Infrared Absorption Features Research Articles

New Narrow Infrared Absorption Features in the Spectrum of Io between 3600 and 3100 cm -1 (2.8-3.2 μm)

We report the discovery of a series of infrared absorption bands between 3600 and 3100 cm -1 (2.8-3.2 μm) in the spectrum of Io. Individual narrow bands are detected at 3553, 3514.5, 3438, 3423, 3411.5, and 3401 cm -1 (2.815, 2.845, 2.909, 2.921, 2.931, and 2.940 μm, respectively). The positions and relative strengths of these bands, and the difference of their absolute strengths between the leading and trailing faces of Io, indicate that they are due to SO 2. The band at 3438 cm -1 (2.909 μm) could potentially have a contribution from an additional molecular species. The existence of these bands in the spectrum of Io indicates that a substantial fraction of the SO 2 on Io must reside in transparent ices having relatively large crystal sizes. The decrease in the continuum observed at the high frequency ends of the spectra is probably due to the low frequency side of the recently detected, strong 3590 cm -1 (2.79 μm) feature. This band is likely due to the combination of a moderately strong SO 2 band and an additional absorption from another molecular species, perhaps H 2O isolated in SO 2 at low concentrations. A broad (FWHM ≈ 40-60 cm -1), weak band is seen near 3160 cm -1 (3.16 μm) and is consistent with the presence of small quantities of H 2O isolated in SO 2-rich ices. There is no evidence in the spectra for the presence of H 2O vapor on Io. Thus, the spectra presented here neither provide unequivocal evidence for the presence of H 2O on Io nor preclude it at the low concentrations suggested by past studies.

Surface Cleaning, Topography, and Temperature Measurements of Single Crystal Diamond

ABSTRACTApplication of surface science methods to single crystal diamond surfaces requires the preparation of clean, well-ordered surfaces and accurate measurement of substrate temperature. Cleaning of diamond (100) in H2SO4/HNO3/HClO4 produced several infrared absorption features between 1025 and 1275 cm-1, as observed by infrared multiple-internal-reflection spectroscopy. These modes are assigned to surface hydroxyl and bridge-bonded oxygen. Heating an oxidized surface to ca. 1130 °C caused disappearance of a surface hydroxyl mode centered at 1080 cm-1. We show by atomic force microscopy that an as-polished diamond (100) sample is covered by grooves and ridges several nm in height, implying a modest density of atomic steps. The surface of a diamond that underwent etching via numerous adsorption/desorption experiments in ultrahigh vacuum and was acid cleaned several times was essentially unchanged, indicating a minimal perturbation of the surface topography. The capability of Fizeau interferometry for accurate measurement of single-crystal diamond temperatures is demonstrated.

Spectroscopic detection of molecular hydrogen frozen in interstellar ices.

A weak infrared absorption feature near 4141 wavenumbers (2.415 micrometers) in the spectrum of WL5, an infrared source in the rho Ophiuchus cloud complex, has been detected. It is attributed to molecular hydrogen created by irradiation and frozen in situ into water-rich ices. A second, broader absorption at 4125 wavenumbers centimeters (2.424 micrometers) is probably due to methanol in the ices. The column densities of frozen molecular hydrogen and methanol are inferred to be about 2.5 x 10(18) and 3.0 x 10(19), respectively. There is about three times more frozen molecular hydrogen than frozen carbon monoxide along this line of sight.

Critical-point phonon frequencies of diamond.

