Optical studies of the electronphonon interaction in the pyrene-PMDA complex

Low temperature phosphorescence spectra of pyrene-PMDA (pyromellitic acid dianhydride) imbedded in a naphthalene-PMDA host crystal are reported. The spectra exhibit resolved zero-phonon and multi-phonon structure which is significant since the phosphorescent state is characterized by ≈36% charge-transfer character. Several different phonons contribute to the structure with the dominant phonon having ground and excited state (from hot band analysis) frequencies of 25 and 15 cm^?1. The linear electronphonon coupling strength for the 25cm^?1 phonon is computed. This phonon is tentatively assigned to rotational motion of the rigid complex. Linewidth data yield a relaxation time of 0.4 ps at 2 K for the 25 cm^?1 phonon which is believed to be a pseudolocalized or resonant mode.     

Charge-transfer exciton transitions in anthracene-PMDA crystal

The reflection spectrum of the first singlet charge transfer transition of anthracene-PMDA (pyromellitic dianhydride) crystal has been obtained at temperatures close to 2 K. The spectrum is polarized along the stack axis and consists of a series of vibronic bands, approximately 500 cm^?1 wide, with impressed fine structure arising from intermolecular phonon modes. This fine structure is particularly prominent for the 00 band which starts with a zero-phonon line which is the most dominant feature of the entire spectrum. The zero-phonon line has a reflectivity of approximately 0.37 and a line width less than 5 cm^?1. This is the first time that an absolute reflection spectrum of a charge transfer transition with such vibronic details has been obtained. A preliminary discussion of the nature of the transition is presented.     

Mobility of mass-identified ions in neon and reaction rate coefficient for Ne+ + 2Ne → Ne+2 + Ne

The mobilities of mass-identified Ne⁺ and Ne⁺₂ ions in neon have been measured by the “four-gauze” electrical shutter method at 300°K. The reduced zero-field mobilities of Ne⁺ and Ne⁺₂ ions, corrected to 273°K, are 4.13± 0.04 and 6.20± 0.07 cm²V^?1sec^?1 respectively. The reaction rate coefficient for the termolecular ion-neutral association reaction is (4.6 ± 0.35) × 10^?32 cm⁶ sec^?1 and in the range from 2 to 10 V cm^?1 torr^?1 it does not depend on the electric field strength.     

Photoinitiated radical chains in solid polymeric methacrylates

Polymeric methacrylates functionalized with free methacryloyl groups are efficiently crosslinked in the presence of transition-metal carbonyls on UV irradiation of the polymeric solid. The reaction proceeds by a radical chain mechanism with a kinetic chain length of about 10 in a solvent-free polymer containing 10^?3 mole of methacryloyl groups per cm³. The chain length increases steeply when the glass transition of the polymer is reached, either by plastification or by an increase in temperature. The temperature dependence of the crosslinking yield below the glass transition is consistent with an activation energy of about 9 kcal mole^?1. The addition of acrylic monomers enhances chain propagation by up to an order of magnitude. Postirradiative crosslinking in the matrix comes to a standstill well before all acrylic groups or radicals have been exhausted: if, after cessation of the primary reaction, the matrix is briefly heated, a second crop of crosslinks is obtained without further exposure. The system behaves thus as if the radicals had been removed into traps from which they can be set free by thermal activation. From an analysis of the reaction kinetics it appears that in the glassy polymer 90% of the radicals are inactivated in this way. Radical recombination, however, is the principal mechanism of chain termination above the glass transition. From the kinetic data, diffusion coefficients for polymer-bound groups are found to be in the range of 10^?17–10^?16 cm² sec^?1 in the glassy polymer at room temperature. They are of the order of 10^?14 cm² sec^?1 in plasticized films above the glass transition.     

