Accurate Geometry and Non-Covalent Interactions in 1-Phenylethanol and its Monohydrate: A Rotational Study

The pure rotational spectra of 1-phenylethanol and its monohydrate were measured by using a pulsed jet Fourier transform microwave spectrometer. One conformer of the 1-phenylethanol monomer with the trans form was observed in the pulsed jet. The experimental values of rotational constants of ten isotopologues, including eight mono-substituted ¹³C and one D isotopologues, allow an accurate structure determination of the skeleton of 1-phenylethanol. For its monohydrate, only one isomer has been observed, of which 1-phenylethanol adopts the trans form and binds with water through an O−H⋅⋅⋅O_w and an O_w−H⋅⋅⋅π hydrogen bond. Each rotational transition displays a doublet with a relative intensity ratio of 1 : 3, due to a hindered internal rotation of water around its C₂ axis. This study provides the information on accurate geometry of 1-phenylethanol (PE) and large amplitude motion of water in the PE monohydrate.     

The multiphoton ionization spectrum of toluene in a supersonic free jet: internal rotation of the methyl group

The S₁← S_o electronic transitions of toluene involving also some internal rotational levels were observed for the first time in the multiphoton ionization spectrum in a supersonic jet. A large population in several low-lying internal rotational levels and a strong coupling between electronic motion and the internal rotation are suggested.     

Laser-induced-fluorescence study of A Na/Na2 free jet. II. State-dependent effective inelastic cross sections for rotational and vibrational relaxation

Laser-induced-fluorescence measurements along the jet axis are used to study the relaxation of Na₂ molecules in a Na/Na₂ expansion. From the fluorescence intensity, the evolution of the occupancies of several vibration—rotation levels of the Na₂ ground state is obtained. The whole relevant region along the jet axis is covered: from the equilibrium region close to the nozzle down to the downstream part of the jet, where the internal-state distribution is non-Boltzmann and “frozen”. The relaxation of Na₂ molecules is analysed using first-order relaxation equations. Vibrational and rotational relaxation are treated separately by means of similar equations but with different inelastic cross sections determining the relaxation rates. The evolution of the vibrational levels can be described by means of a single effective cross section of = 100 Ų; the rotational cross sections are strongly J-state dependent and range from = 250 to 15 Ų, for J = 13-55.     

Molecular structure of van der Waals complex of o- and m-methylaniline with CF3Cl, CF3H, CF4 and CH4 studied by laser induced fluorescence spectroscopy and ab initio calculations

The excitation LIF spectra of van der Waals complexes of o- and p-methylaniline and CF₃Cl, CF₃H, CH₄ and CF₄ in a supersonic free jet are reported. The spectra show a resolved structure characteristic due to the internal rotational transitions of the methyl group. The equilibrium geometries in the ground state of the complexes have been calculated at MP2/6-31+G^∗ level of calculation and the intermolecular interaction have been discussed.     

Hydrogen/argon plasma jet with methane addition

Spatial distributions of plasma parameters are presented for a H₂/Ar plasma jet with addition of methane. The plasma has been generated at atmospheric pressure by a 200 A (20 kW) nontransferred do arc. Optical emission spectroscopy has been used for the measurements assuming the plasma jet to be optically thin and to have an axial symmetry. Local spectral ernissivity values have been evaluated using a routine Abel inversion procedure. Half- width and emissivity of H spectral line have been measured to determine the electron density and temperature of the plasma. The densities of excited C, CH radicals have been evaluated from the absolute emissivities of relevant molecular emission bands measured in limited spectral intervals in the visible spectrum. The emissivity ratios have been used to fund rotational and vibrational temperatures. The results supply information on methane decomposition and the behavior of molecular radicals in close-to-thermal plasma jets.     

Co(υ ⩽ 3, J ⩽ 9) vibrational and rotational freezing along supersonic free jets

Spontaneous infrared fluorescence has been used to measure the rovibrational populations (υ ⩽ 3, J ⩽ 9) of CO along supersonic free jets. The CO molecules are vibrationally excited (T_V > 3000 K) before the expansion, in a cw electric glow discharge. Vibrational and rotational freezings are detected successively. The effect of the background gas in the free jet is also illustrated.     

光腔衰荡光谱研究PH2自由基在465-555nm的光谱

Absorption spectra of jet-cooled PH₂ radicals were recorded in the wavelength range of 465-555 nm using cavity ringdown spectroscopy. The PH₂ radicals were produced in a supersonic jet by pulsed direct current discharge of a mixture of PH₃ and SF₆ in argon. Seven vibronic bands with fine rotational structures have been observed and assigned as 0⁰₀、2ⁿ₀、2ⁿ₁(n=1-3) bands of the ?²A₁- Χ²B₁ electronic transition. Rotational assignments and rotational term values for each band were re-identified, and the molecular parameters including rotational constants, centrifugal distortion constants, and spin-rotation interaction constants were also improved with reasonably high precision. In addition, large perturbations observed in each quantum number of total angular momentum of the a axis level of the excited vibronic stateswere briefly discussed.     