The phonon-dispersion curves derived from neutron-scattering experiments performed on diamond [J. Warren et al., Phys. Rev. 158, 805 (1967)] are not accurate enough to yield the exact frequencies of critical-point (CP) phonons and, thus, to provide a satisfactory interpretation of second-order optical spectra. A self-consistent analysis of such spectra [S. Solin and A. Ramdas, Phys. Rev. B 1, 1687 (1970)] was not fully successful because of ambiguities that arise in assigning second-order infrared absorptions and features in the Raman spectra to specific two-phonon summations. A more effective method for obtaining accurate CP phonon frequencies involves investigating defect-activated one-phonon absorptions; in this paper, we take advantage of the availability of chemically vapor-deposited (CVD) diamond for the purpose of locating and assigning infrared (ir) absorption features in the one-phonon region to CP phonons at the Brillouin-zone boundary. Fourier-transform ir absorbance spectra of CVD diamond exhibit a complex structure at wave numbers below the 1332.5-${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ lattice-mode cutoff, which is induced by impurity-associated defect centers and yields the exact positions of 16 zone-edge CP phonons. In conjunction with the triply degenerate zone-center mode, this set of phonons then provides the basis for predicting the positions of second-order optical features through simple summations. When the selection rules are taken into account, the procedure yields excellent results, not only in terms of CVD-diamond ir spectra, but also in regard to earlier measurements of the intrinsic two-phonon absorption coefficient of type-IIa natural diamond [J. Hardy and S. Smith, Philos. Mag. 6, 1163 (1961)] and the second-order polarization-dependent Raman spectra recorded by Solin and Ramdas.

Comparison of Trichlorosilane and Trichlorogermane Decomposition on Silicon Surfaces Using FTIR Spectroscopy

ABSTRACTFourier transform infrared (FTIR) transmission spectroscopy was used to compare the decomposition of trichlorosilane (SiHCl3) and trichlorogermane (GeHCl3) on silicon surfaces. Chlorosilanes, such as SiHCl3 are employed in silicon chemical vapor deposition (CVD). Chlorosilanes and chlorogermanes are also possible molecular precursors for the controlled atomic layer growth of silicon and germanium. GeHCl3 may be useful for the deposition of germanium on silicon surfaces and the growth of Si1−xGex heterostructures. The FTIR studies were performed in-situ in an ultra-high vacuum chamber on high surface area, porous silicon samples. The FTIR spectra revealed that SiHCl3 dissociatively adsorbs at 200 K to form SiH, SiClx, ClSiH and Cl2SiH surface species. The presence of ClxSiH species is revealed by ClxSiH stretching (2196 cm−1) and bending (775, 744 cm−1) vibrations. The presence of these modes indicates that there is incomplete decomposition of SiHCl3 upon adsorption at 200 K. GeHCl3 also dissociatively adsorbs at 200 K to form SiH and SiClx species. An infrared absorption feature in the Ge-H stretching region (1970–1995 cm−1) was not detected in the FTIR spectrum. The absence of a Ge-H absorption feature argues that there is a complete transfer of hydrogen from germanium to surface silicon atoms at 200 K. The thermal stabilities of the surface species were studied with annealing experiments. The Clx SiH formed upon initial SiHCl3 exposures at 200 K were observed to decompose between 200–590 K and form additional surface SiH and SiCl species. For both GeHCl3 and SiHCl3 dissociative adsorption on porous silicon, the SiCL. (x = 2 or 3) surface species were converted to silicon monochloride surface species between 200–600 K. In addition, SiH surface species were lost upon annealing between 680–780 K as H2 desorbed from the surface. The adsorption kinetics of SiHCl3 and GeHCl3 were also monitored on porous silicon at various isothermal temperatures. These experiments provide insight into the surface chemistry of chlorosilanes and chlorogermanes during CVD and atomic layer controlled growth.

Calculation of Optical Conductivity of the Polaron in High Tc Superconductors

By undergoing Varma's phenomenological constraints a calculation of the optical conductivity σ(ω) in polaron model has been performed in order to interpret the infrared absorption features in high Tc superconductors. The temperature and phonon relaxation effects have been included. The agreement between our theoretical results and experiments is satisfactory.

