Magnetic and infrared study of CO chemisorption on silica supported nickel-copper alloys

CO adsorption at room temperature on Ni-Cu alloys supported on SiO₂ is studied by two complementary techniques, infra-red spectroscopy and magnetic methods (saturation magnetization). The bond number between CO and the metallic surface calculated from magnetic data decreases from 1.8 to 1 as the Cu content increases. Two bands attributed to CO bonded to Ni are observed (the A band in the 2000–2050 cm^?1 region, and the B band in the 1950–1900 cm^?1 region). A small band assigned to CO bonded to Cu is also detected. As Cu content increases, the intensity of the B band decreases, and a noticeable and continuous frequency shift of the three bands is observed. Experimental results are fully accounted for assuming that: (i) two adsorbed species of CO on Ni, a monodentate and a bridged species (with small amounts of other multicentered species) are formed, as suggested by Eischens and Pliskin; (ii) dilution of Ni by Cu decreases the relative abundance of the bridged (and multicentered) species for some geometric reasons previously invoked by Soma-Noto and Sachtler; (iii) surface complexes are formed between CO and Ni; however Ni remains in its metallic state. The surface complex is sensitive to the electronic environment of the metallic atom, with a frequency shift of the three infra-red bands upon alloying as a consequence.     

Hydrogen-bonded OH and OD overtone bands and potential energy curve of methanol

The absorption spectra of CH₃OH, CH₃OD, CD₃OH, and CD₃OD as pure liquids and as carbon tetrachloride solutions were measured in the 3,850 – 16,600cm^?1 region. In addition to the various combination bands, the higher overtone bands of the hydrogen-bonded OH stretching vibration of self-associated methanols were observed at ～6470, 9300–9700, and 12,200 – 12,700 cm^?1 with broad half-widths of ～700, ～1200, and ～1800 cm^?1, respectively, and those of the OD stretching vibration, at ～4900, 7200–7400, and 9200–9600 cm^?1 with half-widths of ～370, ～700, and ～1200 cm^?1, respectively. With the aid of the observed frequencies, we determined the single minimum potential energy curve for the hydrogen-bonded OH and OD stretching vibrations of self-associated methanols. Furthermore, the absorption band due to double excitation of two neighboring OH groups linked together by a hydrogen bond was quantitatively analyzed by using the isotopic isolation technique. The double excitation band of CH₃OH as pure liquid was found to appear at 6730 cm^?1 with an absorbance of 0.08 at 1 mm light path length.     

Pure Rotational Raman Spectra of Vapor Phase Methanols

Abstract

The rotational Raman spectra of four vapor phase isotopic methanols, CH₃OH, CH₃OD, CD₃OH and CD₃OD, have been reported for the first time in the wavenumber regions from 5 to 100–120 cm^?1. The major parts of the spectra consist of bands equispaced at 3.19, 3.04, 2.56 and 2.46 cm^?1 intervals, respectively, and have been interpreted as the pure rotational S-branch transitions.     

Fourier transform infrared spectrum of thioketene,CH2CS

The FTIR spectrum of the unstable species thioketene, CH₂CS, has been detected in a vapor-phase flow pyrolysis system. The region 800–3500 cm^?1 has been surveyed with a resolution of 1 cm^?1, enabling the frequencies of the six fundamentals which lie above 800 cm^?1 to be determined. Certain bands have been studied under very high resolution and the results of the analyses of the perpendicular bands ν₇ and ν₃ + ν₈, observed with a resolution of 0.01 and 0.005 cm^?1 respectively, are presented. The ground state constant, A₀, is determined as 286 453.60(58) cm^?1.     

