UV-induced protonation of molecules adsorbed on ice surfaces at low temperature

UV irradiation of ice films adsorbed with methylamine molecules induces protonation of the adsorbate molecules at low temperature (50-130 K). The observation indicates that long-lived protonic defects are created in the ice film by UV light, and they transfer protons to the adsorbate molecules via tunneling mechanism at low temperature. The methylammonium ion formed by proton transfer remains to be stable at the ice surface. It is suggested that this solid-phase protonation might play a significant role in the production of molecular ions in interstellar clouds.     

The raman spectrum of hexachlorobutadiene

Summary The conjugation of the two double bonds in hexachlorobutadiene leads to shortening of the C-C and C=C bonds, i.e., to a certain contraction of the whole molecule.     

Symmetry effects in the electronic spectrum of ammonia at low temperature

A band intensity alternation has been observed in the absorption spectra to the à ¹A state of NH₃ and ND₃ cooled in supersonic expansions. The nuclear statistical explanation for this interesting effect is given here.     

The low temperature infrared spectrum of solid cyclopropylcyanide

The infrared spectrum of solid cyclopropyl cyanide at −196°C was recorded from 4000 to 400 cm⁻¹. The observed data are not in accord with an assignment of the normal vibrations suggested earlier. A few reassignments are proposed on the basis of the new infrared data and the results of a recent Raman study.     

The raman spectrum and structure of dicyclopentadienylberyllium

The Raman spectra of solid and liquid dicyclopentadienylberyllium are described. They suggest the presence of two π-bonded rings in the molecule, one pentahapto and one polyhapto coordinated to the Be atom.     

The low temperature Fourier Transform Raman spectrum of polystyrenes

In a previous paper (Jones and Wesley, Spectrochimica Acta 47A (9/10), 1293 (1991)) the Fourier Transform (FT) Raman spectra of various polystyrenes were presented and differences in the spectra in terms of the configuration, conformation and crystallinity of the samples were discussed. In this paper the low temperature FT Raman spectra of polystyrenes are presented. The differences between the spectra as a function of temperature and crystallinity are discussed. It is clear that, although lowering the temperature is advantageous in improving the quality of the spectra, crystallinity is the key to quality in the spectra. Isomeric purity alone seems to be far less advantageous. It is proposed that the band near 1000 cm⁻¹ in this system can be used to estimate the crystallinity. The paper concludes with some comments on the very slow crystallization rate of typical isotactic polystyrene.     

Plasmon-assisted click chemistry at low temperature: an inverse temperature effect on the reaction rate

Plasmon assistance promotes a range of chemical transformations by decreasing their activation energies. In a common case, thermal and plasmon assistance work synergistically: higher temperature results in higher plasmon-enhanced catalysis efficiency. Herein, we report an unexpected tenfold increase in the reaction efficiency of surface plasmon-assisted Huisgen dipolar azide–alkyne cycloaddition (AAC) when the reaction mixture is cooled from room temperature to −35 °C. We attribute the observed increase in the reaction efficiency to complete plasmon-induced annihilation of the reaction barrier, prolongation of plasmon lifetime, and decreased relaxation of plasmon-excited-states under cooling. Furthermore, control quenching experiments supported by theoretical calculations indicate that plasmon-mediated substrate excitation to an electronic triplet state may play the key role in plasmon-assisted chemical transformation. Last but not least, we demonstrated the possible applicability of plasmon assistance to biological systems by AAC coupling of biotin to gold nanoparticles performed at −35 °C.

The decrease of reaction temperature can potentially lead to an increase of plasmon-assisted catalytic efficiency.     

Doping of fullerite with molecular oxygen at low temperature and pressure

Two methods are described for doping of fullerite C₆₀ with molecular oxygen at a pressure of ∼104 Pa and at temperature 20–30 °C. It was found by mass spectrometry using oxygen ¹⁸O as dopant that a portion of molecular oxygen absorbed by the pre-decontaminated fullerite (first method) is removed as CO and CO₂ at the heating temperature ≤200 °C. Doping during fullerite precipitation from the liquid phase (second method) makes it possible to prepare samples with the oxygen content ≥1.2 at.%. The fullerite doped with oxygen to this level is diamagnetic. The paramagnetic properties of an O₂ molecule disappear when O₂ is incorporated into the fullerene lattice. This is interpreted on the basis of quantum chemical calculations as a sequence of equilibrium formation of the adduct C₆₀O₂. Calculations showed that the subsequent chemical transformation of C₆₀O₂ resulting in the O-O bond cleavage is energetically favorable, enabling prerequisites for the formation of products of incomplete (CO) and deep (CO₂) oxidation of fullerene under mild conditions. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 662–671, April, 2006     

The resonance inverse raman effect

Multichannel photoelectric detection has been employed to record the inverse Raman spectrum of a number of organic liquids. The enhanced resonance effect has been shown to operate and is proposed as a method for detecting low molecular concentrations.     

The overtone oh stretching raman spectrum of liquid water

The very weak Raman spectrum of liquid water has been measured in the overtone OH stretching region. The similarity of tlie observed spectrum to the overtone infrared spectrum, and the weak spectral dependence of the depolarization ratio is in sharp contrast to the fundamental spectra.     

