Showing papers on "Infrared spectroscopy published in 1987"

Sum-frequency vibrational spectroscopy of a Langmuir film: Study of molecular orientation of a two-dimensional system.

Abstract: Using infrared-visible sum-frequency generation as a probe, we have obtained the vibrational spectrum of a monolayer of pentadecanoic acid on a water surface in the CH stretch region. We have monitored the molecular orientation at different surface densities. It was found that the molecules in the liquid condensed phase have their alkane chains extended and oriented nearly normal to the surface, while in the liquid expanded phase the chains are highly disordered.

Surface vibrational spectroscopy by infrared-visible sum frequency generation

Abstract: We report the first observation of a vibrational spectrum of a monolayer of molecular adsorbates by infrared-visible sum frequency generation. The results pave the way for future dynamic studies of surface phonons and molecular vibrations.

Low‐temperature growth of silicon dioxide films: A study of chemical bonding by ellipsometry and infrared spectroscopy

Abstract: This paper presents a spectroscopic study using the techniques of ellipsometry and infrared (IR) absorption spectroscopy of the chemical bonding in silicon dioxide (SiO2) films grown in dry oxygen ambients at temperatures between 550 and 1000 °C. We find that the index of refraction at 632.8 nm increases and the frequency of the dominant IR active bond‐stretching vibration at about 1075 cm−1 decreases as the growth temperature is decreased below 1000 °C. Comparing the properties of these films with suboxides (SiOx, x<2) grown by plasma‐enhanced chemical vapor deposition, and compacted bulk silica has lead us to conclude: (i) that films grown at temperatures at or below 1000 °C are homogeneous stoichiometric oxides (SiO2); and (ii) that the systematic and correlated variations in the index of refraction and the IR frequency result from increases in the film density with decreasing growth temperature. We present a microscopic model that accounts for (i) the increases in the density and the index of refracti...

Strong 8.2 μm infrared intersubband absorption in doped GaAs/AlAs quantum well waveguides

Abstract: We have measured the infrared intersubband absorption at 8.2 μm in doped GaAs/AlAs quantum well superlattices. Waveguide geometry experiments demonstrate strong absorption with 95% of the incident infrared energy being absorbed.

