the orbital response, the computation of one-electron properties are easier because there is no response contribution to the particle density matrices, the variational optimized orbitals can be readily extended to allow inactive orbitals, it avoids spurious second-order poles in its response function, and its transition dipole moments are gauge invariant. The OMP2 has these same advantages over canonical MP2, making it promising for excited state properties via linear response theory. The quadratically convergent orbital-optimization procedure converges quickly for OMP2, and provides molecular properties that are somewhat different than those of MP2 for most of the test cases considered (although they are similar for H(2)O). Bond lengths are somewhat longer, and vibrational frequencies somewhat smaller, for OMP2 compared to MP2. In the difficult case of O(4)(+), results for several vibrational frequencies are significantly improved in going from MP2 to OMP2.

Selective labeling of the endoplasmic reticulum in live cells with silicon quantum dots.

A simple and novel approach was developed to obtain water-dispersible silicon quantum dots (Si-QDs) of low toxicity that were able to selectively label the endoplasmic reticulum (ER) in live cells. A block copolymer (Pluronic F127) was used to coat the surface of Si-QDs. Si-QDs form aggregates with diameters of 20-40 nm and show an outstanding optical stability upon UV irradiation. Our F127-treated Si-QDs would be a powerful tool for long-term real-time observation of the ER in live cells.

Anharmonic rovibrational analysis for disilacyclopropenylidene (Si2CH2).

The global minimum on the Si(2)CH(2) electronic singlet potential energy surface has been theoretically predicted to be a peculiar hydrogen bridged (Si···H···Si) disilacyclopropenylidene structure (Si(2)CH(2)). An accurate quartic force field for Si(2)CH(2) has been determined employing ab initio coupled-cluster theory with single and double excitations and a perturbative treatment for triple excitations [CCSD(T)], in combination with the correlation consistent core-valence quadruple zeta (cc-pCVQZ) basis set. The vibration-rotation coupling constants, equilibrium and zero-point vibration corrected rotational constants, centrifugal distortion constants, and harmonic and fundamental vibrational frequencies for six isotopologues of Si(2)CH(2) are predicted using vibrational second-order perturbation theory (VPT2). The anharmonic corrections for the vibrational motions involving the H bridged bonds are found to be more than 5% with respect to the corresponding harmonic vibrational frequencies. In this light, an experimental detection and characterization of disilacyclopropenylidene (Si(2)CH(2)) is highly desired.

The Beryllium tetramer: profiling an elusive molecule.

The structure and energetics of Be(4) are investigated using state-of-the-art coupled-cluster methods. We compute the optimized bond length, dissociation energy, and anharmonic vibrational frequencies. A composite approach is employed, starting from coupled-cluster theory with single, double, and perturbative triple excitations extrapolated to the complete basis set (CBS) limit using Dunning's correlation consistent cc-pCVQZ and cc-pCV5Z basis sets. A correction for full triple and connected quadruple excitations in the smaller cc-pCVDZ basis set is then added, yielding an approximation to CCSDT(Q)/CBS denoted c∼CCSDT(Q). Corrections are included for relativistic and non-Born-Oppenheimer effects. We obtain D(e) = 89.7 kcal mol(-1), D(0) = 84.9 kcal mol(-1), and r(e) = 2.043 Å. Second-order vibrational perturbation theory (VPT2) is applied to a full quartic force field computed at the c∼CCSDT(Q) level of theory, yielding B(e) = 0.448 cm(-1) and fundamental frequencies of 666 (a(1)), 468 (e), and 571 (t(2)) cm(-1). Computations on the spectroscopically characterized Be(2) molecule are reported for the purpose of benchmarking our methods. Perturbative estimates of the effect of quadruple excitations are found to be essential to computing accurate parameters for Be(2); however, they seem to exert a much smaller influence on the structure and energetics of Be(4). Our extensive characterization of the Be(4) bonding potential energy surface should aid in the experimental identification of this thermodynamically viable but elusive molecule.

From acetylene complexes to vinylidene structures: The GeC(2) H(2) system.

The expansion of germanium chemistry in recent years has been rapid. In anticipation of new experiments, a systematic theoretical investigation of the eight low lying electronic singlet GeC(2) H(2) stationary points is carried out. This research used ab initio self-consistent-field (SCF), coupled cluster (CC) with single and double excitations (CCSD), and CCSD with perturbative triple excitations [CCSD(T)] levels of theory and a variety of correlation-consistent polarized valence cc-pVXZ and cc-pVXZ-DK (Douglas-Kroll) (where X = D, T, and Q) basis sets. At all levels of theory used in this study, the global minimum of the GeC(2) H(2) potential energy surface (PES) is confirmed to be 1-germacyclopropenylidene (Ge-1S). Among the eight singlet stationary points, seven structures are found to be local minima and one structure (Ge-6S) to be a second-order saddle point. For the seven singlet minima, the energy ordering and energy differences (in kcal mol(-1) , with the zero-point vibrational energy corrected values in parentheses) at the cc-pVQZ-DK (Douglas-Kroll) CCSD(T) level of theory are predicted to be 1-germacyclopropenylidene (Ge-1S) [0.0 (0.0)] < vinylidenegermylene (Ge-3S) [13.9 (13.5)] < ethynylgermylene (Ge-2S) [17.9 (14.8)] < Ge-7S [37.4 (33.9)] < syn-3-germapropenediylidene (Ge-8S) [41.2 (37.9)] < germavinylidenecarbene (Ge-5S) [66.6 (61.6)] < nonplanar germacyclopropyne (Ge-4S) [67.8 (63.3)]. These seven isomers are all well below the dissociation limit to Ge ((3) P) + C(2) H(2) (X (1) Σ g+). This system seems particularly well poised for matrix isolation infrared (IR) experiments.

