The adsorption of CO on Cu(110)

The adsorption of CO on Cu(110) has been studied by LEED, surface potentials and infrared spectroscopy. With increasing surface coverage the s.p. passes through a maximum value of 0.29 V and than falls to 0.17 V at saturation. The heat of adsorption is nearly constant (~55 kJ mol^?1) up to the maximum s.p. but then falls rapidly. A ( 2× 1) structure is formed near the s.p. maximum, followed by a structure which is compressed in the [11?0] direction and poorly ordered in the [001] direction but tending towards c(1.3 × 2). At low coverage two infrared bands appear at 2088 and 2104 cm^?1; their relative intensity is similar at 77, 195 and 295 K. As the coverage increases, the bands shift in frequency and merge into a single band at 2094 cm^?1. The origin of the two bands is discussed in relation to the overlayer structure. Strong interaction between CO molecules is shown by the spectra of mixtures of ¹³CO and ¹²CO.     

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.     

Coupled harmonic oscillator models of carbon monoxide adsorbed on stepped,platinum surfaces

Harmonic oscillator models are used to explain recent experimental data on infrared absorption by CO molecules adsorbed on two stepped platinum surfaces. These data reveal only a lower frequency band at low coverage and only a higher frequency band at high coverage. Both bands exist over a range of intermediate coverages. The data are explained by a coupled-dipole model which includes the effects of electronic polarizability, the tilted orientation of CO molecules at step sites, and the electric field enhancement at step sites. The lower-frequency band is associated with CO molecules adsorbed on step sites and the higher-frequency band is associated with two-dimensional islands consisting of both step and terrace CO. The model explains the observed variation of frequency and intensity with coverage for CO adsorption on Pt(533) and Pt(432) surfaces. The model calculations indicate that the wavenumber for a single, linearly bonded CO molecule is about 9 cm⁻¹ higher on a terrace site than on a step site.     

The interaction of CO and O2 with the (111) surface of Pt3Ti

The electronic properties of clean and partly oxidized Pt₃Ti(111) surfaces have been studied utilizing carbon monoxide both as a probe and as a reducing agent. Vibrational frequencies and desorption profiles of chemisorbed CO as well as ion scattering and angular resolved X-ray photoelectron spectroscopy (XPS) suggest that the first atomic layer of annealed Pt₃Ti(111) is quasi-pure platinum. Scarcely any (θ ≈ 0.01) dissociation of CO was observed. Minor shifts of vibrational frequencies and desorption temperatures compared to Pt(111) and a p(2 × 2) “reconstruction” of the clean surface reveal some influence of the bulk. Auger spectroscopy, XPS, and ion scattering all show an increased titanium signal as a result of oxidation. Surface bound atomic oxygen gives a vibrational band around 650 cm⁻¹ which coincides with infrared absorption spectra of TiO₂. Flashing with CO shifts the band to 500 cm⁻¹. Correlated with this shift we observe (i) CO₂ desorption at a temperature well above that observed for Pt(111)/O, (ii) an altered Ti XPS signal, and (iii) a reduced oxygen concentration. Subsequently adsorbed CO molecules vibrate at the same frequencies as on the bare surface, give the same c(4 × 2) LEED pattern, and desorb at the same temperatures but with reduced intensity, in all proving that the surface oxide only acts as a site-blocker with respect to the metal surface. Our current understanding of these observations is that oxygen creates “islands of TiO₂”, segregated to the surface but with no electronic influence on remaining areas of the platinum enriched metal surface. The hexacoordinated Ti⁴⁺ ions on the surface of these islands are reduced by CO to pentacoordinated Ti³⁺ species. The vibrational shift, 650 to 500 cm⁻¹, can be understood by the dipole active bands of a triatomic O−Ti⁴⁺ −O vibrator compared to a diatomic Ti³⁺−O vibrator.     