Structure and Dynamics of Weakly Bound Molecular Complexes

Abstract: I. Spectroscopy, Structure, Potentials.- A. Rotational Spectra.- Rotational Spectroscopy of Weakly Bound Complexes: Capabilities and Limitations.- Pulsed-Nozzle, Fourier-Transform Microwave Spectroscopy of Hydrogen-Bonded Dimers.- Structure Determination of Weakly Bound Complexes.- Microwave Spectra and Weak Intramolecular Hydrogen Bonding in 3-Butene-1-Thiol and N-Methylallylamine.- B. Rotation-Vibrational Spectra.- High Resolution Infrared Spectroscopy of van der Waals Molecules.- Vibration-Rotation Spectroscopy of ArHCl by Far-Infrared Laser and Microwave/Far-Infrared Laser Double Resonance Spectroscopy.- Vibrational Anomalies and Dynamic Coupling in Hydrogen-Bonded van der Waals Molecules.- Slit Jet IR Absorption Spectroscopy of Molecular Complexes.- Sub-Doppler Resolution Infrared Spectroscopy of Binary Molecular Complexes.- The Infrared Spectrum of H2-Ar: New Observations in the v=l-0 and 2-0 Bands of H2.- Dynamical Properties of Simple Hydrogen-Bonded Clusters.- Infrared Spectroscopy of Hydrogen-Bonded and van der Waals Complexes.- Ab Initio Calculations of Vibrational Frequencies and Infrared Intensities for the Hydrogen- Bonded Complex HCN-HF.- The Role of Tunneling Models in Analyzing High- Resolution Spectra of Weakly Bound Molecular Complexes.- Bibliography of Rotational Spectra of Weakly Bound Complexes.- C. Electronic Spectra.- Structure and Dynamics of Mercury van der Waals Complexes.- The Structure of van der Waals Molecules of s-Tetrazine.- Spectra of Mixed Dimers.- Solvent Shifts, Spectroscopy and Structure in van der Waals Complexes of Perylene.- Spectroscopy in the Visible and Near Ultraviolet Region of Some Organic Molecules and their van der Waals Complexes.- Supersonic Jet Spectroscopy of Complexes of Carbazole and N-Ethyl Carbazole with Alkyl Cyanides.- Photoionization of Hydrogen-Bonded Molecular Aggregates.- D. Potential Functions.- The Unavoidable Importance of Electrostatic Effects in the Structures of Weakly Bonded Complexes.- Intermolecular Potentials, Internal Motions and the Spectra of van der Waals Molecules.- Non-Bonding Atom-Diatom Potentials via a Double Many-Body Expansion Method.- The Determination of Intermolecular Forces by Data Inversion Methods.- Transport Properties of van der Waals Molecules Computed from Accurate Interactions.- Determination of Anisotropic Interaction Potentials from Rotational State Resolved Scattering Data.- van der Waals Interactions from Glory and Diffraction Scattering.- High Resolution Crossed Molecular Beam Studies of van der Waals Forces.- E. Summary: Part.- Where Are We in Weak Intermolecular Interactions?.- II. Dynamics.- Interpretation of Linewidths in the Infrared Photodissociation Spectra of van der Waals Molecules.- Infrared Photodissociation of van der Waals Complexes Selectively Prepared by Molecular Beam Scattering.- IR Dissociation of Weakly Bound van der Waals Complexes: (SF6)n, (SiF4)n, (SiH4)n, (C2H4)n,(n=2,3) in the 9-11 in ?m Range.- Infrared (9-11?m) Dissociation of the Hydrogen Bonded Clusters (NH3)n (n?2)Detected by Bolometric Technique.- Highly Excited Systems.- Vibrational Predissociation Dynamics of the Nitric Oxide Dimer.- Complex Forming Reactions in Noble Gas Clusters.- Structure and Dynamics of the Rare Gas-Halogen van der Waals Molecules: Product State Distributions for Vibrational Predissociation of NeBr2.- Dynamics of Energy Transfer in van der Waals Molecules of s-Tetrazine and Argon.- Theory of van der Waals Photofragmentation Dynamics.- Dissociation Dynamics of the He-I2-Ne van der Waals Complex.- Dynamics of the Ar---H2 van der Waals Complex: A Diabatic Distorted Wave Approach Including Discrete-Discrete Couplings.- Vibrational Predissociation Dynamics of Weakly Bonded Dimers: A Summary.- List of Participants.- List of Contributors.- List of Poster Papers.- List of Names.

Infrared and x-ray photoelectron spectroscopy study of carbon monoxide and carbon dioxide on platinum/ceria

Abstract: The adsorptions of CO and CO/sub 2/ on Pt/CeO/sub 2/ were studied by infrared and X-ray photoelectron spectroscopy. A heterogeneous distribution of linearly adsorbed CO on Pt at terrace, step, and corner sites was proposed based on changes in the absorption of the CO infrared stretching frequencies from 2084 to 2060 cm/sup -1/ upon heating under vacuum from 300 to 473 K. Pretreatment of the sample with O/sub 2/ above 373 K lead to a blue-shifted peak at 2091 cm/sup -1/, interpreted as arising from CO adsorbed on Pt with an atom of oxygen at a neighboring site, and a new peak at 2131 cm/sup -1/, assigned to CO coadsorbed with an oxygen atom on the same Pt atom. Adsorption of CO/sub 2/ at room temperature resulted in the appearance of an IR band at 2065 cm/sup -1/, assigned to CO adsorbed on a Pt atom on a step or corner. The intensity of the CO band from CO/sub 2/ adsorption was sensitive to pretreatment of the sample, being completely suppressed by preoxidation but enhanced by prereduction. Lattice oxygen vacancies in the support, CeO/sub 2/, in the vicinity of the Pt particles are responsible for the formation of CO frommore » CO/sub 2/. XPS spectra show that Ce/sup 3 +/ is formed by the prereduction treatment, supporting the proposal that lattice oxygen vacancies play an important role in the CO/sub 2/ decomposition. Preoxidation is shown to lead to the formation of Pt/sup 2 +/ XPS (4f) spectra, which is removed by flash heating. Disproportionation of CO to carbon and CO/sub 2/ was shown not to occur by pretreatment of the surface with CO at 573 K.« less

Transformation of Birnessite to Buserite, Todorokite, and Manganite under Mild Hydrothermal Treatment

