In certain applications, PSA systems filter contaminants only under transient conditions. This paper presents both experimental and modeling work for the transient, non-isothermal behavior of PSA for air purification. The solutes considered include the refrigerant vapors R-22, R-11 and water vapor and adsorbents activated carbon and 13X molecular sieve. Simultaneous concentration samples at four in-bed locations, product and purge are recorded. In-bed temperature profiles are reported for complete cycles. The in-bed profiles are shown to provide a detailed representation of the progress of the concentration wave for the transient behavior. The non-isothermal effects are examined for several conditions including inert packing, non-adsorbing carrier and a varying purge to feed ratios. Chemical contaminant filtration is presented for strongly and weakly adsorbed vapors. Good agreement is achieved between the model simulation and the measured PSA data.

Raman spectroscopy has been used to measure silicone and the organophosphorous compound dimethylmethylphosphonate (DMMP) with good sensitivity from the vapor above the liquid. This result confirms that atmospheric sampling using a low temperature collection method should allow part-per-million (ppm) or better sensitivity. Advanced methods are proposed which may sufficiently increase sensitivity enough to detect silicone at the sub-ppm level in air.

This paper examines a suite of lipid solvents for their utility as solvents for silicone analysis by Raman spectroscopy, and discusses the observation that off-the-shelf reagents could be contaminated by silicone during manufacture. Of the solvents examined, only chloroform was transparent in those spectral regions (chiefly 500 cm-1) in which silicone exhibits its Raman spectrum. Also, the chloroform examined showed evidence of silicone contamination. Therefore, chloroform is suggested as a suitable solvent for Raman spectroscopic work involving silicone, if one is careful to confirm that the chosen chloroform is not contaminated by silicone.

CO production in high-voltage alternating current (HVAC) silent discharge plasmas of air and air-methane mixtures at atmospheric pressure has been investigated by matrix isolation FTIR spectroscopy. In pure air, CO is produced by decomposition of CO2. A steady-state CO/CO2 ratio was determined by varying the flow rate. CO production was considerably enhanced when methane was added to the plasmas. CO production was observed even at very low oxygen concentrations, and did not noticeably decrease due to secondary oxidation reactions, even when methane was discharged in a pure oxygen carrier. CO production in air-methane mixtures is shown to depend on input power. CO production from CO2 and hydrocarbons in air appears to be a significant obstacle for development of a plasma-based air purification device.

The mechanism for activation of infrared absorption by N2 matrices has been studied. FTIR spectra of isotopically enriched CO2 trapped in N2 provide new and convincing evidence supporting the hypothesis proposed by Nelander that the activation is electromagnetic in origin for the CO2/N2 system. The N2 absorption appears to be triggered by the near coincidence of the N2 stretching frequency with the asymmetric stretch of C16O18O. The activation of absorption by N2 in matrices doped with H2O and C2N2 has also been observed. For these systems, however, alternate explanations for the activation appear to be necessary.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSurface-enhanced Raman spectroscopy of benzene adsorbed on vapor-deposited sodium. Chemical contribution to the enhancement mechanismPaul A. Lund, D. E. Tevault, and R. R. SmardzewskiCite this: J. Phys. Chem. 1984, 88, 9, 1731–1735Publication Date (Print):April 1, 1984Publication History Published online1 May 2002Published inissue 1 April 1984https://pubs.acs.org/doi/10.1021/j150653a014https://doi.org/10.1021/j150653a014research-articleACS PublicationsRequest reuse permissionsArticle Views279Altmetric-Citations29LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access options Get e-Alerts

Surface-enhanced Raman spectra (SERS) of pyridine adsorbed on copper, silver, and gold films vapor deposited on low temperature substrates are reported. Similar spectra were also obtained on a sputter-cleaned silver single crystal. Excitation spectra (450–750 nm) for all three metals revealed an overall increase in SERS activity at longer wavelengths, the relative increase being greater for copper and gold than silver. A broad excitation maximum near 2 eV was observed for the 1006 cm−1 pyridine SERS signal on silver. A lesser-defined maximum was revealed for copper in the same general vicinity (1.7–2.0 eV) while a broad onset extending below 1.7 eV was observed for gold. Temperature studies (15–300 K) indicate that the observed SERS originate from molecular pyridine chemisorbed to the metal surfaces. In the cases of copper and gold, SERS were also observed from samples maintained at room temperature in vacuum. The intensities of the SERS signals were proportional to incident (cw) laser power at low power densities (<1 MW/cm2).

The mechanisms of gas-solid reactions occurring on various carbons or carbon-supported metal catalysts have been examined by Fourier Transform Infrared (FTIR) spectroscopic techniques. In one series of experiments, reactant-air mixtures were passed through a temperature-ramped carbon bed. Desorption and/or combustion products were characterized and quantified downstream by real-time analysis of the effluent vapors in a rapid scanning FTIR spectrometer. Lower concentration components were collected via condensation on to a cryogenic IR-transmitting crystal and subsequently analyzed by FTIR methods.

