Cis-trans isomerization of iodine-doped polyacetylene

A quantitative analysis of the cis—trans isomerization of the lightly doped polyacetylene with iodine at room temperature is reported. The cis—trans ratio was determined on the basis of the infrared absorption measurement. The result clearly demonstrates the promotion of the isomerization with increase in the dopant concentration. The degree of the amount of the isomerization, however, is rather small compared with the previous study based on the nuclear magnetic resonance measurement.     

Microwave spectral study of 2-fluorophenol: cis conformer

The microwave spectra of 2-fluorophenol and its deuterated species have been observed and analyzed in the frequency ranges 12.5–18.0 GHz (KU band) and 21.5–26.0 GHz (K band) in the ground vibrational state at room temperature. For the normal species, the radio frequency-microwave double resonance spectrum has been recorded in the frequency range 30.0–38.0 GHz. Three rotational and five quartic centrifugal distortion constants for the normal species, $\text{A}\text{?}\text{= 3337.86 ± 0.02}$, $\text{B}\text{?}\text{= 2231.92 ± 0.01}$, $\text{C}\text{?}\text{= 1337.52 ± 0.01}$, d_J = (3.5 ± 2.9) × 10^?4, d_JK = (?4.9 ± 1.5) × 10^?3, d_K = (?3.2 ± 1.0) × 10^?3, d_WJ = (?2.0 ± 1.0) × 10^?7, d_WK = (2.6 ± 0.8) × 10^?6 (in MHz), and three rotational constants for the deuterated species, $\text{A}\text{?}\text{= 3324.70 ± 0.03}$, $\text{B}\text{?}\text{= 2177.95 ± 0.03}$, $\text{C}\text{?}\text{= 1315.96 ± 0.03}$ (in MHz), have been obtained. Consideration of the r_s coordinate of the hydroxyl hydrogen atom leads to the assignment of the spectra to the cis conformer of the molecule. An r₀ structure for the cis conformer has been proposed. The nonbonded OH ? F distance is lower by about 0.3 Å than the sum of the van der Waals radii.     

A multichannel Raman spectrometry study of polyacetylene isomerization induced by laser irradiation

The multichannel Raman spectrometry has been used in the study of the isomerization reaction of an 80% cis PA film into a trans PA, using a laser beam for a double purpose. It is employed simultaneously as an activation agent inducing the isomerization reaction and the Raman diffusion. In each experience, the power of the laser beam Pⁱ(λ) was equivalent to the temperature. Twelve spectra have been recorded at different time periods tj = j·dt. The integrations of the Raman intensities related to two selected bands were numerically calculated.We also proposed an original method for the determination of the isomeric composition. A quantitative relationship between the equilibrium temperature and the laser beam power (in the range of laser power: 30 < Pⁱ(λ) < 300 mW) has been found. An estimate number of isomerized molecules N₀ and then a correction factors f_cis and f_trans were also obtained.     

Photochemical preparation of nitrosomethanol: Vibrational frequencies,force field,and normal coordinate analysis of the cis and trans isomers

The previously unknown molecule C-nitrosomethanol [H₂C(OH)(NO)] and seven of its isotopic modification [¹³C, ¹⁸OH, ¹⁵N, D₃, D₃-¹⁵N, H₂C(OD)(NO), and HDC(OH)(NO)] have been photolytically prepared from the corresponding methylnitrite isotopes in a low-temperature argon matrix. By irradiating methylnitrite into its $\text{S}{}_1\text{(nπ}{}^1\text{← S}{}_0$ transition at 365 nm, the molecule is transformed into a hydrogen-bonded 1:1 complex between formaldehyde and nitroxyl. Photolysis of this complex produces either the trans (λ_exc = 345 nm) or the cis (λ_exc ≥ 645 nm) isomer of nitrosomethanol. Selective photoisomerization processes permit interconversion of the conformers (cis → trans with λ_exc = 510 nm and trans → cis with λ_exc ≥ 645 nm). The ir spectra (40–170 cm^?1) of cis- and trans-nitrosomethanol were measured and analyzed in conjunction with a normal coordinate analysis based on a constrained valence force field (transferable valence force field approach). The frequencies of cis- and trans-nitrosomethanol were assigned and their force fields determined.     

Peierls distortion in trans polyacetylene: Evidence from infrared intensities

It is shown that from the polarization properties of the infrared spectrum of oriented pristine trans polyacetylene clear evidence of Peierls distortion is obtained. Moreover, it is shown that during CH stretching and in-plane bending CC bonds develop relevant charge fluxes. Infrared intensity studies indicate the existence of an unusual charge mobility.     