Abstract: Investigations were conducted to determine the hydrothermal transformations of synthetic birnessite exchanged with different metal ions. Autoclaving in a Teflon-lined stainless steel pressure vessel at 155°C for 24 hr of Mg-, Ca-, La-, and Co-saturated birnessite yielded manganese minerals having 10-A X-ray powder diffraction (XRD) spacings. The autoclaved Mg-birnessite yielded a mineral identical to natural todorokite in its infrared (IR) spectrum and XRD patterns. High-resolution transmission electron microscopy (HRTEM) provided images having 10-, 12.5-, 15-, and 20-A wide fringes indicating heterogeneous channel widths in the crystallographic a direction, and IR spectroscopy produced bands at 757, 635, 552, 515, 460, and 435 cm’1, confirming the product obtained by autoclaving Mg-birnessite to be todorokite. Prolonged autoclaving of Mg-birnessite yielded manganite (λ-MnOOH) as a by-product; manganite did not form when the autoclaving time was shortened to 8 hr. Also, when Ca-saturated samples were autoclaved, the product gave d-values of 10 A, but the XRD lines were broad and heterogeneity of the channel sizes was evident from HRTEM observations. The Ca-derivative had an IR spectrum similar to that of natural todorokite. Images showing 10-A lattice fringes were observed by HRTEM for the Ni-saturated sample, which also produced an XRD pattern similar to that of the Mg-saturated sample. Co- and Lasaturated samples did not form todorokite, although HRTEM of La-saturated samples indicated some 10-A lattice fringes that were unstable in the electron beam. Birnessite saturated with Na, K, NH4, Cs, Ba, or Mn(II) gave products having 7-A spacings upon autoclaving.

Optical constants of minerals and other materials from the millimeter to the ultraviolet

Abstract: : Reflectance spectra of near normal incidence and/or transmittance spectra of 29 materials were acquired in the ultraviolet, visible, and infrared spectra regions. Optical constants of the materials were determined primarily by use of Kramers-Kronig analysis of reflectance or extinction coefficient spectra. The materials were: Sodium chloride, Potassium chloride, Cesium iodide, Cesium bromide, Zinc sulfide, Zinc selenide, Barium fluoride, Zinc, Manganese, Molybdenum, Zirconium, Anhydrite, Dolomite, Montomorillonite, Kaolin, Illite, Composite of clays, Lanthanum hexaboride, Diesel soot, Polydimethylsiloxane, Dimethyl methylphosphonate, Diethyl sulfite, Diisopropyl methyl phosphonate, and Diethylphthalate.

The Disks of T Tauri Stars with Flat Infrared Spectra

Abstract: The energy distributions of T Tauri stars with flat infrared spectra is modeled by assuming that they have spatially thin disks with unorthodox radial gradients of temperature. Derived model parameters show that the disks associated with the flat-spectrum sources must contain intrinsic luminosity in addition to the energy intercepted and reprocessed from the central star, i.e., the disks must be active. Self-gravity may provide a possible source for this activity.

The structure of the carbon dioxide dimer from near infrared spectroscopy

Abstract: An F‐center laser–molecular beam spectrometer has been used to obtain a sub‐Doppler resolution infrared spectrum of the carbon dioxide dimer. The vibrational mode investigated in this study corresponds to the ν1+ν3 combination mode of the monomer located at 3716 cm−1. A qualitative assignment of the spectrum shows unambiguously that the equilibrium structure of the dimer is the slipped parallel, rather than the T‐shaped, geometry. The observed spectrum cannot be fit to within experimental error using conventional asymmetric rotor formalism. This may be due to a number of factors such as Fermi resonance between the upper state levels of the band and nearby levels of the dimer, such as seen in the monomer, or it could arise from tunneling effects arising from the two large amplitude motions in the dimer.

Infrared studies of fully hydrated unsaturated phosphatidylserine bilayers. Effect of Li+ and Ca2+.

Abstract: The thermotropic phase behavior of fully hydrated Na+ and/or NH4+ salts of 1,2-dimyristoyl-sn-glycero-3-phospho-L-serine (DMPS) was determined by temperature-dependent infrared spectra. The molecular level properties and thermal phase behavior of DMPS-Li+ complexes were also characterized by infrared spectroscopy. With increasing concentrations of Li+, the infrared spectra reveal the appearance of a second, more ordered, lipid phase which shows a gel to liquid-crystal transition at significantly higher temperatures (75-95 degrees C) than the Na+ or NH4+ salts of DMPS (39 degrees C). Li+ binds to the phosphate and carboxylate groups of DMPS, resulting in the following changes: (1) water of hydration is lost from both the carboxylate and phosphate groups; (2) there are changes in the conformation of the glycerol backbone but not in the P-O ester bonds of the phosphate group which remain in the gauche-gauche conformation; and (3) the packing of the fatty acyl chains becomes more ordered. In addition, the properties of the DMPS-Ca2+ complex were studied by infrared spectroscopy. While the DMPS-Ca2+ complex is also characterized by rigidly packed, well-ordered fatty acyl chains, the mode of Ca2+ binding to the DMPS head groups differs significantly from that of Li+ binding. By comparison, with dry DMPS-Ca2+ [Casal, H. L., Mantsch, H. H., Paltauf, F., & Hauser, H. (1987) Biochim. Biophys. Acta (in press)], the phosphate group undergoes a conformational change, probably to the antiplanar-antiplanar conformation, and loses its water of hydration.(ABSTRACT TRUNCATED AT 250 WORDS)