Optical absorption of polarons in high-T c superconductors

A calculation of the optical absorption of the polarons undergoing Varma's phenomenological constraints has been performed in order to interpret the infrared absorption features in high- T c superconductors. The temperature and phonon relaxation effects on the absorption are calculated. It is suggested that the normal-state carriers in the superconducting state are responsible for the absence of the expected absorption onset shift in the experiments. It seems that this model can satisfactorily interpret the infrared absorption features in high- T c superconductors.

Infrared absorption features for tetrahedral ammonia ice crystals

We have computed extinction cross sections for 0.5- and 1-μm volume-equivalent radius tetrahedral NH 3 ice crystals with and without nonabsorbing foreign cores to determine how particle shape and composition affect the strength and shape of resonant absorption features at 9.4 and 26 μm. The peak of the resonance is shifted relative to that for spherical particles, the maximum is smaller (except for 1-μ particles at 9.4 μm), and the integrated strength of the absorption falls in approximate proportion to the volume fraction of the core. It appears that small ( r < 5 μm) NH 3 particles cannot be the principal component of the Jovian haze in the 300- to 500-mbar region.

Excitations of a diamagnetic hole state in the copper-oxide superconductors.

The strong infrared (ir) absorption features observed in the copper oxide superconductors are interpreted to be internal electronic and vibrational excitations of a spin-zero charge-transfer complex (${P}^{+}$) formed between a hole and an essentially single paramagnetic square planar Cu${\mathrm{O}}_{4}$ unit (${P}^{0}$). The large magnitude and bimodal frequency dependence of the electronic polarizability implied by the ir data for ${P}^{+}$ favors a combined excitonic and "charged phonon" mechanism for superconductivity. It is possible that the carriers of the superconductivity are the highly correlated electrons belonging to the ${P}^{0}'\mathrm{s}$, while the ${P}^{+}'\mathrm{s}$ play the role of highly polarizable impurities. The ${P}^{+}'\mathrm{s}$ can delocalize as band polarons.

Characterisation of poly (phenylenevinylene) by infrared and optical absorption

In this paper we present the results of a study of the optical properties of poly (phenylenevinylene), PPV, prepared by the sulphonium polyelectrolyte precursor. We investigate the conditions for the transformation reaction from precursor to PPV using optical and IR absorption. We investigate also the effects of oxidative doping. In situ electrochemical doping shows the appearance of new absorption features at 0.9 and 2.3 eV which correlate with π-π ∗ interband bleaching at 3.0 eV and which may be assigned to valence band to bipolaron level transitions. Chemical doping with iodine and with AsF 5 introduces new infrared absorption features at 1151, 1286, 1317, 1420 and 1506 cm -1.

Real time surface infrared spectroscopy in the study of surface reaction kinetics

With recent improvements in both Fourier Transform and dispersive infrared spectrometers, surface sensitivities have been achieved which are sufficient for time-resolved surface infrared Spectroscopy. This time-resolved capability, along with high spectral resolution (better than 10 cm −1 ), and the ability to probe through high ambient pressures, has enabled infrared spectroscopy to be successfully applied to the study of surface reaction kinetics. For example, time-resolved infrared absorption features in the 1200 cm −1 to 2300 cm −1 region were used in an investigation of oscillatory oxidation of carbon monoxide over a platinum foil catalyst under ambient pressures up to 600 Torr. Adsorbed carbon monoxide and gas-phase carbon dioxide were measured simultaneously, with time resolution of 600 msec per spectrum. In addition, broadband reflectance measurements were used to infer adsorbed oxygen levels from the same real time spectra. These measurements indicated a slow, periodic variation in the number of active sites on the catalyst, in phase with the variations in reaction rate. Parallel studies (Auger and IR) of a Pt foil in UHV suggested that periodic variation in the surface carbon level drives the activity and reaction rate oscillations. The time resolution and high pressure capability of surface infrared Spectroscopy were critical for achieving in-situ measurements on all relevant time scales. Other recents applications of surface infrared spectroscopy, including improvements in time resolution (down to tens of milliseconds per spectrum) will also be discussed.