Far infrared optical properties of MoCl5 doped CIS polyacetylene

Far infrared transmission spectra of MoCl₅ homogeneously doped polyacetylene are reported. They show that in this spectral range the optical index is frequency independent but increases strongly with increasing doping level. IR conductivity is compared to d.c. conductivity.     

Solid-state lithium/polyacetylene battery

A solid-state lithium/iodine battery has been formed by directly contacting metallic lithium with iondine-doped polyacetylene. The procedure is similar to that used for the well-known lithium/iodine-polyvinylpyridine system. The advantage of the system proposed here may be related to the extraordinary electrical properties of polyacetylene which, when doped with iodine, acquires a very high electrical conductivity over a wide range of halogen concentration.     

Vibrational analysis of the Raman spectra of polycrystalline cis-2-butene

The vibrational assignments and potential energy distributions for cis-2-butene were examined by transferring appropriate force constants from trans-2-butene and the model systems, cis-1,2- and trans-1,2-difluoroethylene. The model fluoroethylene systems provided both the crucial interaction force constants, which account for effects across the double bond in cis-2-butene, and the skeletal out-of-plane force constants. The zero-order frequencies calculated for cis-2-butene from the transferred potential function agreed quite well with the low temperature Raman spectra of the polycrystalline material.     

Vibrational spectroscopy of trans and cis deuterated formic acid (HCOOD): Anharmonic calculations and experiments in argon and neon matrices

The absorption spectra of trans and cis conformers of deuterated formic acid (HCOOD) isolated in argon and neon matrices are analyzed in the mid-infrared and near-infrared spectral regions (7900-450 cm⁻¹). Vibrational excitation by narrow-band IR radiation is used to convert the lower-energy trans conformer to the higher-energy cis form. A large number of overtone and combination bands are identified. The results of anharmonic vibrational calculations (CC-VSCF) for both conformers are reported and compared to the experimental spectra.     

cis Acrolein: Mixing of the S0 and S1 electronic states by the (a″) skeletal torsional vibration

Large effects of vibronic coupling upon vibrational levels of the ground (¹A′) and first excited (¹A″) singlet electronic states of cis acrolein (2-propenal) are successfully modeled. Some implications for CH₂CHCHO spectroscopy and photophysics are discussed briefly.     

Vibrational analysis of ethylamines: Trans and gauche forms

Starting from force constant values calculated by an ab initio MO method ($\text{4-31G(N}{}^1\text{)}$), and by adjusting the diagonal elements, a practical force constant matrix (F) has been reached which could explain the observed infrared and Raman spectra (in the frequency range lower than 2000 cm^?1) of the gauche form of the ethylamine CH₃CH₂NH₂ molecule and five isotopic species CH₃¹³CH₂NH₂, CH₃CH₂¹⁵NH₂, CH₃CD₂NH₂, CH₃CH₂ND₂, and CD₃CD₂NH₂. The F matrix for the trans form of ethylamine was constructed by transferring ab initio $\text{4-31G(N}{}^1\text{)}$ values and by revising diagonal elements with conversion factors whose values are equal to the corresponding values of gauche form. A nearly complete set of assignments was achieved of the vibrational bands of ethylamines, observed so far in the spectral range 2000–100 cm^?1. In matrix isolation spectroscopy, two bands assignable to the NH₂ wagging vibrations of gauche and trans forms have been found at 775 and 782 cm^?1, respectively, for CH₃CH₂NH₂. They are at 768 and 774 cm^?1, respectively, for CD₃CD₂NH₂. From the intensity changes of these bands observed on changing the nozzle temperature in the matrix formation, the energy difference ΔE (gauche-trans) of these two conformers has been estimated to be 100 ± 10 cm^?1.     

Exafs study of FeCl3-doped polyacetylene

FeK absorption spectra of FeCl₃-doped polyacetylene [CH(FeCl₃)_y]_x having y values of 0.024, 0.087 and 0.13, were measured by use of synchrotron radiation. The analyses of observed EXAFS data showed that Fe atom is surrounded by about four Cl atoms with Fe-Cl distance of 2.18–2.20 Å. It is concluded that the dopant exists mainly in the form of FeCl₄^-, and the following reaction takes place in the FeCl₃ doping process. 2FeCl₃ + e^- → FeCl₄^- + FeCl₂     

The microwave spectrum of cis-2-pentene

The microwave spectrum of cis-2-pentene has been shown to originate from molecules in the skew-conformation (dihedral angle φ = 119 ± 3°). From A-E doublet splittings the barrier to internal rotation about the C₁C₂ axis was found to be 280 ± 4 cm^?1; furthermore the dipole moment components and centrifugal distortion constants are reported. In excited states of the C₃C₄ torsion the spectra exhibit further splittings; these are due to tunneling between the two equivalent skew-conformations through a barrier of 210 ± 20 cm^?1.     