Studies on self-sustained reaction-rate oscillations: I. Real-time surface infrared measurements during oscillatory oxidation of carbon monoxide on platinum

Time-resolved infrared absorption features in the 1800–2400 cm^?1 region during a typical cycle in the oscillatory oxidation of CO over a platinum foil were obtained by Fourier transform infrared reflection absorption spectroscopy. Pretreatment of the foil in an oxidizing environment at high temperatures was found to be necessary to induce large-amplitude, stable oscillations. The oscillations are approximately square-wave in shape, with a high and a low reaction-rate branch. The level of chemisorbed CO in the high reaction-rate branch is typically below the noise level, while in the low reaction-rate branch substantial substantial surface coverages of CO can be observed. No evidence for CO bridge-bonded to the platinum substrate or chemisorbed in the presence of a subsurface Pt oxide could be found at any time during the oscillation cycle. Evidence is presented for the existence of CO islands in the low reaction-rate branch. It is also shown that the low reaction rate realized in this branch is not due to blocking of the surface by chemisorbed CO.     

The adsorption of CO on evaporated iridium films,studied with infrared reflection-absorption spectroscopy

The adsorption of ^12CO on Ir films evaporated under ultrahigh vacuum (UHV) conditions was studied using infrared reflection-absorption spectroscopy (IRAS). Only a single absorption band was observed at 300 K, shifting continuously from the “singleton” value ~2010 cm^?1 at very low coverages to 2093 cm^?1 at saturation coverage. This band is attributed to CO adsorbed on top of the surface atoms. Synchronously with this shift the bandwidth at half maximum intensity $\text{Δv}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ decreases from ~30 to 8 cm^?1. The integrated peak area increases linearly with coverage up to a relative coverage (θ_r) of approximately 0.4, then the increase levels off and a maximum is observed. Upon continuing adsorption the intensity decreases slightly. In addition results are presented on adsorption at 300 K of ¹²CO?¹³CO isotopic mixtures. The coverage induced frequency shift is discussed in terms of a dipole-dipole coupling mechanism and it is concluded that intermolecular coupling can explain the shift (~83 cm^?1) observed. The decrease in intensity at coverages > 0.4 is attributed to the formation of a compressed overlayer with part of the CO molecules adsorbed in a multicentre position with different spectral properties. No infrared bands of nitrogen adsorbed at 78 K could be detected at pressures up to 6.7 kPa (1 Pa = 0.0075 Torr, 1 Torr = 133.32 Pa).     

Absorption properties of infrared active gases at high pressures—II. N2O and CO

Absorptions of the near infrared N₂O and CO bands were measured at high pressures. The band intensities were found to be 0.153 ± 0.002, 1.14 ± 0.01, 1.67 ± 0.01,0.035 ± 0.002, 3.25 ± 0.02 and 49.9 ± 0.3 cm^-1/(atm-cm)_STP for the 2.0, 2.1, 2.3, 2.5, 2.6 and 2.9 μm N₂O bands, respectively, and 2.07 ± 0.02 cm^-1/(atm-cm)_STP for the first overtone CO band. It was also found for both molecules that the spectra measured under large absorber amounts are smaller in the band wings than those calculated from the Lorentzian line profile. This discrepancy is discussed in terms of non-Lorentzian behavior of the line profile.     

Chemisorption of carbon monoxide on platinum {111}: Reflection-absorption infrared spectroscopy

Reflection-adsorption infrared spectroscopy has been combined with thermal desorption and surface stoichiometry measurements to study the structure of CO chemisorbed on a {111}- oriented platinum ribbon under uhv conditions. Desorption spectra show a single peak at coverages > 10¹⁴ molecules cm^?2, with the desorption energy decreasing with increasing coverage up to 0.4 of a monolayer, and then remaining constant at ≈135 kJ mol^?1 until saturation. The “saturation” coverage at 300 K is 7 × 10¹⁴ molecules cm^?2, and no new low temperatures state is formed after adsorption at 120 K. Infrared spectra show a single very intense, sharp band over the spectral range investigated (1500 to 2100 cm^?1), which first appears at low coverages at 2065 cm^?1 and shifts continuously with increasing coverage to 2101 cm^?1 at 7 × 10¹⁴ molecules cm^?2. The halfwidth of the band at 2101 cm^?1 is 9.0 cm^?1, independent of temperature and only slightly dependent on coverage. The band intensity does not increase uniformly with increasing coverage, and hysteresis is observed between adsorption and desorption sequences in the variation of both the band intensity and frequency as a function of coverage. The frequency shift and the virtual invariance of the absorption band halfwidt with increasing coverage (Jespite recent LEED evidence for overlayer compression in this system) are attributed to strong dipole-dipole coupling in the overlayer.     