Characterization of the adsorption and decomposition of methanol on Ni(110)

The chemisorption, condensation, desorption, and decomposition of methanol, both CH₃OH and CH₃OD, on a clean Ni(110) surface have been characterized using high resolution electron energy loss spectroscopy, temperature programmed reaction spectroscopy, and low energy electron diffraction. The vibrational spectrum of the saturated chemisorbed layer, 7.4 × 10¹⁴ molecules cm^?2, is almost identical to the infrared spectrum of liquid or solid methanol. Condensation of multilayers of methanol is facile at 80 K. The only quasi-stable intermediate isolated during the decomposition is a methoxy species, CH₃O, which decomposes thermally to CO and H. The evolution of both CO and H₂ occurs in desorption limited processes.     

The absorption spectrum of 12C2H2 between 12800 and 18500cm−1 II. Rotational analysis

The rotational structure of the vibrational bands of ¹²C₂H₂ is investigated in three spectral energy regions not previously systematically explored at high resolution, 12800–13500 cm^?1, 14000–15200 cm^?1 and 16500–18360 cm^?1, on the basis of new spectral data recorded by intracavity laser absorption spectroscopy. The rotational analysis of 17 new absorption bands arising from the ground state is reported (11 Σ_u ⁺ ? Σ_g ⁺ bands and 6Π_u ? Σ_g ⁺ bands). Four bands in the range studied show strong perturbations affecting both the line positions and intensities. Their detailed analysis is performed in order to determine the nature of the coupling schemes, the vibrational species and the rotational constants of the perturber states. Altogether, the vibration-rotation parameters of 21 newly observed vibrational states are derived.     

3-Naphthyl-4-Quinazolone Infrared and Nuclear Magnetic Resonance Band Assignments

Abstract

The ir and nmr spectra of 24 3-naphthyl-4-quinazolones were examined. There are three principal ir bands in the 1500 and 1705 cm^?1 region of the spectra. The first at 1685–1705 cm^?1 is assigned to the tertiary amide carbonyl (ArCONR₂), the second at 1593–1645 cm^?1 to the anil chromophore (ArN=C-N) and the third to the naphthalene ring at 1600 cm^?1. The nmr band assignments are straight forward.     

Vibrational analysis of ethylamines: Trans and gauche forms

Starting from force constant values calculated by an ab initio MO method ($\text{4-31G(N}{}^1\text{)}$), and by adjusting the diagonal elements, a practical force constant matrix (F) has been reached which could explain the observed infrared and Raman spectra (in the frequency range lower than 2000 cm^?1) of the gauche form of the ethylamine CH₃CH₂NH₂ molecule and five isotopic species CH₃¹³CH₂NH₂, CH₃CH₂¹⁵NH₂, CH₃CD₂NH₂, CH₃CH₂ND₂, and CD₃CD₂NH₂. The F matrix for the trans form of ethylamine was constructed by transferring ab initio $\text{4-31G(N}{}^1\text{)}$ values and by revising diagonal elements with conversion factors whose values are equal to the corresponding values of gauche form. A nearly complete set of assignments was achieved of the vibrational bands of ethylamines, observed so far in the spectral range 2000–100 cm^?1. In matrix isolation spectroscopy, two bands assignable to the NH₂ wagging vibrations of gauche and trans forms have been found at 775 and 782 cm^?1, respectively, for CH₃CH₂NH₂. They are at 768 and 774 cm^?1, respectively, for CD₃CD₂NH₂. From the intensity changes of these bands observed on changing the nozzle temperature in the matrix formation, the energy difference ΔE (gauche-trans) of these two conformers has been estimated to be 100 ± 10 cm^?1.     

Infrared Spectra of the Square Planar Rhodium(I) Complexes cis-[Rh(CO)2(pyridine) (X)] (X = Cl,Br): Isotopic Labelling Studies and Normal Coordinate Analysis

Abstract

The infrared spectra (4000 - 50 cm^?1) of the square planar rhodium(I) complexes cis-[Rh(CO)₂ (pyridine) (X)] (X = Cl, Br) and their isotopomers with pyridine-d ₅ and ¹³CO have been determined. Assignments are based on earlier studies on pyridine and its complexes and on the shifts in infrared bands which are caused by the isotopic substitutions employed. Normal coordinate analysis following the procedure of Becher and Mattes has been used to confirm the empirical assignments. The two v(RhC) bands are observed near 490 and 450 cm^?1. v(RhN) is found near 210 cm^?1 and v(RhX) occurs at 310 (X = Cl) and 235 (X = Br) cm^?1. At frequencies below 200 cm^?1, the bands are assigned to bending modes in the following sequence: δ (RhN) > δ (CRhC) > δ (RhCl) > γ (RhCl) > γ (RhN).     

