Theoretical study of the photodesorption mechanism of nitric oxide on a Ag(111) surface: a nonequilibrium Green's function approach to hot-electron tunneling

The photoinduced desorption of NO molecules on a Ag surface was studied theoretically using a recently developed method based on the nonequilibrium Green's function approach combined with the density functional theory. Geometry optimizations for the stable NO dimer phase were carried out, and two structures of adsorbed dimers were identified. We calculated the reaction probabilities as a function of incident photon energy for each of the dimers and compared them with experimental action spectra. The two main features of the action spectra, (i) a long tail to the long wavelength (approximately 600 nm) and (ii) a rapid increase at approximately 350 nm, were well reproduced. By theoretical analysis, we found the importance of quantum interference for the interfacial charge transfer between the metal substrate and the adsorbate, as well as the contribution of secondary electrons. Our calculations suggest that the photoactive species is dimeric and that the resonant level is single for the photodesorption of NO.     

Kinetic study of the ClOO + NO reaction using cavity ring-down spectroscopy

Cavity ring-down spectroscopy was used to study the reaction of ClOO with NO in 50-150 Torr total pressure of O2/N2 diluent at 205-243 K. A value of k(ClOO+NO) = (4.5 +/- 0.9) x 10(-11) cm3 molecule(-1) s(-1) at 213 K was determined (quoted uncertainties are two standard deviations). The yield of NO(2) in the ClOO + NO reaction was 0.18 +/- 0.02 at 213 K and 0.15 +/- 0.02 at 223 K. An upper limit of k(ClOO+Cl2) < 3.5 x 10(-14) cm3 molecule(-1) s(-1) was established at 213 K. Results are discussed with respect to the atmospheric chemistry of ClOO and other peroxy radicals.     

Responses of Bruguiera gymnorrhiza to saltwater monitored by miniature electrodes

We measured the voltage between two Ag/AgCl electrodes, one inserted into the seedling of the salt-tolerant plant Bruguiera gymnorrhiza and the other into the vermiculite in which the seedling was potted. Four seedlings were placed in different environments, in saltwater or pure water, with light or alternating light/dark conditions. We have found that (1) the voltage profiles showed periodical oscillatory behavior; (2) seedlings in saltwater showed higher voltage compared to the ones in pure water; (3) in the light environment, the voltage was higher compared to the one in the dark environment; (4) in the dark environment, a voltage wave was hardly observable; and (5) electrodes inserted into the propagule cortex, stem cortex, and petiole showed different voltage wave amplitudes. The voltage profiles will provide an effective way to evaluate the movement of salt water inside the salt-tolerant plant.     

Preserving life of moss Ptychomitrium under very high pressure

The experiment on the search for life under very high pressure done on small animal, tardigrade, has been extended to the moss Ptychomitrium. Several spore placentas of the moss Ptychomitrium were sealed in a small Teflon capsule together with fluorinate as liquid pressure medium. The capsule was put in the center of a pyrophillite cube. This cube was compressed by six tungsten-carbide second-stage anvils with a front edge length of 4.0 mm. These anvils were compressed by a first stage, 250 ton press. It was proven that 80-90% of the spores were alive and germinated after being exposed to the maximum pressure of 7.5 GPa for up to 48 h. Furthermore, a relatively high germination rate of about 35% was retained even after exposure to 7.5 GPa for 6 days. The pressure tolerance of moss is found to be much stronger than tardigrades.     

Time-of-flight imaging method to observe signatures of antiferromagnetically ordered states of fermionic atoms in an optical lattice

We propose a simple method to detect the antiferromagnetic (AF) state of fermionic atoms in an optical lattice by combining a time-of-flight (TOF) imaging method and a Feshbach resonance. In this scheme, the nontrivial dynamics of fermionic atoms during the imaging process works as a probe with respect to the breaking of the translational symmetry in the AF state. Precise numerical simulations demonstrate that the characteristic oscillatory dynamics induced by the scattering process that transfers an AF ordering vector appears in TOF images, which can be easily observed experimentally.     

Positron annihilation lifetime study of continuous volume phase transition of poly(N-isopropylacrylamide) gel induced in methanol–water mixed solvent

The macroscopic volume shrinkage and swelling of poly(N-isopropylacryl-amide) (PNIPA) gel induced by the compositional change in the methanol–water mixed solvent is correlated to the change in the nanoscopic free volume size and numerical concentration formed in the PNIPA gels. The free volume size and numerical concentration are estimated from the longest component appearing in the positron annihilation lifetime curves. The apparent free volume fraction calculated by the free volume size and numerical concentration, and dispersion of the free volume deduced by the size distribution are utilized to analyze the origin and location of the free volumes. The free volume parameters obtained by analysis of the positron annihilation data show various nanoscopic phases occuring within the PNIPA gels during the volume change, implying the variation of the strength of the interactions among the solvent molecules and the polymer chains of the PNIPA. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1141–1151, 1998     

Two‐Phase System Utilizing Hydrophobic Metal–Organic Frameworks (MOFs) for Photocatalytic Synthesis of Hydrogen Peroxide

Much effort has been devoted to photocatalytic production of hydrogen peroxide (H₂O₂) as an alternative to fossil fuels. From an economic point of view, reductive synthesis of H₂O₂ from O₂ coupled with the oxidative synthesis of value‐added products is particularly interesting. We herein report application of MIL‐125‐NH₂, a photoactive metal–organic framework (MOF), to a benzylalcohol/water two‐phase system that realized photocatalytic production and spontaneous separation of H₂O₂ and benzaldehyde. Hydrophobization of the MOF enabled its separation from the aqueous phase. This resulted in enhanced photocatalytic efficiency and enabled application of various aqueous solutions including extremely low pH solution which is favorable for H₂O₂ production but fatal to MOF structure. In addition, a highly concentrated H₂O₂ solution was obtained by simply reducing the volume of the aqueous phase.     

Alternating copolymerization of fluoroalkenes with carbon monoxide

The palladium-catalyzed alternating copolymerization of fluoroalkenes, represented as CH(2)=CH-CH(2)-C(n)F(2n+1), with CO was performed using (R,S)-BINAPHOS (2e) as a ligand. The CH(2)-C(n)F(2n+1) group is the most electronegative substituent ever reported for the copolymerization (Taft's sigma value of 0.90 for CH(2)CF(3)). The copolymer obtained from CH(2)=CH-CH(2)-C(8)F(17) (1a) existed as a mixture of polyspiroketal and polyketone, while that from CH(2)=CH-CH(2)-C(4)F(9) (1b) was a pure polyspiroketal, as was revealed by infrared and (13)C-CP/MAS NMR spectroscopies. The terminal structure of the polymer from 1b was confirmed by MALDI-TOF MS spectrometry. Detailed NMR studies suggested that the much higher reactivity with (R,S)-BINAPHOS (2e) than that with the conventional ligand DPPP (2a) can be attributed to the unique 1,2-insertion of the fluoroalkene into acylpalladium species. The existence of an electronegative substituent on the alpha-carbon of the palladium center is successfully avoided in the 1,2-insertion mechanism.     

Reduction of Pt usage in fuel cell electrocatalysts with carbon nanotube electrodes

The 12 wt% Pt-deposited carbon nanotube electrode gives 10% higher voltages than 29 wt% Pt-deposited carbon black and reduces the Pt usage by 60% in polymer electrolyte fuel cells with hydrogen and oxygen.