Millimeter-wave and high-resolution infrared spectroscopy of the low-lying vibrational states of pyridazine isotopologues.

The gas-phase rotational spectrum from 8 to 750 GHz and the high-resolution infrared (IR) spectrum of pyridazine (o-C4H4N2) have been analyzed for the ground and four lowest-energy vibrationally excited states. A combined global fit of the rotational and IR data has been obtained using a sextic, centrifugally distorted-rotor Hamiltonian with Coriolis coupling between appropriate states. Coriolis coupling has been addressed in the two lowest-energy coupled dyads (ν16, ν13 and ν24, ν9). Utilizing the Coriolis coupling between the vibrational states of each dyad and the analysis of the IR spectrum for ν16 and ν9, we have determined precise band origins for each of these fundamental states: ν16 (B1) = 361.213 292 7 (17) cm-1, ν13 (A2) = 361.284 082 4 (17) cm-1, ν24 (B2) = 618.969 096 (26) cm-1, and ν9 (A1) = 664.723 378 4 (27) cm-1. Notably, the energy separation in the ν16-ν13 Coriolis-coupled dyad is one of the smallest spectroscopically measured energy separations between vibrational states: 2122.222 (72) MHz or 0.070 789 7 (24) cm-1. Despite ν13 being IR inactive and ν24 having an impractically low-intensity IR intensity, the band origins of all four vibrational states were measured, showcasing the power of combining the data provided by millimeter-wave and high-resolution IR spectra. Additionally, the spectra of pyridazine-dx isotopologues generated for a previous semi-experimental equilibrium structure (reSE) determination allowed us to analyze the two lowest-energy vibrational states of pyridazine for all nine pyridazine-dx isotopologues. Coriolis-coupling terms have been measured for analogous vibrational states across seven isotopologues, both enabling their comparison and providing a new benchmark for computational chemistry.

Vibrationally excited states of 1H- and 2H-1,2,3-triazole isotopologues analyzed by millimeter-wave and high-resolution infrared spectroscopy with approximate state-specific quartic distortion constants.

In this work, we present the spectral analysis of 1H- and 2H-1,2,3-triazole vibrationally excited states alongside provisional and practical computational predictions of the excited-state quartic centrifugal distortion constants. The low-energy fundamental vibrational states of 1H-1,2,3-triazole and five of its deuteriated isotopologues ([1-2H]-, [4-2H]-, [5-2H]-, [4,5-2H]-, and [1,4,5-2H]-1H-1,2,3-triazole), as well as those of 2H-1,2,3-triazole and five of its deuteriated isotopologues ([2-2H]-, [4-2H]-, [2,4-2H]-, [4,5-2H]-, and [2,4,5-2H]-2H-1,2,3-triazole), are studied using millimeter-wave spectroscopy in the 130-375 GHz frequency region. The normal and [2-2H]-isotopologues of 2H-1,2,3-triazole are also analyzed using high-resolution infrared spectroscopy, determining the precise energies of three of their low-energy fundamental states. The resulting spectroscopic constants for each of the vibrationally excited states are reported for the first time. Coupled-cluster vibration-rotation interaction constants are compared with each of their experimentally determined values, often showing agreement within 500 kHz. Newly available coupled-cluster predictions of the excited-state quartic centrifugal distortion constants based on fourth-order vibrational perturbation theory are benchmarked using a large number of the 1,2,3-triazole tautomer isotopologues and vibrationally excited states studied.

Millimeter-Wave and High-Resolution Infrared Spectroscopy of 2-Furonitrile─A Highly Polar Substituted Furan.

The rotational spectrum of 2-furonitrile (2-cyanofuran) has been obtained from 140 to 750 GHz, capturing its most intense rotational transitions at ambient temperature. 2-Furonitrile is one of two isomeric cyano-substituted furan derivatives, both of which possess a substantial dipole moment due to the cyano group. The large dipole of 2-furonitrile allowed over 10 000 rotational transitions of its ground vibrational state to be observed and least-squares fit to partial octic, A- and S-reduced Hamiltonians with low statistical uncertainty (σfit = 40 kHz). The high-resolution infrared spectrum, obtained at the Canadian Light Source, allowed for accurate and precise determination of the band origins of its three lowest-energy fundamental modes (ν24, ν17, and ν23). Similar to other cyanoarenes, the first two fundamental modes (ν24, A″, and ν17, A', for 2-furonitrile) form an a- and b-axis Coriolis-coupled dyad. More than 7000 transitions from each of these fundamental states were fit to an octic A-reduced Hamiltonian (σfit = 48 kHz), and the combined spectroscopic analysis determines fundamental energies of 160.1645522 (26) cm-1 and 171.9436561 (25) cm-1 for ν24 and ν17, respectively. The least-squares fitting of this Coriolis-coupled dyad required 11 coupling terms, Ga, GaJ, GaK, GaJJ, GaKK, Fbc, FbcJ, FbcK, Gb, GbJ, and FacK. Using both the rotational and high-resolution infrared spectra, a preliminary least-squares fit was obtained for ν23, providing its band origin of 456.7912716 (57) cm-1. The transition frequencies and spectroscopic constants provided in this work, when combined with theoretical or experimental nuclear quadrupole coupling constants, will provide the foundation for future radioastronomical searches for 2-furonitrile across the frequency range of currently available radiotelescopes.