Preparation and characterization of bidimensional zeolitic structures obtained from synthetic beidellite and hydroxy-aluminum solutions

Abstract: Beidellite was synthesized hydrothermally from a noncrystalline gel at 320~ and 130 bar pressure. The beidellitic character of the product was verified by infrared spectroscopy on the NH4 § exchanged form. Intercalation was achieved with hydroxy-aluminum solutions having different OH/A1 molar ratios. The solutions were investigated by several methods, including 27A1 nuclear magnetic res- onance. Essentially, two Al species were detected: monomeric A1 and a polymerized form containing A1 in four-fold coordination. This latter species was found to be selectively fixed in the interlamellar region, which resulted in a stable spacing of 18 ,~ at 110~ and 16.2 ~ at 700~ The pillared beidellites had specific surface areas of > 300 m2/g, mainly due to micropores. Both Br6nsted and Lewis acid sites were evidenced by infrared spectroscopy using pyridine as a probe molecule.

Synthetic, electrochemical, optical, and conductivity studies of coordination polymers of iron, ruthenium, and osmium octaethylporphyrin

Abstract: A series of ligand-bridged metalloporphyrin polymers, (M(OEP)(L-L))/sub n/ (M = Fe, Ru, Os; L-L = pyrazine, 4,4'-bipyridine, 1,4-diazabicyclo(2.2.2)octane), have been synthesized and characterized. When partially oxidized, these polymers are highly conductive. The conductivity of these polymers depends on the extent of doping, the nature of the central transition metal, and the bridging ligand. The doped polymers exhibit strong infrared absorptions due to mixed-valence transitions, the features of which correlate with the bulk conductivity. The infrared spectra of the doped (Os(OEP)(pyz))/sub n/ samples reveal the presence of a coupling between an IR-silent vibrational mode of the bridging ligand and a mixed-valence transition, which suggests that the bridging ligand participates in the conduction process. Electrochemical studies of the polymers have been carried out with carbon cloth electrodes. These studies demonstrate that the doping reactions are metal-centered and corroborate the assertion that the porphyrin ..pi..-electrons are not involved in the conduction pathway. This feature contrasts with most of the previous work with porphyrinic conductors in which the conduction pathway is dominated by the macrocycle.

The à 2Π–X̃ 2Σ+ transition of HC2 isolated in solid argon

Abstract: Fourier transform absorption spectra have been obtained between 700 and 7900 cm−1 at a resolution of 0.2 cm−1 for Ar:C2H2 samples codeposited at 12 K with a beam of argon atoms that had been excited in a microwave discharge. Detailed isotopic substitution studies have confirmed that the predominant product species is HC2, which contributes not only the absorptions previously assigned to its two stretching fundamentals but also several weaker absorptions in the 2000–3600 cm−1 spectral region and a prominent, complicated pattern of absorptions between 3600 and 7800 cm−1. The previous assignment of the 3611 cm−1 HC2 absorption as the CH‐stretching fundamental is reviewed, and the assignment of an absorption at 2104 cm−1 as ν2+ν3 of ground‐state HC2 is discussed. The near infrared absorption band system has been assigned to the A 2Π–X 2Σ+ transition of HC2, extensively perturbed by interaction with high vibrational levels of the ground state. The position of the transition origin could not be definitively e...

Structure and vibrational spectroscopy of the water dimer using quantum simulation

Abstract: A method is described for calculating the vibrational frequencies of a molecular cluster using a combination of quantum simulation and local-mode variational theory. The method is applied to the water dimer and results are compared with normal-mode theory, frozen field local-mode theory, and with experiment. It is shown that the new approach is more rapidly convergent than the other techniques. Also, providing a suitable potential surface is available, the method is readily applicable to other molecular clusters.