A radiotracer study of slow electron interaction with co on polycrystalline Mo

The interaction of slow (50–300 eV) electrons with CO chemisorbed on a polycrystalline Mo ribbon was investigated. A radiotracer was employed to monitor C concentration on the surface and desorbed ions were collected. From the time variation of the ion current, total electron induced desorption cross sections of 3.7 × 10^?17 to 1.6 × 10^?16 cm² were obtained. The desorption cross section for C containing species was found to be less than 1.4 × 10^?19 cm². In addition, the sticking coefficient for CO on Mo was found to be 0.13–0.16. These results are discussed in terms of the states of chemisorbed CO and the conclusions of other investigations of this systems.     

Infrared Quantitative Study of Acetylation of Microspheres of Polystyrene

Abstract

Fourier transform infrared spectroscopy has been used to study quantitatively the acetylation of monodisperse polystyrene microspheres with diameters ranging from 7 to 9μm. The CH₂ stretching infrared vibration mode at 2921 cm^?1 was used as the internal intensity standard. The acetylation extent could be easily measured by comparing the relative intensities of the bands of acetyl group (1678, 1415, 1359 cm^?1) or the bands due to the para-substituted benzene ring to the band at 2921 cm^?1 from the calibration curve.     

The chemisorption of nitrogen on the (001) surface of ruthenium

High resolution electron energy loss spectroscopy (EELS), thermal desorption mass spectrometry (TDMS) and low energy electron diffraction (LEED) have been used to investigate the molecular chemisorption of N₂ on Ru(001) at 75 K and 95 K. Adsorption at 95 K produces a single chemisorbed state, and, at saturation, a (√3x√3) R30° LEED pattern is observed. Adsorption at 75 K produces an additional chemisorbed state of lower binding energy, and the probability of adsorption increases by a factor of two from its zero coverage value when the second chemisorbed state begins to populate. EEL spectra recorded for all coverages at 75 K show only two dipolar modes — ν(RuN₂) at 280–300 cm^?1 and ν(NN) at 2200–2250 cm^?1 — indicating adsorption at on-top sites with the axis of the molecular standing perpendicular to the surface. The intensities of these loss features increase and ν(NN) decreases with increasing surface coverage of both chemisorbed states.     

The adsorption of ammonia on a Fe(110) single crystal surface studied by high resolution electron energy loss spectroscopy (EELS)

EELS spectra of ammonia adsorbed on a Fe(110) single crystal surface at 120 K reveal four different molecular adsorption states:1. At very low exposures (0.05 L) three vibrational losses at 345 cm^?1, 1170 and 3310 cm^?1 are observed which are attributed to the symmetric Fe-N stretching-, N-H₃ deformation and N-H₃ stretching modes of chemisorbed molecular ammonia, respectively. The observation of only three vibrational losses indicates an adsorption complex of high symmetry (C_3v).2. Further exposures up to 0.5 L cause the appearance of additional losses at 1450 cm^?1, 1640 cm^?1 and 3370 cm^?1. The latter two are interpreted as the degenerate NH₃ deformation and - stretching modes of molecularly adsorbed NH₃. The 1450 cm^?1 loss is a combination of the losses at 345 cm^?1 and 1105 cm^?1. The observation of 5 vibrational losses is consistent with an adsorption complex of C_s symmetry.3. In the exposure range from 0.5 to 2 L adsorption of molecular ammonia in a second layer is observed. This phase is characterized by a symmetric deformation mode at 1190 cm^?1 and by two additional very intense modes at 160 cm^?1 and 350 cm^?1 which are due to rotational and translational modes.4. Exposures above 2 L cause multilayer condensation of ammonia characterized by translational and rotational bands at 190 cm^?1, 415 cm^?1 and 520 cm^?1, and a symmetric deformation mode at 1090 cm^?1. A broad loss feature around 3300 cm^?1 is attributed to hydrogen bonding in the condensed layer.Thermal processing of a Fe(110) surface ammonia covered at 120 K leads to decomposition of the ammonia into hydrogen and nitrogen above 260 K. No vibrational modes due to adsorbed NH or HN₂ species were detected.     