Computational and infrared spectroscopic investigations of N-substituted carbazoles.

The carbazole moiety is a commonly identified structural motif in the high-molecular-weight components of petroleum, known as asphaltenes. Detailed characterization of carbazoles is important for understanding the structure of asphaltenes and addressing challenges in the areas of heavy oil recovery, transportation, upgrading, and oil spills, arising from asphaltene properties and composition. In this work we study carbazole and the four N-substituted carbazoles 9-methylcarbazole, 9-ethylcarbazole, 9-vinylcarbazole and 9-phenylcarbazole. Experimental far- and mid-infrared spectra of these five carbazoles are measured using transmission and photoacoustic techniques. The molecular structures of the monomers and the respective dimers, optimized at the ωB97X-D/6-311++G(d,p) level of the density functional theory (DFT), are subjected to harmonic vibrational frequency calculations. The effect of changing substituents on the N-H bond, π-π stacking distances, and angles between monomers within the dimers, in addition to intermolecular interactions, is investigated. Noncovalent interaction analysis is employed to highlight the areas of attractive and repulsive interactions in the dimers. Thermochemistry calculations show that the formation of dimers of all carbazoles is spontaneous at 298 K. Comparison of the calculated vibrational spectra of these compounds with experimental spectra indicates that the existence of both monomers and dimers must be invoked to account for the observed bands in the infrared spectra. Excellent correlations between the experimentally-determined and calculated harmonic vibrational energies are obtained, with an experimental-to-calculated scaling factor of 0.95-0.96. These findings highlight the coupled computational-experimental approach for the interpretation of vibrational spectra and are essential for improving the spectroscopic characterization of N-substituted carbazoles.

High-resolution FTIR spectroscopy of benzaldehyde in the far-infrared region: probing the rotational barrier.

A discrepancy between theoretical and experimental values of the rotational barrier in benzaldehyde has been observed, which was attributed to inaccurate experimental results in part. Here, we report results on the -CHO torsion of benzaldehyde (C6H5CHO) based on a high resolution spectroscopic investigation in the far-infrared range in an effort to remove the experimental ambiguity. The rotationally-resolved vibrational spectra were measured with an unapodized resolution of 0.00064 cm-1 using synchrotron-based Fourier transform infrared (FTIR) spectroscopy at the Canadian Light Source. The torsional fundamental νt = 109.415429(20) cm-1 was unambiguously assigned via rovibrational analysis, followed by the tentative assignment of the first (2νt-νt) and second (3νt- 2νt) hot bands at 107.58 cm-1 and 105.61 cm-1, respectively, by comparison of the observed Q branch structures at high resolution with simulation based on a previous microwave study. This assignment is different from any previous low resolution infrared studies in which the intensity patterns were misleading. The key result of the assignment of the first three transitions allowed the determination of the barrier to internal rotation of (hc)1533.6 cm-1 (4.38 kcal mol-1). When compared with calculated results from vibrational second-order perturbation theory (VPT2) and the quasiadiabatic channel reaction path Hamiltonian (RPH) approach, the experimental value is still too low and this suggests that the discrepancy between theory and experiment remains despite the best experimental efforts.

Observation of pressure-induced electron transfer in SnC2O4.

