R. E. Hester

The dependence of the intensity of Raman bands of pyridine at a silver electrode on the wavelength of excitation

Abstract On increasing the wavelength of excitation over the range 350–700 nm, Raman bands of pyridine adsorbed at a roughened silver electrode are found to increase in intensity, relative to bands of the bulk medium (aqueous perchlorate or liquid pyridine) in contact with the electrode. The increase is observed in the bands at 1000–1050 cm −1 and 1600 cm −1 due to ring stretching, and similar increases are observed in other bands of the surface species, notably those due to CH stretching (3076 cm −1 ), b 2 ring deformation (669 cm −1 , and AgN stretching (239 cm −1 , which have not been reported previously.

Femtosecond time-resolved UV-visible absorption spectroscopy of trans-azobenzene: dependence on excitation wavelength

Femtosecond time-resolved UV-visible absorption spectroscopy has been used to study the photochemistry of trans-azobenzene in n-hexane. Excitation to the S-1(n pi*) state results in transient absorption bands at ca. 400 nm (strong) and 550 nm (weaker) which decay with a lifetime 2.5 +/- 0.2 ps on excitation at 503 nm, close to the S-1 origin, and with an additional fast component of ca. 0.6 ps on excitation at 390 or 420 nm, both well above the S-1 origin. Excitation to the S-2(pi pi*) state results in transient absorption at 400 nm which decays with a dominant component of ca. 0.9 ps and a weaker component of ca. 15 ps; this 400 nm band itself is observed to rise synchronously as a transient band at 475 nm decays with a lifetime of < 200 fs. These results are discussed in terms of the dual mechanism proposed for azobenzene photoisomerization.

Vibrational spectra and torsional barriers of anisole and some monohalogen derivatives

Abstract A vibrational analysis of the spectra of anisole and of the ortho, meta and para substituted fluoro, chloro and bromo derivatives has been carried out. The torsional barriers restricting rotation about the phenyl—O bond have been calculated from the torsional frequencies for the pure liquids. The barriers are consistently higher for meta derivatives than for para or ortho substituted compounds, with the exception of ortho chloro and ortho bromoanisoles. The existance of rotational isomers has been established for m-fluoro-anisole, the trans conformation being the more stable. The energy difference between the two rotamers in the liquid state was found to be 580 ± 150 cal mole .

Mining and its environmental impact

Mining Non-ferrous Metals The Environmental Impact of Gold Mining in the Brazilian Amazon Revegetation of Metalliferous Wastes and Land After Metal Mining Vegetative Remediation at Superfund Sites Green Coal Mining Methane Emissions from Coal Mining Constructing Ecosystems and Detecting their Connectivity to the Larger Ecological Landscape The Discharge of Waters from Active and Abandoned Mines Environmental Best-practice in Metals Production. Subject Index.

Resonance raman investigation of electronically excited ru(bipyridine)2+3 using a cw laser

Abstract Formulae are given to estimate the possibility of measuring resonance Raman (RR) spectra of an electronically excited species using cw lasers. The RR spectrum of Ru(bpy) 2+* 3 (τ = 600 ns) has been obtained using 65 mW at 350.6 nm. A vibrational analysis of Ru(bpy) 2+* 3 and comparison with the RR spectrum of free bpyXXX shows that Ru(bpy) 2+* 3 is essentially [Ru III (bpy) 2 bpyXXX] 2+ .

Photoisomerization of a Capped Azobenzene in Solution Probed by Ultrafast Time-Resolved Electronic Absorption Spectroscopy

Ultrafast time-resolved electronic absorption spectroscopy has been used to study the photochemistry of trans-azobenzene and trans-1, a derivative in which azobenzene is capped by an azacrown ether, on UV excitation to the S2(ππ*) state. Excitation of trans-1 results in transient absorption which decays with a dominant component of lifetime ca. 2.6 ps and in bleaching of the ground-state UV absorption band which recovers on a similar time scale. In contrast, excitation of trans-azobenzene results in transient absorption which decays with a dominant component with a shorter lifetime of ca. 1 ps, and in bleaching which recovers on a much longer time scale of ca. 18 ps. The recovery of the ground-state UV absorption band is not complete in either case, and the ultrafast data indicate that the quantum yield of trans-to-cis photoisomerization of 1 is approximately twice that of azobenzene. These observations demonstrate that the restricted rotational freedom of the phenyl groups in trans-1 has a significant ef...

Waste incineration and the environment

Incineration as a Waste Management Option Pollutants from Incineration: An Overview Recovering Energy from Waste: Emissions and Their Control Organic Micropollutant Emissions from Waste Incineration Pilot-scale Research on the Fate of Trace Metals in Incineration The US Approach to Incinerator Regulation Environmental Assessment and Incineration. Subject Index.

Biodiversity Under Threat

The biosphere is the layer of the earth where there is life and it includes parts of the atmosphere and lithosphere. Here there is an amazing variety of life forms, only some of which have been recorded by humans. The term biodiversity is a shortening of ‘biological diversity’. The 1992 Convention on Biological Diversity in Rio de Janeiro defined biodiversity as the “variability among living organisms from all sources... terrestrial, marine and aquatic ecosystems and the ecological complexes of which they are a part: this includes diversity within species, between species and of ecosystems”. Biodiversity is the sum of all three definitions: species, genetic and ecosystem diversity.

Environmental and health impact of solid waste management activities.

Overview of Waste Management Options: Their Efficacy and Acceptability Health Risks of Materials Recycling Facilities Microbial Emissions from Composting Sites Health Effects and Landfill Sites Emissions from Solid Waste Management Activities Health Impacts of Waste Incineration Methodological Issues Relating to Epidemiological Assessment of Health Risks of Waste Management Subject Index.

Atmospheric chemistry of PCBs, PCDDs and PCDFs

Polychlorinated biphenyls (PCBs), polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) (see Figure 1) are emitted into the atmosphere fromthe combustionof chlorine-containingmaterials.1—13Additionally, PCBs, which were used as lubricants and dielectric fluids,13 are volatilized into the atmosphere from soils and bodies of water (for example, from the Great Lakes) after their disposal or inadvertent release into, and cycling through, the environment.1,14—18 Atmospheric concentrations of PCBs, PCDDs and PCDFs have been measured at numerous locations,2,15,16,19—62 and these organochlorine