Enhanced Raman spectra have been observed from small amounts of benzene and benzene-d6 adsorbed on vapor-deposited sodium surfaces held at 15 K. Many lines were observed which can be assigned to normally Raman-active benzene fundamentals as well as some that are normally forbidden in D6h symmetry.

The reactions of trifluoroacetic anhydride with palladium, nickel, and copper atoms at low temperatures have been studied by spectroscopic and synthetic techniques. Results indicate that metal-anhydride complexes are formed at low temperatures and subsequently decompose to give metal trifluoroacetates upon warming to ambient. The order of stability of these complexes is believed to be Ni < Cu < Pd. The reaction of Ni(CO)4 with trifluoroacetic anhydride also yields bis(trifluoroacetate) nickel.

AbstractAnregung von Ar‐ Matrices, die Cu‐Atome sowie 02‐ oder O3‐Moleküle enthalten, bei 10 Kmit den blauen Laser‐Linien eines Kr‐Lasers, bewirkt die Emission einiger Elektronenemissionen mit ausgedehnten Schwingungsstrukturen, die mit Hilfe von 13O‐Anreicherungsexperimenten als Emissionen des CuOz charakterisiert werden.

AbstractDie durch IR‐ spektroskopische Untersuchung der Argon‐Matrix‐Iso1ation und Metallatom‐Reaktot‐Versuche erhaltenen kombinierten Ergebnisse zeigen, daß die Reaktion von Tri‐ fluor‐acetanhydrid mit Pd‐, Ni‐ und Cu‐Atomen bei niedrigen Temp. zu Metall‐Anhydridkomplexen (I) führt, die sich beim Erwärmen auf Raumtemp. unter Bildung der Trifluoracetate (II) zersetzen.

Matrix isolated infrared spectra of AgO2 in Ar matrices is presented and a normal coordinate analysis of AgO2 is performed. (AIP)

Argon matrix reactions between Ag atoms or very small Ag clusters and pyridine molecules have been observed by infrared absorption spectroscopy. Pyridine-d5 experiments indicate that the reaction product contains a pyridine molecule whose vibrations are slightly altered by the metal atom. Analogous Cu atom matrix reactions with pyridine produced larger frequency shifts than the Ag atom reactions. Increased silver atom concentrations produced additional new absorptions which are attributed to the reaction products of very small Ag clusters with pyridine. These latter frequencies approached those of pyridine on rough metal surfaces observed in surface enhanced Raman spectroscopy (SERS). The vibrational similarities between the matrix infrared spectra of the Ag–pyridine and Agx–pyridine molecules and the SERS spectra of pyridine on various metal surfaces are discussed.

When argon matrices containing atomic Cu and O2 or O3 molecules at 10 K are excited with the blue laser lines of a krypton ion laser, several electronic emissions with extensive vibrational structure are observed. These were characterized as CuO2 emissions by the use of oxygen-18 isotopic enrichment experiments where each member is split into a triplet, thereby indicating a CuO2 molecule with equivalent oxygen atoms. A second progression observed only when Cu atoms were deposited with argon–ozone samples is tentatively attributed to a resonance Raman progression of the Cu2O molecule. No emissions from CuO have been observed in these experiments.

Ground state oxygen atoms, generated by visible photolysis of ozone, have been reacted with CH3SCH3 and CH3SH in argon matrices. For CH3SCH3, a stepwise addition to form DMSO and dimethylsulfone was observed. Methanethiol reactions with O atoms were more complex, leading to production of CH3SOH, CH3OSH, CH3S(O)H, and possibly CH3–SO2–H. These results are compared to the O+H2S reaction. The matrix results are also compared to gas phase studies where more extensive fragmentation has been observed, and inferences are drawn concerning the relative matrix deactivation rates of the highly energetic sulfide–oxygen-atom precursor complex.

Photooxidation of benzene at 254 nm has been studied in 10-KAr matrices. Both CO and CO2, which are believed to be secondary photodissociation products of initial peroxy-adducts or their dialdehyde isomers from the reaction of the triplet benzene with O2, were found to be the major observable oxidation products by IR analysis. Formation of these products has been studied as a function of photolysis time and of O2 concentration. On the basis of this result and estimates of transition state calculations, it can be concluded that at 2500K, the C6H6(T1) + O2 reaction is at least as important as the hydrogen abstraction reaction, C6H6 + O2 å C6H5 + HO2, for chain-initiation. The T1-state reaction is expected to be more important as its energy decreases for the larger members of the homologous series.