We examined the high pressure behavior of stannous oxalate via Raman and X-ray absorption spectroscopy (XAS) inside a diamond anvil cell. Phase transitions were observed to occur near 2.6 and 15 GPa which were reversible upon decompression to ambient conditions. When further pressurized above 15 GPa, the colorless material sustains irreversible chemical alterations and becomes bright red colored - darkening at higher pressures. Another irreversible phase transition occurred above 20 GPa. Concomitant with color change of the sample, we observed a softening of the ν(C-C) modes of the C2O42- anion via Raman spectroscopy. We performed a separate XAS experiment which indicates that the Sn2+ cation undergoes a partial reduction of the 2+ oxidation state with pressure which persists when the sample was depressurized to ambient conditions. Thus, electron density within the C-C bond in the oxalate anion appears to migrate toward the tin cation with pressure. This observation suggests that pressure can offer a very controllable means to vary cation-anion and unit cell dimensions (and thus the electric interactions causing electron movement) and thus the pressure-induced synthesis of novel materials.

Correspondence bias of Chinese and American undergraduates: similar initial trait attributions but different situational corrections.

Correspondence bias (CB) refers to individuals' tendency to make trait inferences regarding the constrained behavior of others. To investigate the influences of the attitude diagnosticity of behavior and situational constraints on CB in a cross-cultural context, a sample of 357 Chinese undergraduates (140 males, 39.2%) aged 17-27 years old (M age = 21.13, SD = 1.94) and 252 American undergraduates (111 males, 44%) aged 16 to 24 years old (M age = 20.39, SD = 1.70) took part in a modified attitude attribution task. The results of analysis of covariance showed that (a) Americans and Chinese undergraduates produced similar patterns in which CB decreased with the attitude diagnosticity of behavior, while (b) only Chinese undergraduates' CB decreased as situational constraints increased. These results indicated that the initial trait attributions were similar for individuals in America and China, but there were cultural differences in the stage with situational constraints.

Sb- and Bi-doped Mg2Si: location of the dopants, micro- and nanostructures, electronic structures and thermoelectric properties.

Due to increasing global energy concerns, alternative sustainable methods to create energy such as thermoelectric energy conversion have become increasingly important. Originally, research into thermoelectric materials was focused on tellurides of bismuth and lead because of the exemplary thermoelectric properties of Bi2Te3 and PbTe. These materials, however, contain toxic lead and tellurium, which is also scarce and thus expensive. A viable alternative material may exist in Mg2Si, which needs to be doped and alloyed in order to achieve reasonable thermoelectric efficiency. Doping is a major problem, as p-type doping has thus far not produced competitive efficiencies, and n-type doping is problematic because of the low solubility of the typical dopants Sb and Bi. This investigation shows experimentally that these dopants can indeed replace Si in the crystal lattice, and excess Sb and Bi atoms are present in the grain boundaries in the form of Mg3Sb2 and Mg3Bi2. As a consequence, the carrier concentration is lower than the formal Sb/Bi concentration suggests, and the thermal conductivity is significantly reduced. DFT calculations are in good agreement with the experimental data, including the band gap and the Seebeck coefficient. Overall, this results in competitive efficiencies despite the low carrier concentration. While ball-milling was previously shown to enhance the solubility of the dopants and thus the carrier concentration, this did not lead to enhanced thermoelectric properties.

Pressure induced phase transitions and metallization of a neutral radical conductor.

The crystal structure and charge transport properties of the prototypal oxobenzene-bridged 1,2,3-bisdithiazolyl radical conductor 3a are strongly dependent on pressure. Compression of the as-crystallized α-phase, space group Fdd2, to 3-4 GPa leads to its conversion into a second or ß-phase, in which F-centering is lost. The space group symmetry is lowered to Pbn21, and there is concomitant halving of the a and b axes. A third or γ-phase, also space group Pbn21, is generated by further compression to 8 GPa. The changes in packing that accompany both phase transitions are associated with an "ironing out" of the ruffled ribbon-like architecture of the α-phase, so that consecutive radicals along the ribbons are rendered more nearly coplanar. In the ß-phase the planar ribbons are propagated along the b-glides, while in the γ-phase they follow the n-glides. At ambient pressure 3a is a Mott insulator, displaying high but activated conductivity, with σ(300 K) = 6 × 10(-3) S cm(-1) and E(act) = 0.16 eV. With compression beyond 4 GPa, its conductivity is increased by 3 orders of magnitude, and the thermal activation energy is reduced to zero, heralding the formation of a metallic state. High pressure infrared absorption and reflectivity measurements are consistent with closure of the Mott-Hubbard gap near 4-5 GPa. The results are discussed in the light of DFT calculations on the molecular and band electronic structure of 3a. The presence of a low-lying LUMO in 3a gives rise to high electron affinity which, in turn, creates an electronically much softer radical with a low onsite Coulomb potential U. In addition, considerable crystal orbital (SOMO/LUMO) mixing occurs upon pressurization, so that a metallic state is readily achieved at relatively low applied pressure.