The forbidden far-infrared ν6 band of SF6

The far infrared spectra of SF₆ in the 33-μm region in the gas phase at different pressures and in the liquid phase have been studied. A small band situated at 351 cm^?1 on the high-frequency side of two difference bands situated at 304.5 cm^?1 has been observed in the gas phase. Since the integrated intensity of the 351-cm^?1 band varies linearly with the density, it cannot be collision induced. It appears that it is the forbidden ν₆ band that becomes active by Coriolis interaction. This band is seen in the liquid at about the same frequency when it is deconvoluted from the neighboring broadened and split difference bands.     

Raman spectroscopic study of the antimonate mineral brandholzite Mg[Sb2(OH)12]·6H2O

Raman spectra of brandholzite Mg[Sb₂(OH)₁₂]·6H₂O were studied, complemented with infrared spectra, and related to the structure of the mineral. An intense Raman sharp band at 618 cm⁻¹ is attributed to the SbO symmetric stretching mode. The low‐intensity band at 730 cm⁻¹ is ascribed to the SbO antisymmetric stretching vibration. Low‐intensity Raman bands were found at 503, 526 and 578 cm⁻¹. Corresponding infrared bands were observed at 527, 600, 637, 693, 741 and 788 cm⁻¹. Four Raman bands observed at 1043, 1092, 1160 and 1189 cm⁻¹ and eight infrared bands at 963, 1027, 1055, 1075, 1108, 1128, 1156 and 1196 cm⁻¹ are assigned to δ SbOH deformation modes. A complex pattern resulting from the overlapping band of the water and hydroxyl units is observed. Raman bands are observed at 3240, 3383, 3466, 3483 and 3552 cm⁻¹; infrared bands at 3248, 3434 and 3565 cm⁻¹. The Raman bands at 3240 and 3383 cm⁻¹ and the infrared band at 3248 cm⁻¹ are assigned to water‐stretching vibrations. The two higher wavenumber Raman bands observed at 3466 and 3552 cm⁻¹ and two infrared bands at 3434 and 3565 cm⁻¹ are assigned to the stretching vibrations of the hydroxyl units. Observed Raman and infrared bands in the OH stretching region are associated with O‐H···O hydrogen bonds and their lengths 2.72, 2.79, 2.86, 2.88 and 3.0 Å (Raman) and 2.73, 2.83 and 3.07 Å (infrared). Copyright © 2009 John Wiley & Sons, Ltd.     

Infrared spectra for co isotopes chemisorbed on Pt “111”: Evidence for strong absorbate coupling interactions

Previous results for ¹²C¹⁶O chemisorbed on a Pt“111” recrystallised ribbon revealed that the infrared absorption band due to the CO stretch appears at low coverages at 2063 cm^?1 and shifts to ~2100 cm^?1 at saturation coverage at 300 K. The cause of this shift is studied in the present work, by investigating the vibrational spectra from a variety of mixtures of ¹²C¹⁶O and ¹²C¹⁶O. The results show that there is a strong dipole-dipole coupling interaction between adsorbate molecules in the overlayer, and provide conclusive evidence that the 35 cm^?1 frequency shift observed with increasing coverage for ¹²C¹⁶O is attributable to coupling.     

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.     