Unusual Bands in the Infrared Spectra of Some Chars

Abstract

When organic materials are charred at low or medium temperatures (up to about 450–500°C), their infrared (IR) spectra show a plethora of bands below about 2000 cm^?1, and there are additional bands in the OH and CH stretching regions, above about 2600 cm^?1. The in-between region, from about 2600 to 200 cm^?1, is quite “empty” (except for an occasional atmospheric CO₂ band caused by instrument imbalance). The reason for this emptiness is, simply, that there are very few species that have fundamentals in that region, as is well known from group frequency tables; and those that do absorb, such as metal hydrides, are quite unlikely to exist in organic precursors. Some overtones or combinations may appear, but these are usually very weak. We have, however, observed some bands in the empty region on several occasions.     

High resolution infrared synchrotron study of CH2D81Br: ground state constants and analysis of the ν5, ν6 and ν9 fundamentals

The high resolution infrared absorption spectrum of CH₂D⁸¹Br has been recorded by Fourier transform spectroscopy in the range 550–1075?cm^?1, with an unapodized resolution of 0.0025?cm^?1, employing a synchrotron radiation source. This spectral region is characterized by the ν₆ (593.872?cm^?1), ν₅ (768.710?cm^?1) and ν₉ (930.295?cm^?1) fundamental bands. The ground state constants up to sextic centrifugal distortion terms have been obtained for the first time by ground-state combination differences from the three bands and subsequently employed for the evaluation of the excited state parameters. Watson's A-reduced Hamiltonian in the I^r representation has been used in the calculations. The ν ₆?=?1 level is essentially free from perturbation whereas the ν ₅?=?1 and ν ₉?=?1 states are mutually interacting through a-type Coriolis coupling. Accurate spectroscopic parameters of the three excited vibrational states and a high-order coupling constant which takes into account the interaction between ν₅ and ν₉ have been determined.     

Structure comparison of Orpiment and Realgar by Raman spectroscopy

Raman spectroscopy was used to characterize and differentiate the two minerals, Orpiment and Realgar, and the bands related to the mineral structure. The Raman spectra of these two minerals are divided into three sections: (a) 100–250?cm^?1 region attributed to the sulfur–arsenic–sulfur bending vibrational modes; (b) 250–450?cm^?1 region due to the arsenic–sulfur stretching vibration; and (c) 450–850?cm^?1 region assigned to overtone and combination bands. A total of 14 Raman bands for the spectrum in the 1600–100?cm^?1 region were observed. The significant differences between the minerals Orpiment and Realgar are observed by Raman spectroscopy. Realgar shows the typical bands observed at 340, 268, 228, and 218?cm^?1, and the special bands at 379, 289, 200, 176, and 102?cm^?1 for Orpiment are observed. The additional bands in 850–450?cm^?1 region are only observed for the mineral Orpiment, which may be attributed to overtone and combination bands in the Raman spectrum. The variation in band positions is dependent upon the structural symmetry, arsenic–sulfur bond distances, and angles. Moreover, another cause for the difference is the effect of the intermolecular forces and to the strong coupling between close lying external and internal modes. The difference of these two minerals structure induce tremendous diversity on Raman spectra, so Raman spectroscopy offers the information on the molecular structure of the minerals Orpiment and Realgar.     