Observation of several chlorine nitrate (ClONO2) bands in stratospheric infrared spectra

Four of the most prominent and sharpest infrared absorption features of chlorine nitrate at 780.2, 807.7, 809.4 and 1292.6 cm−1 have been observed in a series of infrared solar spectra obtained at an unapodized spectral resolution of 0.01 cm−1, using the Atmospheric Trace Molecule Spectroscopy (ATMOS) instrument from on‐board Spacelab 3.A quantitative analysis of the ν4 Q branch at 780.2 cm−1 has provided insight into the concentration of ClONO2 between 19 and 40 km altitude. While the mean profile deduced from 3 sunset occultations near 30° N latitude exhibits a shape close to that predicted by model calculations, its conconcentrations in the 20 to 32 km altitude range are, however, about 30% larger, reaching a peak concentration of 9 × 108 molecules/cm³ at 25 km. The concentrations above 32 km, deduced from one sunrise occultation at 47° S, are even larger than the corresponding sunset values at 30° N latitude. Some of these discrepancies may be caused by the rather large uncertainty in the assumed Q branch strength.The results reported here constitute a significant input towards understanding the chemistry prevailing in the stratosphere as well as for model calculations predicting the secular evolution of our atmosphere.

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.

On the formation of cavitylike small-polaronic states in solid deuterium

Certain infrared absorption features in tritiated as well as proton-irradiated samples of solid deuterium have been attributed to the formation of bubblelike electronic states localized in the lattice. These bubblelike states are shown to be energetically stable in the Wigner–Seitz model of the crystal and the gap between the ground-state energies in the bubble and the quasi-free states of the electron is calculated. An initial trapping of the electron by a vacancy is assumed in calculating the localized state energy. Calculations based on a continuum model of the solid yield the radius of such bubbles to close agreement with that obtained from the observed Stark shift of the vibrational levels of the neighbouring molecules due to the localized electrons. The model is used to interpret the radiation-induced absorption in proton-irradiated solid deuterium in the spectral region 4000–7500 cm−1.

Optical constants of organic tholins produced in a simulated Titanian atmosphere: From soft x-ray to microwave frequencies

As part of a continuing series of experiments on the production of dark reddish organic solids, called tholins, by irradiation of cosmically abundant reducing gases, the synthesis from a simulated Titanian atmosphere of a tholin with a visible reflection spectrum similar to that of the high altitude aerosols responsible for the albedo and reddish color of Titan has been reported (C. Sagan and B. N. Khare, 1981, Bull. Amer. Astron. Soc. 13, 701; 1982 , Orig. Life. 12, 280) and [C. Sagan, B. N. Khare, and J. Lewis, in press. In Saturn (M. S. Matthews and T. Gehrels, Eds.), Univ. of Arizona Press, Tucson]. The determination of the real ( n) and imaginary ( k) parts of the complex refractive index of thin films of such tholin prepared by continuous D.C. discharge through a 0.9 N 2/0.1 CH 4 gas mixture at 0.2 mb are reported. For 250 A ̊ ≤ γ ≤ 1000 μ m, n and k have been determined from a combination of transmittance, specular reflectance, interferometric, Brewster angle, and ellipsometric polarization measurements; experimental uncertainties in n are estimated to be ±0.5, and in k ± 30%. Values of n(≅1.65) and k (≅0.004 to 0.08) in the visible range are consistent with deductions made by ground-based and spacecraft observations of Titan. Maximum values of k (≅0.8) are near 1000 Å, and minimum values (≅4 × 10 −4) are near 1.5 μm. Many infrared absorption features are present in k( γ), including the 4.6-μm nitrile band.