Quantitative Analysis by Derivative Electronic Spectroscopy

Abstract

Absorption and emission spectroscopy in the ultraviolet and visible regions, apart from being the earliest physical techniques of analysis, have great utility in solving a variety of structural and analytical problems [l-41. However, in many cases the quantitative determination of individual components in a mixture by UV-VIS spectroscopy becomes very difficult owing to the spectral similarities and overlapping of weak absorption bands of one component by strong absorption bands of other components. It was recently recognized that derivative spectrophotometry, introduced about three decades ago [5-81 and originally proposed by Rutherford [9], can be a very useful analytical tool for characterizing an analyte band that is overlapped by other absorption bands with different halfwidths. On differentiation, the intensity of the absorption band with a small halfwidth increases more than that of a band with a large halfwidth [10]. The central idea behind the development of the science of derivatized spectra rests upon the measurement of the first or the higher derivatives of the absorbance A or the luminescence intensity I with respect to the wavelength λ, e.g., dI/dλ, dA/dλ, d²I/dλ², etc. These derivatives, when plotted or scanned against wavelength, yield an array of derivative spectra.     

On the Relative Intensity-Concentration Relationship of Carbonyl Bands in the Solution Infrared Spectra of Metal Carbonyl Compounds of C4v Symmetry

The theory on the relative intensities of CO stretching bands of metal carbonyl compounds of C^4v symmetry has been advanced by orgel, inter alios. ² For complexes of formula M(CO)₅Xⁿ [a = -1, 0), three infrared active bands are expected, 2A₁ + E. The two A₁ bands consist of modes which are predominantly vibration of the CO trans to X (A₁ ⁽¹⁾) and the symmetrical stretch of the four equatorial CO's (A^{1 (2)}). The A₁ ⁽²⁾ band is nearly forbidden, and owes its intensity to the contribution of the axial CO stretch to the normal mode. The end result of this coupling between axial and radial CO stretching symmetry modes would appear to be an aid in assigning the bands in the carbonyl stretching region to the appropriate symmetry modes; the relative intensities are weak (A₁ ⁽²⁾), strong (E), and medium (A₁ ⁽¹⁾) Although this weak-strong-medium pattern is invariably observed in the spectra of     

Raman spectroscopic study of the antimonate mineral bottinoite Ni[Sb2(OH)12]·6H2O and in comparison with brandholzite Mg[Sb5+2(OH)12]·6H2O

Raman spectroscopy was used to study the mineral bottinoite and a comparison with the Raman spectra of brandholzite was made. An intense sharp Raman band at 618 cm⁻¹ is attributed to the SbO symmetric stretching mode. The low intensity band at 735 cm⁻¹ is ascribed to the SbO antisymmetric stretching vibration. Low intensity Raman bands were found at 501, 516 and 578 cm⁻¹. Four Raman bands observed at 1045, 1080, 1111 and 1163 cm⁻¹ are assigned to δ SbOH deformation modes. A complex pattern resulting from the overlapping band of the water and hydroxyl units is observed. Raman bands are observed at 3223, 3228, 3368, 3291, 3458 and 3510 cm⁻¹. The first two Raman bands are assigned to water stretching vibrations. The two higher wavenumber Raman bands observed at 3466 and 3552 cm⁻¹ and two infrared bands at 3434 and 3565 cm⁻¹ are assigned to the stretching vibrations of the hydroxyl units. Observed Raman and infrared bands are connected with O H···O hydrogen bonds and their lengths 2.72, 2.79, 2.86, 2.88 and 3.0 Å (Raman) and 2.73, 2.83 and 3.07 Å (infrared). Copyright © 2010 John Wiley & Sons, Ltd.     

The CO fundamental-band laser as secondary frequency standard at 5 µm

We present a very high-resolution heterodyne spectrometer based on a CO laser which operates down to fundamental-band transitions of the molecule. This allows us to detect saturated absorption signals on these transitions at very low pressure (0.4 Pa) and laser intensity (< 1 mW/cm²), yielding a linewidth of about 250 kHz. With the CO fundamental-band laser stabilized to these saturation signals we have measured the transition frequencies of the fundamental bands of three isotopic species to an accuracy of typically 20 kHz (v/v 3 × 10^–10), referenced to the CO₂ frequency standard. Together with additional frequency measurements of the first hot bands, these provide the first heterodyne frequency data of sub-Doppler accuracy for transitions in low lying bands of CO. They now represent the most accurate secondary frequency standard in the spectral region around 5 µm (60 THz).     