Quantum chemical studies of the OH-initiated oxidation reactions of propenols in the presence of O2

ABSTRACT

The atmospheric oxidation mechanisms of 1- and 2-propenol initiated by OH radical have been theoretically investigated at the CCSD(T)//BH&;HLYP/6-311?+?+G(d,p) level of theory. Conventional transition state theory was employed to predict the rate constants for the initial reaction channels. The calculations clearly indicate that OH-addition channels contribute maximum to the total reaction, both for 1- and 2-propenol, while H-abstraction channels can be neglected at the temperature range of 220–520?K. The calculated total rate constants at 298?K are 1.66?×?10^?11 and 7.69?×?10^?12 cm³?molecule^?1?s^?1 respectively for 1- and 2-propenol, which are in reasonable agreement with the experimental values of similar systems (vinyl ethers?+?OH reactions). The deduced Arrhenius expressions are k(OH?+?1-propenol)?=?1.43?×?10^?12 exp[(743.7?K)/T] and k(OH?+?2-propenol)?=?2.86?×?10^?12 exp[(310.5?K)/T] cm³?molecule^?1?s^?1. Under atmospheric condition, the OH-addition intermediates (CH₃C?HCH(OH)₂, CH₃CH(OH)C?H(OH), CH₃CH(OH)₂?CH₂, CH₃?C(OH)CH₂(OH)) are likely to react rapidly with O₂, the theoretically identified major products for 1-propenol are HCOOH, CH₃CHO and CH₃CH(OH)CHO, and the dominant products for 2-propenol are CH₃COOH, HCHO and CH₃COCH₂OH, both companied with the regeneration of OH and HO₂ radicals (crucial reactive radicals in the atmosphere).     

Magnon Raman scattering in the quasi 1-D antiferromagnet CsCoBr3

Raman scattering from magnons has been observed in the three magnetic phases of CsCoBr₃. In the 1-D Ising phase T > 28K a broad band at 96 cm^?1 is observed. This band grows in intensity but shows little renormalisation (100.5 cm^?1 at 14K) in the partially disordered antiferromagnetic phase 14K < T < 28K. For T < 14K additional structure at 111.5, 123.5, 133, and 141 cm^?1 is attributed to magnon-magnon combination bands. Two extra magnon branches are expected for this ferrimagnetic phase. One of these has an energy of ≈ 11 cm^?1.     

High resolution FTIR study of the ν5 and ν6 bands of CH2D35Cl: analysis of resonances and determination of ground and upper state constants

The isotopically pure form of methyl chloride, CH₂D³⁵Cl, was synthesized and investigated by Fourier transform infrared spectroscopy with an unapodized resolution of 0.004?cm^?1 in the range 650–900?cm^?1, the region of the lowest fundamentals ν₅ (827?cm^?1) and ν₆ (714?cm^?1). These distinct bands have been analysed in detail in the P-, Q- and R-branches. In spite of their expected a/b-hybrid nature, both envelopes show the peculiar characteristic of only a-type bands of near prolate asymmetric top molecules. Ground state parameters have been determined for the first time through ground state combination differences from both bands. Parameters of the excited vibrational states and coupling constants have been obtained using a model which accounts for c-type Coriolis interaction and ΔK_a?=?±?2 anharmonic resonance.     

Structure and rotational dynamics of methyl propionate studied by microwave spectroscopy

We report on the rotational spectra of the most abundant conformer of methyl propionate, CH₃CH₂COOCH₃, recorded with a Fourier transform microwave spectrometer under molecular beam conditions. We present accurate rotational constants and centrifugal distortion constants. For the propionyl CH₃ CH₂CO– methyl group and the methoxy –OCH₃ methyl group, barriers of 820.46(99)?cm^?1 and 429.324(23)?cm^?1, respectively, were found. For spectral analysis, two different computer programs were used, the code BELGI-C_s-2tops based on the rho axis method (RAM) and the code XIAM based on the combined axis method (CAM). The results are compared. The experimental work was supplemented by quantum chemical calculations. Potential energy functions for the rotation of the terminal methyl groups and also of the entire ethyl group were parametrized.