Theoretical study of cisplatin adsorption on silica

The adsorption of cisplatin and its complexes, cis-[PtCl(NH₃)₂]⁺ and cis-[Pt(NH₃)₂]²⁺, on a SiO₂(1 1 1) hydrated surface has been studied by the Atom Superposition and Electron Delocalization method. The adiabatic energy curves for the adsorption of the drug and its products on the delivery system were considered. The electronic structure and bonding analysis were also performed. The molecule-surface interactions are formed at expenses of the OH surface bonds. The more important interactions are the Cl-H bond for cis-[PtCl₂(NH₃)₂] and cis-[PtCl(NH₃)₂]⁺ adsorptions, and the Pt-O interaction for cis-[Pt(NH₃)₂]²⁺ adsorption. The Cl p orbitals and Pt s, p y d orbitals of the molecule and its complexes, and the s H orbital and, the s and p orbitals of the O atoms of the hydrated surface are the main contribution to the surface bonds.     

An ab initio study of the in-plane harmonic force fields and fundamental vibration frequencies of cis- and trans-1,3-butadiene

The structure, in-plane force field, and fundamental vibration frequencies of trans- and cis-1,3-butadiene are calculated ab initio using the 4-31G basis set. Using a scaling procedure based on computational results from smaller molecules, the vibration frequencies for the trans-conformer calculated from the ab initio force constant matrix are found on average to be within 2.2% of the experimental values “harmonized” according to Dennison's rule. The values predicted for the cis-conformer, for which experimental spectroscopic data are only now becoming available, should facilitate the complete in-plane assignment of fundamentals in the near future.     

Phase-shift analysis of π N → K Σ

We have performed an energy-independent phase-shift analysis of πN → KΣ by analyzing differential cross-section and polarization data for the reactions π⁺p → K⁺∑⁺ and

at fifteen energies from threshold to 2137 MeV invariant mass. The single-energy solutions were linked by shortest-path methods with and without constraints implied by the Odorico zeros for the reaction π^?p → K⁺Σ^?. Similar to π^?p → KΛ it has been found that both isostates are dominated below 1900 MeV by resonances in the spin $\text{1}\text{2}$ waves. The F₃₇ resonance couples to KΣ with √x_πNx_KΣ= 0.04.     

Band structure of polyacetylene, (CH)x

The one-electron energy bands and densities of states of polyacetylene in both cis- and trans-conformations have been investigated. The principal issue addressed is whether the itinerant picture alone is sufficient to explain the experimental properties of this material. We conclude that the one-electron model provides an excellent zeroth-order explanation of current observations of optical and transport effects in both pure and doped forms of this unusual polymer.     

Rotational Spectra of cis-HCOOH, trans-HCOOH, and trans-HCOOH

While the rotational spectrum of trans-HCOOH is well known, the cis-rotamer was known previously only from a few microwave transitions. The spectra of cis- and trans-HCOOH and of trans-H¹³COOH have been identified in the far infrared Fourier transform spectrum recorded in the range 20-100 cm⁻¹. The measurements were performed using an 80-cm base length White-type multipass absorption cell in combination with a Bruker IFS 120 HR spectrometer. The White cell was set up for 90 passes (total path length=72 m) and the spectrum was measured with a resolution (FWHM) of 0.0012 cm⁻¹. Submillimeter-wave transitions, just under 1 terahertz, of the same three species of formic acid were measured in the range from 835 to 993 GHz (27.8-33.1 cm⁻¹) and it was possible to assign b-type Q-branch transitions of both cis- and trans-HCOOH in this region, and also transitions of trans-H¹³COOH. These measurements served furthermore as a check on the calibration of the FTIR measurement. Furthermore, new millimeter-wave measurements in the range 172-366 GHz were made, bridging the gap between the MW and FIR lines for cis-HCOOH and providing important data for trans-H¹³COOH. The assigned FTIR, submillimeter- and millimeter-wave data reported in this work were fitted together with previously published rotational transitions to obtain rotational constants, using Watson's A-reduced Hamiltonian, for cis-HCOOH, trans-HCOOH, and trans-H¹³COOH.     

Stability of polyacetylene films

The oxidative and radiation stability of polyacetylene films have been determined. The radiation stability of the material is found to be quite good but the intrinsic thermal oxidative stability is poor and presents a serious obstacle to widespread terrestrial or space use.