Step-scan Fourier transform infrared absorption spectroscopy of liquid benzene cluster in a pulsed supersonic jet

We have obtained the infrared absorption spectrum of the jet-cooled C₆H₆ in the 800–5000 cm⁻¹ region using step-scan Fourier transform infrared spectrometer combined with a pulsed supersonic jet system. The experimental spectrum was in good agreement with the convolution spectrum of the monomer band with the rotational temperature of ∼37 K and the broadbands of liquid C₆H₆, indicating the first spectroscopic evidence for the formation of supercooled liquid C₆H₆ cluster in the supersonic jet.     

Rotational and vibrational temperatures of naphthalene in a naphthalene-argon supersonic jet

In the $\text{A}$¹B_2u-$\text{X}$¹A_g system of naphthalene in a supersonic jet, rotational contour calculations show rotational temperatures of 2–60 K for argon carrier gas pressures of 1520-120 Torr. The b_1u vibration v₂₄ shows a high vibrational temperature which corresponds to the seeding temperature for pressures <400 Torr.     

Mercury-rare gas van der Waals complexes: From the lightest HgHe to the heaviest HgXe

Mercury helium and mercury xenon van der Waals complexes have been observed in a supersonic free jet expansion by laser-induced fluorescence in the vicinity of the Hg(³P₁¹S₀) transition. The helium complex very weakly bonded in the ground state (D₀ = 8 ± 1 cm⁻¹) exhibited a simple rotational structure. The strongly bonded xenon complex has shown a clear example of isotopic broadening in its vibronic spectra.     

Conformational relaxation of S-(+)-carvone and R-(+)-limonene studied by microwave Fourier transform spectroscopy and quantum chemical calculations

S-(+)-carvone (C₁₀H₁₄O, 5-isopropenyl-2-methylcyclohex-2-en-1-one) and R-(+)-limonene (C₁₀H₁₆, 4-isopropenyl-1-methylcyclohexene) have been characterized in the gas phase using a Fourier transform microwave spectrometer coupled to a supersonic molecular beam. Two conformers—with the isopropenyl group in the equatorial position—have been detected for each compound and described by a set of molecular parameters including the principal rotational constants and the quartic centrifugal distortion parameters. Quantum chemical calculations indicate that a third conformer might not be observed due to relaxation processes in the jet. The gas phase results are compared with the liquid phase IR-Raman-VCD spectra.     

How CO2 Interacts with Carboxylic Acids: A Rotational Study of Formic Acid–CO2

The rotational spectra of the 1:1 formic acid–carbon dioxide molecular complex and of its monodeuterated isotopologues are analysed in the 6.5–18.5 and 59.6–74.4 GHz frequency ranges using a pulsed jet Fourier transform microwave spectrometer and a free‐jet absorption millimetre wave spectrometer, respectively. Precise values of the rotational and quartic centrifugal distortion constants are obtained from the measured frequencies, and quadrupole coupling constants are determined from the deuterium hyperfine splittings. Structural parameters are estimated from the moments of inertia and their differences among isotopologues: the complex has a planar structure with the two subunits held together by a HC(O)OH???O=C ? O (2.075 Å) and a HC(OH)O???CO₂ (2.877 Å) interactions. The ab initio intermolecular binding energy, obtained at the counterpoise corrected MP2/aug‐cc‐pVTZ level of calculation, is D_e=17 kJ mol^?1.     

Electronic spectra of 2-acetylanthracene

The electronic spectrum of 2-acetylanthracene in a supersonic free jet reveals the existence of two rotational isomers with ≈ 196 cm⁻¹difference between their S₁ origins. In low-temperature rigid glasses, 2-acetylanthracene forms stable dimers. The probable structure of this dimer is also briefly discussed.     

Emission spectra of supersonically cooled dimethyldiacetylene cations

The ā²E_u → X?²E_g emission spectra of 2,4-hexadiyne (dimethyldiacetylene) cation and its d₃- and d₆-deuterated analogues were excited by electron impact on a seeded helium supersonic free jet. Vibrational analyses are made and vibrational frequencies in both states are inferred to ±1 cm^-1. Spin-orbit splittings are observed especially in degenerate overtone bands. The observed rotational contours allow a partial rotational analysis.     

Study of singlet—triplet coupling in glyoxal by level anticrossing spectroscopy. V. Nature of singlet—triplet interaction

We observe in glyoxal cooled in a supersonic free jet the fluorescence of individual rotational levels of the S₁ state excited by a cw laser. We use the technique of singlet—triplet magnetic resonance near an anticrossing to measure matrix elements V₃₁ as a function of rotational quantum numbers N_s, N_t, K_s, K_t. The experimental results are compared with theoretical models of singlet—triplet couplings and we show that the spin-vibronic interaction is the dominant singlet—triplet interaction in glyoxal.     