Chemisorption of nitrogen on platinum {111}: Reflection-absorption infrared spectroscopy

Reflection-absorption infrared spectroscopy has been combined with thermal desorption and surface coverage measurements to study nitrogen adsorption on a {111}-oriented platinum ribbon under ultrahigh vacuum conditions. Desorption spectra show a single peak (at 180 K) after adsorption at 120 K, giving a coverage-independent activation energy for desorption'of ～40 kJmol^?1. The initial sticking probability at this temperature is 0.15, and the maximum uptake was ～1.1 × 10¹⁴ molecule cm^?2. The adsorbed nitrogen was readily displaced by CO, h₂ and O₂. An infrared absorption band was observed with a peak located at 2238 ± 1 cm^?1, and a halfwidth of 9 cm^?1, with a molecular intensity comparable to that reported for CO on Pt{111}. The results are compared with data for chemisorption on other group VIII metals. An earlier assignment of infrared active nitrogen to B₅ sites on these metals is brought into question by the present results.     

Electronic spectra of potassium bromide containing thallium II. Emission spectrum excited at 2537 Å

The emission spectrum of KBr: Tl⁺ excited at 2537 Å has been measured in the temperature range 15–296°K. At low temperatures the spectrum consists of a prominent band at 4.01 eV, a much smaller band at 3.40 eV and a very small band at 3.15 eV. The last does not appear to change much with temperature and so could not be measured accurately. The temperature-dependence of the two main bands is complex. Between 60 and 100°K the low-energy band increases sharply in intensity, while the high-energy band decreases correspondingly. Above 110°K the situation reverses and the low-energy band decreases in intensity while the high-energy band grows. Both bands closely approximate symmetric Gaussians. The temperature-dependence of the intensity of these two bands is well-explained qualitatively by the existence of two kinds of minima on the adiabatic potential energy surface for the A state. However, predictions of the temperature-dependence of the two emission bands based on calculated adiabatic potential energy surfaces are not in quantitative agreement with the experimental results. Possible reasons for this are our lack of knowledge of precise values for the parameters which enter into the theory, namely the spin-orbit coupling constant, the exchange integral, and the electron lattice coupling constant. The possible role of the ³A_1u state in emission is discussed briefly.     

Absolute frequency measurements of the 2-0 band of CO at 2.3 μm; Calibration standard frequencies from high resolution color center laser spectroscopy

The absolute frequencies of 20 lines of the 2-0 band of CO near 4260 cm^?1 have been measured by heterodyne frequency measurement techniques. Eleven of the lines were measured by saturated absorption techniques which produced linewidths of about 3 MHz. New rovibrational constants have been fitted to these measurements. A table of calculated transition frequencies is given with estimated absolute uncertainties as small as 0.0000023 cm^?1 (70 kHz) near the band center. The pressure shifts of three lines have been measured and fall in the range from ?0.9 to ?3 kHz/Pa (?122 to ?400 kHz/Torr). It is suggested that the generally accepted frequencies of the 1-0 band of CO should be lowered by 7 MHz.     

Normal Unenhanced Raman Spectra of CO and CH4 Adsorbed on Cobalt(poly)

Abstract

Normal unenhanced Raman spectra (NURS) of low-polarizability CO molecules were observed for the first time on cobalt at R. T. and residual gas pressure. We assign five bands observed between 2030–2130 cm^?1 to linear chemisorbed CO species, while those observed between 1840–2010 cm^?1 have been ascribed to the 2-fold chemisorbed species. The three bands observed between 1740–1830 cm^?1 we believe are due to the 3-fold species. The corresponding fourteen Co-C stretches were observed and assigned. A model based upon electron backdonation is proposed for each of the three structures. NURS were also observed at R. T. for physisorbed CH₄ and assignments are made to the four frequencies of CH_4.