Oscillator strengths of the bands of the B̃2 A′1—X̃2 A″2 system of CD3 and a spectroscopic measurement of the recombination rate comparison with CH3

Absolute CD₃ concentrations were measured in the flash photolysis of d₆-HgMe₂. An oscillator strength of (0.99 ± 0.10) × 10^?2 was recorded for the 0O band of the B?—X? system, and a recombination rate coefficient of (4.9 ± 0.4) × 10^?11 cm³ molecule^?1 s^?1 was derived. It is suggested that the probability of recombination per collision is virtually the same as for the CH₃ radical.Some new bands of the B?—X? system have been discovered and tentatively assigned: from a study of the temperature dependence of the intensity of the 47300 cm^?1 transition, Herzberg's scheme ‘b’ has been established for the vibrational assignment.     

On the lower excited electronic states of glyoxal

The polarization of both nπ* absorption bands of glyoxal has been measured in a glass matrix of 2-methyltetrahydrofuran by the photoselection method. The second absorption band in the 30 000 cm^?1 region has been assigned to a ¹A_g → ¹B_g nπ* transition. Its intensity is mainly induced by interaction with the solvent. An absorption band at about 43 000 cm^?1 has been ascribed to a charge transfer transition in complexes of glyoxal and 2-MTHF.     

OH stretching frequencies of solid hydroxides and of free OH− ions

The vibrational frequency of free OH^? ions, which cannot be directly measured, has been claimed to be 3700 cm^?1. In solid hydroxides the OH stretching frequency has been found in the range from 3690 to 3100 cm^?1. The decrease of the vibrational frequency has been interpreted to be caused by hydrogen bridges or the increase of the metal oxygen bond strength. We suggest an alternative explanation. The vibrational frequency of unperturbed OH^? ions is 3570 ± 10 cm^?1. In ionic hydroxides this frequency is increased due to repulsion effects of the lattice or decreased if hydrogen bonds are present, to a large extent (up to 400 cm^?1) in the case of common OH^?….X bridges and only up to 70 cm^?1 in the case of XH….OH^? bonds.     

Nuclear magnetic relaxation dispersion measurement of water mobility at a silica surface

Nuclear magnetic relaxation rates are measured as a function of magnetic field strength corresponding to proton Larmor frequencies ranging from 0.01 to 42 MHz for silica gel samples with a nitroxide free radical covalently attached at the surface. The field dependence of the relaxation rate is interpreted using a translational model for the relaxation equation to yield a translational diffusion coefficient for the water, in the immediate vicinity of the radical attached to the surface, of 2.1 × 10^?6 cm² s^?1 at 278 K for Si-4000 silica.     

Thiopyrilium hexachlorostannate salts in short-circuited systems with an alkali metal

Organic semiconductors based on thiopyrilium hexachlorostannate salts with a conductivity of 10^?6 to 10^?2 S cm^?1 possess high electrochemical activity, which makes them promising materials for energy and information converters. When in contact with an alkali metal, they generate an emf due to the formation of a transition layer. The latter is an electronic dielectric, which ensures a stable emf and acts in an electric field as a unipolar conductor by the lithium and sodium cations. Cathodic-reduction products are shown to be solid electrolytes with conduction by the alkali metal and possess an electroconductivity of 10^?4 to 10^?3 S cm^?1 at 298 K. Chemical synthesis is used to insert the lithium and sodium cations in the salts and manufacture solid electrolytes with ionic conduction. The synthesized products are examined by methods of impedance, galvano-and potentiometry, spectroscopy, and x-ray diffraction and elemental analyses.     

Luminescent charge transfer of ground-state and metastable B+ ions

Endothermic charge-transfer reactions between B⁺(¹S and ³P) ions and several simple gases have been observed in a beam experiment at moderate and low energies. The products B(²S and ²D) were observed by means of their UV emission. Absolute cross sections for the four reaction channels were measured, ranging from 10^?21 to 10^?18 cm². The relative cross sections depend markedly on the collision partner, and are discussed in terms of system symmetry and schematic energy diagrams.     

