Determination of the temperature and pressure dependence of the reaction OH + C2H4 from 200-400 K using experimental and master equation analyses

The pressure and temperature dependence for the reaction of OH + C(2)H(4) was studied over the range of conditions: 200-400 K and 5-600 Torr by laser flash photolysis, laser-induced fluorescence (FP-LIF). Additional experiments were conducted at room temperature by laser flash photolysis, cavity ring-down spectroscopy to facilitate determination of the high pressure limit. One-dimensional master equation calculations were conducted to test the temperature and pressure dependence of the reaction in He and in N(2). The energetics of the reaction and geometries of intermediate species were calculated by ab initio calculations (DFT-BH&HLYP/6-311+G(3df,2p) and CBS-APNO level along DFT-IRC, respectively. An investigation into the importance of a pre-reaction van der Waals complex on the kinetics over the pressure range of the troposphere is discussed. The high pressure rate coefficient was extracted by fitting the master equation calculations to the data and yields k(infinity) = 5.01 x 10(-12) exp(148/T) cm(3) molecule(-1) s(-1). The master equation calculations were then optimized for the pressure fall-off in He and N(2) by varying the average downward energy transfer parameter (DeltaE(down)) for the different collision partners and finally fitted to a Troe expression to determine k(o) and F(cent) for use in atmospheric modeling.     

Online analysis of products from a direct ethanol fuel cell

Methodology for the online analysis of the main products from a direct ethanol fuel cell (DEFC) has been developed. The liquid exhaust from the fuel cell is first passed through a conductivity cell to determine the concentration of acetic acid and then CO₂ is extracted into a nitrogen stream for determination with a flow-through infrared-based CO₂ sensor. The other major product, acetaldehyde can be obtained by difference from the current. The continuous measurement of these products allows monitoring of changes in product distributions with time and operating conditions, resulting in a simple online system for rapid evaluation of anode catalysts in DEFCs.     

Ultrafast noncollinear optical parametric chirped pulse amplification in KTiOAsO4

Amplification of femtosecond pulses at 1.56 microm based on noncollinear parametric chirped pulse amplification in a potassium titanyl arsenate (KTA) crystal with pumping at 1.05 microm is reported. The 100 fs pulses of an erbium fiber laser are parametrically amplified while synchronously pumped by an amplified mode-locked Nd:YLF laser. This amplifier has a saturated gain of 65 dB with 30% conversion efficiency and has produced 160 fs pulses with peak powers of up to 0.75 GW. The system produced 380 mW before compression and can be readily scaled to the multiwatt range with bandwidths to support sub-100 fs pulses.     

High-energy handling capabilities of optical fibers: Application to pulse compression and direct generation of megawatt picosecond pulses

The compression of the output of a Q-switched, mode-locked Nd:YAG (130 ps, 1.06 m) is reported for a number of different core-size single mode, multimode and polarization preserving fibers at power levels near the damage threshold. In maximizing the energy throughput, the main limitations are dielectric breakdown and nonlinear induced birefringence. Compressed pulse stability is found to depend critically on core size at this power level. An optimized compressor has been obtained capable of compression factors up to 35 (3.7 ps) with peak power in excess of 2 MW. Second-harmonic generation has been observed in polarization preserving fibers.     

Kinetic study of the reactions of the sodium dimer (Na2) with a range of atmospheric species

The reactions of Na(2) with a series of atmospheric constituents were studied using a fast flow tube with detection of Na(2) by laser induced fluorescence at 656.2 nm [Na(2)(A(1)Sigma(+)(u) - X(1)Sigma(+)(g))]. The resulting rate coefficients at 298 K for the reactions of Na(2) with OH, O(2), NO(2), NO, O(3), H, H(2) and H(2)O are: (1.01(+0.35)(-0.25)) x 10(-10), (2.95 +/- 0.46) x 10(-11), (1.79(+0.51)(-0.31)) x 10(-10), (1.33 +/- 0.16) x 10(-11), (8.0(+24)(-3.0)) x 10(-11), < or =6 x 10(-12), 相似文献   

Supramolecular main chain liquid crystalline polymers utilizing azopyridine derivatives

A series of main chain liquid crystalline polymers were formed through intermolecular hydrogen bonding between a functionalized bisazopyridine phenol and aromatic bisacids. The behaviour of these complexes was studied through differential scanning calorimetry and thermal polarizing optical microscopy. The presence of the hydrogen bonds was confirmed through infrared spectroscopy. These complexes formed thermotropic mesophases. The phases were determined to be nematic in nature from the schlieren textures of the optical micrographs. As the length of flexible spacer groups separating the mesogenic portions increased, the clearing temperatures of the mesophases decreased. As the length of the rigid component increased, the clearing temperature increased. A new bisacid species based on 2-hydroxy-6-naphthoic acid was used to increase clearing temperatures while remaining within an acceptable temperature window.