Water–Water and Water–Solute Interactions in Microsolvated Organic Complexes

A structural study of microsolvated clusters of β‐propiolactone (BPL) formed in a pulsed molecular jet expansion is presented. The rotational spectra of BPL–(H₂O)_n (n=1–5) adducts have been analyzed by broadband microwave spectroscopy. Unambiguous identification of the structures has been achieved using isotopic substitution and experimental measurements of the cluster dipole moment. The observed structures are discussed in terms of the different intermolecular interactions between water molecules and between water and BPL, which include n–π* interactions involving the lone pairs of electrons on water oxygen atoms and the antibonding orbital of the BPL carbonyl group. The changes induced in the structures of the water hydrogen‐bonding network by complexation to BPL indicate that water clusters adopt specific configurations to maximize their links to solute molecules.     

Electrostatic fiber spinning from polymer melts. II. Examination of the flow field in an electrically driven jet

The flow field in an electrically driven jet has been examined and quantitatively analyzed. Using a model fluid, the nature of the streamlines and magnitude of the stream velocities were investigated with the aid of tracer particle photography. It was found that the velocity field is not purely extensional, but contains rotational components as well. Furthermore, the only portion of the jet completely free of any rotational component is the region about the symmetry axis. The extensional strain rate along the symmetry axis increases rapidly with the applied electric field intensity and can attain values in excess of 50 sec^?1. This suggests that it might be possible to draw continuous oriented fibers from polymer melts by this technique if the jet can be operated at sufficiently high electric field intensity.     

Fluorine Substitution Effects on Flexibility and Tunneling Pathways: The Rotational Spectrum of 2‐Fluorobenzylamine

The effect of ring fluorination on the structural and dynamical properties of the flexible model molecule 2‐fluorobenzylamine has been studied by rotational spectroscopy in free‐jet expansion and quantum chemical methods. The complete potential energy surface originating from the flexibility of the aminic side chain has been calculated at the B3LYP/6‐311++G** level of theory and the stable geometries were also characterized with MP2/6‐311++G**. The rotational spectra show the presence of two of the predicted four stable conformers: the global minimum (I), in which the side chain’s dihedral angle with the phenyl plane is almost perpendicular, is stabilized by an intramolecular hydrogen bond between the fluorine atom and one hydrogen of the aminic group; and a second conformer II (E_II?E_I≈5 kJ mol^?1) in which the dihedral angle is smaller and the amino group points towards the aromatic ortho hydrogen atom. This conformation is characterized by a tunneling motion between two equivalent positions of the amino group with respect to the phenyl plane, which splits the rotational transition. The ortho fluorination increases, with respect to benzylamine, the tunneling splitting of this motion by four orders of magnitude. The motion is analyzed with a one‐dimensional flexible model, which allows estimation of the energy barrier for the transition state as approximately 8.0 kJ mol^?1.     

A comparative study of jet formation in nozzle‐ and nozzle‐less centrifugal spinning systems

Centrifugal spinning, a recently developed approach for ultra‐fine fiber production, has attracted much attention as compared with the electrospinning, due to its high yield, no solution polarity and high‐voltage electrostatic field requirements, etc. In this study, the jet formation process and spinning parameters on jet path are explored and compared in nozzle‐ and nozzle‐less centrifugal spinning systems. For nozzle‐less centrifugal spinning, fingers are formed at the front of thin liquid film due to the theory of Rayleigh–Taylor instability. We find that the lower solution concentration and higher rotational speed favor the formation of thinner and longer fingers. Then, the critical angular velocity and initial jet velocity for nozzle‐/nozzle‐less centrifugal spinning are obtained in accordance with the balance of centrifugal force, viscous force, and surface tension. When jet leaves the spinneret, it will undergo a series of motions including necking and whipping processes, and then, a steady spiral jet path is formed with its radius getting tighter. Finally, we experimentally study the effect of rotational speed and solution concentration on jet path, which shows that the higher rotational speed results in a larger radius of jet path while the solution concentration has little effect on it. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1547–1559     

Skeletal Torsion Tunneling and Methyl Internal Rotation: The Coupled Large Amplitude Motions in Phenyl Acetate

The rotational spectrum of phenyl acetate, CH₃COOC₆H₅, is measured using a free jet absorption millimeter-wave spectrometer in the range from 60 to 78 GHz and two pulsed jet Fourier transform microwave spectrometers covering a total frequency range from 2 to 26.5 GHz. The features of two large amplitude motions, the methyl group internal rotation and the skeletal torsion of the CH₃COO group with respect to the phenyl ring C₆H₅ (tilted at about 70°), characterize the spectrum. The vibrational ground state is split into four widely spaced sublevels, labeled as A0, E0, A1, and E1, each of them with its set of rotational transitions and with additional interstate transitions. A global fit of the line frequencies of the four sublevels leads to the determination of 51 spectroscopic parameters, including the ΔE_A0/A1 and ΔE_E0/E1 vibrational splittings of ~36.4 and ~33.5 GHz, respectively. The V₃ barrier to methyl internal rotation (~136 cm⁻¹) and the skeletal torsion B₂ barrier to the orthogonality of the two planes (~68 cm⁻¹) are deduced.