Photorefractive performance of poly(triarylamine)‐Based polymer composites: An approach from the photoconductive properties

Photorefractive (PR) and photoconductive properties of methyl‐substituted poly(triarylamine) (PTAA) based PR composite is presented. PR composite consisted of PTAA, piperidinodicyanostyrene, (2,4,6‐trimethylphenyl)diphenylamine, and [6,6]‐phenyl‐C61‐butyric acid methyl ester. Photocurrent is simultaneously measured when a transient degenerate four wave mixing is recorded. Diffraction efficiency of 16.6%, response time of 5 ms, and sensitivity of 43 cm² J^?1 are measured under an applied field of 45 V μm^?1 and 632.8 nm illumination with the intensity of 1.5 W cm^?2. Response time of 10.2 ms with diffraction efficiency of 47.0% is obtained under a same field and 532 nm illumination with the intensity of 0.427 W cm^?2. Higher diffraction and faster response is due to the large photocurrent in the order of hundreds μA measured. The resultant trap density is in the order of 10¹⁴ cm^?3. Thus, space–charge field less than 1 V μm^?1 is evaluated, which limits the PR response. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 502–508     

Electronic and vibrational resonance Raman spectra of octamethyluranocene

The Raman spectrum of bis(tetramethylcyclo-octatetraene)uranium (U(TMCOT)₂), excited in resonance with its visible charge-transfer transitions shows an anomalously polarized electronic band at 473 cm^?1, twice as broad as the analogous band of uranocene, at 466 cm^?1. The broadening is attributed to crystal-field splitting associated with the lowered symmetry introduced by the methyl group, and/or a distribution of rotamer populations. Totally symmetric vibrational modes are observed at 879, 750, 580, 513 and 95 cm^?1; possible assignments are discussed.     

Die Feinstruktur in den Schwingungs- und elektronischen Absorptionsspektren von [CrO4]2− und [MnO4]−

Finestructure in the Vibrational and Electronic Absorption Spectra of [CrO₄]^2? and [MnO₄]^? The ir and ra spectra of Tl₂[CrO₄] and (C₂H₅)₄N[MnO₄] are measured and assigned. Details of the preresonance- and resonance-Raman effect are discussed. The exact knowledge of the vibrational spectrum enables the understanding of the complicated vibrational finestructure in the electronic absorption spectrum of (C₂H₅)₄N[MnO₄]. For the states of the charge-transfer t₁ → e* bands are found at 15 000, 15 170 cm^?1 for ¹T₁(I), at 17 646, 17 708, 17 809 cm^?1 for ¹T₂(II) and at 17 920, 17 992 and 18 080 cm^?1 for ³T₂(III). The electronic origin for the states of the t₂ → e* chargetransfer is at 24 661 for ¹T₁(IV) and 30 230 cm^?1 for ¹T₂(V). The vibrational coupling is only with the totally symmetric Mn? O-stretching-vibration. Bands at 29 500 cm^?1 and 44 450 cm^?1 are assigned to the ¹T₂-states of the t₁, t₂ → t₂* charge-transfer.     

Singlet—triplet absorption spectrum of 9,10-dichloroanthracene crystal

The T₁ ← S_O absorption spectrum of 9,10-dichloroanthracene single crystal was measured by observing delayed fluorescence. The transition dipole is perpendicular to the molecular plane. The absorption coefficient at 694 nm is estimated to be 1 × 10^?3 cm^?1.     

Tunable biode laser high resolution spectroscopy of the ν3 vibration of matrix isolated SO2

True lineshape of the ν₃(b₁) vibrational transition of ³²SO₂ isolated in an Ar matrix was measured with a high resolution (< 10^?3 cm^?1) tunable diode laser spectrometer and temperature effects on line frequencies and linewidths are reported.     