The question of a pressure effect in the reaction OH + CO at room temperature

Absolute rate constants for the reaction of OH with CO were determined at 296 ± 2 K, with 50 torr of He and 0–350 torr of SF₆. The rate constant was found to change from ≈1.0 × 10¹¹ to ≈1.9 × 10¹¹ cm³ mol^?1 s^?1 depending on the pressure and nature of the third body M, in agreement with our earlier results and with the three studies by Heicklen, Cox, Calvert, and their co-workers. However, it is not possible, at present, to attribute the effect with certainty to any particular cause.     

A new approach to the analysis of the effect of dissolved salts on the raman spectrum of water

The evolution of the Raman spectrum of water in the OH stretching region vs concentration of dissolved NaI, NaBr, NaBF₄ and NaClO₄ is investigated. The analysis of the intrinsically overlapping spectral components is accomplished by Fourier deconvolution. Particular attention is paid to the behaviour of the component arising from the anion—water interaction.     

HCl adsorption on ice at low temperature: a combined X-ray absorption, photoemission and infrared study

The reaction of HCl on water ice provides a simple case for understanding dissociation and proton transfer in this non-optimal, incomplete solvation environment, playing a central role in atmospheric chemistry. This reaction has been repeatedly reported as thermally dependent, whereas the theoretical models predict a spontaneous dissociation. We examine the adsorption of HCl on ice at low temperature (50 K and 90 K) via a combination of near-edge X-ray absorption spectroscopy (NEXAFS) at the chlorine L-edge, photoemission (XPS and UPS), and reflection-adsorption infrared spectroscopy (FT-RAIRS). We show the complete dissociation of HCl into Cl(-) and H(+) through 3 hydrogen bonds, predominantly by direct reaction with water (80%) and by self-solvation (20%), in full agreement with the prediction of a barrierless process.     

苯酚分子拉曼光谱的密度泛函理论研究

采用B3LYP杂化泛函,6-31++G(d,p)基组,对苯酚分子的结构进行了优化.通过频率计算,获得了苯酚分子的拉曼光谱,并利用势能函数分布(PED)对拉曼光谱进行了指认.绘制了苯酚分子的静电势分布图,讨论了苯酚分子发生化学反应的位置,同时计算了HOMO-LUMO的能级差.通过TD-DFT计算获得了苯酚分子的吸收光谱和激发态.     

Band structure of the four pentacene polymorphs and effect on the hole mobility at low temperature

The band structure of the four known polymorphs of pentacene is computed from first principles using the accurate molecular orbitals of the isolated molecule as the basis for the calculation of the crystalline orbitals. The computed bands are remarkably different for each polymorph, but their diversity can be easily rationalized using a simple analytical model that employs only three parameters. The effect of the electronic structure on the hole mobility was evaluated using a simple model based on the constant relaxation time approximation. It is found that the mobility tensor is highly anisotropic for three of the four considered polymorphs. The practical implication of this prediction on the technology of thin-film organic transistors is discussed.     

The effect of electrolyte additives on the rate performance of hard carbon anode at low temperature for lithium-ion capacitor

Lithium-ion capacitor (LIC), which combines the advantages of lithium-ion battery (LIB) and electrical double layer capacitor (EDLC), has a rapid development during last decade, however, the poor low temperature performance still limits its application. In this paper, three electrolyte additives including vinylene carbonate (VC), fluoroethylene carbonate (FEC) and 1,3,2-dioxathiolane 2,2-dioxide (DTD) have been utilized and their effects on the rate performance of hard carbon (HC) anode of LIC at various temperatures ranging from 25 °C to ?40 °C have been well evaluated. The cell containing FEC shows the best rate performance at various temperatures and has the charge and discharge capability even at ?40 °C. For HC anode, the charge transfer impedance (R_CT) increases exponentially at low temperature, while the equivalent series resistance (Rs) and the impedance of solid electrolyte interface (SEI) increase relatively few. At low temperatures, the effect of FEC may be mainly reflected in its effect on the charge transfer process.     

Thermodynamic states of nanoclusters at low pressure and low temperature: the case of 13 H(2)

A confinement model of finite-size systems that embodies an equation of state is presented. The temperature and pressure of the system are obtained from the positions and velocities of the enclosed particles after a number of molecular dynamics simulations. The pressure has static and dynamic (thermal) contributions, extending the Mie-Gru?neisen equation of state to include weakly interacting anharmonic oscillators. The model is applied to a system of 13 H(2) molecules under low-pressure and low-temperature conditions in the classical regime. The confining cage in this case is a spherical hydrogen cavity. The Born-Oppenheimer molecular dynamics in conjunction with density functional theory are used for the time evolution of the particle system. The hydrogen molecules form a noncrystalline cluster structure with icosahedral symmetry that remains so in the whole temperature range investigated. The fluctuations of the interatomic distances increase with the temperature, while the orientational order of the enclosed system of molecules fades out, suggesting a gradual order-disorder transition.     

The time-resolved resonance raman spectrum of pulse radiolytically produced phenoxyl radical

The time-resolved resonance-enhanced Raman spectrum of phenoxyl radical has been observed at microsecond times in pulse radiolysis experiments. Raman b     

The effect of dimerization on the resonance raman excitation profiles of metalloporphyrins

Model calculations are reported showing the effect of dimerization on the absorption spectra and resonance Raman excitation profiles of metalloporhyrins. This effect, which qualitatively resembles that of metal atom substitution or solvent change, is mainly due to mixing of the monomer Q and B states.