Low-lying triplet states of diphosphene and diphosphinylidene.

In this research, six low-lying triplet states of diphosphene (HPPH) and disphosphinylidene (PPH(2)) are systematically investigated starting from self-consistent field theory and proceeding to multireference coupled cluster methods using a wide range of basis sets. For each structure, the geometry, energy, dipole moment, harmonic vibrational frequencies, and infrared intensities are predicted. The triplet potential energy surface (PES) of P(2)H(2) is presented, based on systematically extrapolated coupled cluster energies and accounting for core-valence correlation, zero-point vibrational energy, and diagonal Born-Oppenheimer effects. Both (3)A'' pyramidal PPH(2) and (3)B skewed HPPH are minima on the triplet PES and lie 27.4 ± 0.3 and 32.4 ± 0.3 kcal mol(-1) above the global minimum structure closed-shell (1)A(g) trans-HPPH, respectively. The energy barrier for the isomerization reaction [(3)B skewed HPPH → (3)A'' pyramidal PPH(2)] is predicted to be 16.4 ± 0.3 kcal mol(-1). On this triplet PES, two equivalent (3)B skewed HPPH are converted via the (3)B(u) trans-HPPH transition state with a barrier of 9.1 ± 0.3 kcal mol(-1) or via the (3)B(2) cis-HPPH transition state with a barrier of 11.1 ± 0.3 kcal mol(-1). Moreover, the two equivalent (3)A'' pyramidal PPH(2) structures are connected through the (3)A(2) planar PPH(2) transition state with a barrier of 18.6 ± 0.3 kcal mol(-1). The energy crossing of the singlet and triplet adiabatic PES is studied using Mukherjee multireference coupled cluster method with the cc-pVQZ basis set, which predicts that the (3)B skewed HPPH is 1.4 kcal mol(-1) lower in energy than the corresponding (1)A skewed HPPH at the (3)B skewed HPPH optimized geometry.

Characterization of flowerlike silicon particles obtained from chemical etching: visible fluorescence and superhydrophobicity.

Flowerlike silicon particles are obtained by chemical etching of polycrystalline silicon polyhedrons using a mixture of hydrofluoric acid and nitric acid. The etched flowerlike particles show stable bright red photoluminescence under UV irradiation. The formation of pores with diameters of 3, 5.5, and 20 nm is revealed during etching. The etched particles exhibit superhydrophobic behavior with a contact angle of 158 degrees because of the sharp tips of their "petals". The source silicon polyhedrons are shown to possess radial grain boundaries. Preferential etching along the radial grain boundaries of the polyhedrons is thought to be the key reason for the formation of flowerlike porous silicon particles.

Unusual isomers of disilacyclopropenylidene (Si2CH2).

Nine electronic singlet state structures of Si(2)CH(2) have been systematically investigated by high level theoretical methods. This research employed coupled cluster (CC) methods with single and double excitations (CCSD) and CCSD with perturbative triple excitations [CCSD(T)] using the correlation-consistent polarized valence cc-pVXZ/cc-pV(X+d)Z (X = D, T, and Q) basis sets. Full valence complete active space self-consistent-field (CASSCF) wave functions were used for the interpretation of geometries and physical properties. Among the nine singlet stationary points, six structures (1S-6S) are found to be minima, two structures (7S and 8S) are transition states, and one structure (9S) is a second-order saddle point. The existence of the two peculiar hydrogen bridged isomers, 1S (Si...H...Si) and 4S (agostic CH...Si) is established. Extensive focal point analyses are used to obtain complete basis set (CBS) limit energies. For the six lowest-lying singlet minima, after focal point analyses, the energy ordering and energy differences (in kcal mol(-1), with the zero-point vibrational energy corrected values in parentheses) are predicted to be 1S [0.0 (0.0)] < 3S [14.7 (14.5)] < 4S [25.1 (25.3)] < 5S [28.2 (26.0)] < 6S [45.0 (45.4)] < 2S [73.8 (72.0)]. Their relative energies are strikingly different from those for the isovalent parent C(3)H(2) molecule. Geometries, dipole moments, harmonic vibrational frequencies, and associated infrared (IR) intensities are reported for all equilibrium structures.

Triplet states of cyclopropenylidene and its isomers.

The unique importance of the cyclopropenylidene molecule conveys significance to its low-lying isomers. Eleven low-lying electronic triplet stationary points as well as the two lowest singlet structures of C(3)H(2) have been systematically investigated. This research used coupled cluster (CC) methods with single and double excitations and perturbative triple excitations [CCSD(T)] and Dunning's correlation-consistent polarized valence cc-pVXZ (where X=D, T, and Q) basis sets. Geometries, dipole moments, vibrational frequencies, and associated infrared intensities of the targeted molecules have been predicted. The electronic ground state of cyclopropenylidene (3S, the global minimum) is the X (1)A(1) state with C(2v) point group symmetry. Among the 11 triplet stationary points, 7 structures are found to be minima, 2 structures to be transition states, and 2 structures to be higher-order saddle points. For the six lowest-lying triplet structures and singlet propadienylidene (2S), relative energies (zero-point vibrational energy corrected values in parentheses) with respect to the global minimum [ X (1)A(1) (3S)] at the cc-pVQZ-UCCSD(T) level of theory are predicted to be propynylidene (3)B(1aT)15.5(11.3)