1H NMR utilization of through-space effects in configurational assignments. I—application to nitriles; determination of the separate effects of the electric field and anisotropy of the CN group

The changes in chemical shift induced by isomerization for all the ring protons of the Z- and E-5,5-dimethyl-2-cyclohexenylidene acetonitriles depend only on the through-space effects of the cyano group. The configurational assignments were made taking into consideration the anisotropic and electric field effects, either separately or together. In the first case, the total effects are Δ_XCN^T=?14.7×10^?6cm³ mol^?1 and bμ_CN^T=14.7×10^?30 cm³, respectively. The second approach allows the estimation of the values Δ_XCN=?4.9 × 10^?6 cm³ mol^?1 and bμ_CN=9.8 × 10^?3 cm³, reflecting the combined contributions of magnetic anisotropy and electric field to the total effect.     

Time-resolved infrared spectroscopic study of the orientation behavior of liquid crystalline molecules in the presence of an electric field

Time-resolved Fourier-transform infrared spectroscopy is used to follow the changes induced by electric field in molecular orientation of a 4-n-pentyl-4′-cyanobiphenyl (5CB) liquid crystal. At an electric field strength greater than 600 V cm^?1, the long axis of a 5CB molecule orientates to the direction of the electric field. The orientation function, however, saturates at a field strength greater than 1000 V cm^?1. The relaxation time of the rise amd decay processes was in the range of 0.04–0.24 s and a decreased with increasing field strength. The orientation/relaxation process is discussed on the basis of the motion of liquid crystal domains.     

Rates of Proton Abstraction from Conjugated Dienes in the Gas Phase

The rates of proton transfer from 2, 4-hexadiene, 1, 3-cycloheptadiene, cyclopentadiene and acetone to t-butoxide have been measured in the gas phase using pulsed-ion-cyclotron-resonance spectroscopy. The rate constants are (units of 10^?10 cm³ molecule^?1 s^?1): 2.7 ± 0.4, 3.8 ± 0.4, 6.1 ± 0.7 and 10.8 ± 1.5, respectively. These results are analyzed in terms of the properties of the encounter complex and reaction transition states. The reaction profile for t-butoxide + cyclopentadiene is modeled using RRKM theory and an estimate for the central barrier height is obtained.     

Low-temperature absorption spectrum of the VO43− ion in single crystals of Ca2PO4CI

Polarized absorption spectra of single crystals of Ca₂PO₄Cl doped with V(V) ions have been measured at liquid-helium temperature. Only one broad and very intense band is observed from 30000 to 45000 cm^?1. In T_d symmetry it is assigned as a charge-transfer transition ¹T₂ ← ¹A₁. Under theT_d→ D_2d site perturbation, the excited state ¹T₂ is split into ¹B₂ and ¹E.     

Near-IR photorefractive composites based on oxidized single-wall carbon nanotubes

The photoelectric, nonlinear optical, and photorefractive characteristics of polymer composites made from unplasticized polyvinylcarbazole (PVK) and single-wall carbon nanotubes containing surface oxygen groups (at C:O ratio of 77.8:22.2%) were analyzed. The dependences of the quantum efficiency of charge-carrier generation on the applied electric field E measured at 1064 and 1550 nm coincide and are approximated by the Onsager equation expanded to the E ⁴ term, at π₀ = 0.012 and r ₀ = 9.8 Å. The third-order optical nonlinearity determined by the EFISH technique at a nanotube content of 0.26 wt % is 2 × 10⁵ pm²/V² or 2.3 × 10^?29 C⁴ m/J³ in SI units. The pattern of photorefractive kinetic curves indicates that the mean free path of holes is longer than the mean range of electrons. The photorefractive net gain coefficient of the signal beam measured at 1064 nm in a field of E = 170 V/μm is Γ ? α = 55 cm^?1 (α = 10 cm^?1 is the optical absorption coefficient at 1064 nm). At 1550 nm, the net gain coefficient measured in a field of E = 265 V/μm is Γ ? α = 55.7 cm^?1 (α = 3.3 cm^?1 at 1550 nm). In the presence of oxygen groups, there is no transfer of electrons photogenerated in carbon nanotubes to the external acceptor C⁶⁰. This effect can be associated with an increase in the ionization potential of nanotubes by almost 0.8 eV as a result of oxidation.