The organic aerosols of Titan

A dark reddish organic solid, called tholin, is synthesized from simulated Titanian atmospheres by irradiation with high energy electrons in a plasma discharge. The visible reflection spectrum of this tholin is found to be similar to that of high altitude aerosols responsible for the albedo and reddish color of Titan. The real (n) and imaginary (k) parts of the complex refractive index of thin films of Titan tholin prepared by continuous D.C. discharge through a 0.9 N 2/0.1 CH 4 gas mixture at 0.2 mb is determined from x-ray to microwave frequencies. Values of n ( ⋍1.65) and k ( ⋍0.004 to 0.08 ) in the visible are consistent with deductions made by ground-based and spaceborne observations of Titan. Many infrared absorption features are present in k(λ), including the 4.6 μm nitrile band. Molecular analysis of the volatile component of this tholin was performed by sequential and non-sequential pyrolytic gas chromatography/mass spectrometry. More than one hundred organic compounds are released; tentative identifications include saturated and unsaturated aliphatic hydrocarbons, substituted polycyclic aromatics, nitriles, amines, pyrroles, pyrazines, pyridines, pyrimidines, and the purine, adenine. In addition, acid hydrolysis produces a racemic mixture of biological and non-biological amino acids. Many of these molecules are implicated in the origin of life on Earth, suggesting Titan as a contemporary laboratory environment for prebiological organic chemistry on a planetary scale.

Broad infrared absorption feature in solidD2andH2containing tritium

A new infrared absorption feature in the low-temperature spectrum of solid ${\mathrm{D}}_{2}$ and ${\mathrm{H}}_{2}$ containing small amounts of tritium has been observed. The absorption can be interpreted as being due to electrons in bubblelike structures with diameters of approximately 9 \AA{}.

Studies of proton-irradiated cometary-type ice mixtures

Radiation synthesis has been proposed as a mechanism for changing the nature of the outer few meters of ice in a comet stored 4.6 billion years in the Oort cloud and may explain some of the differences observed between new and more evolved comets. Cometary-type ice mixtures were studied in a laboratory experiment designed to approximately simulate the expected temperature, pressure, and radiation environment of the interstellar Oort cloud region. The 2.5- to 15-μm infrared absorption features of thin ice films were analyzed near 20°K before and after 1 MeV proton irradiation. Various ice mixtures included the molecules H 2O, NH 3, CH 4, N 2, C 3H 8, CO, and CO 2. All experiments confirm the synthesis of new molecular species in solid phase mixtures at 20°K. The synthesized molecules, identified by their infrared signatures, are C 2H 6, CO 2, CO, N 2O, NO, and CH 4 (weak). Synthesized molecules, identified by gas chromatographic (GC) analysis of the volatile fraction of the warmed irradiated ice mixture, are C 2H 4 or C 2H 6, and C 3H 8. When CH 4 is present in the irradiated ice mixture, long-chained volatile hydrocarbons and CO 2 are synthesized along with high-molecular-weight carbon compounds present in the room temperature residue. Irradiated mixtures containing CO and H 2O synthesize CO 2 and those CO 2 and H 2O synthesize CO. Due to radiation synthesis, ∼1% of the ice was converted into a nonvolatile residue containing complicated carbon compounds not present in blank samples. These results suggest that irrespective of the composition of newly accreted comets, initial molecular abundances can be altered and new species created as a result of radiation synthesis. Irradiated mixtures exhibited thermoluminescence and pressure enhancements during warming; these phenomena suggest irradiation synthesis of reactive species. Ourbursts in new comets resulting from similar radiation induced exothermic activity would be expected to occur beginning at distances of the order of 100 AU.

A correlation between the infrared absorption features and the low temperature thermal conductivity of different types of natural diamonds

The low-temperature thermal conductivity of three different types of natural diamond has been measured between 0.5 and 20K. It has been attempted to relate the infrared absorption features of the diamonds with their thermal conductivity. A diamond with only B features (i.e. no B' peak) in the infrared was found to contain aggregates with a mean diameter of about 44-65 AA and to have a concentration of about 1014 aggregates per cm3 from a fit of the conductivity curve. Electron microscope pictures showed aggregates of about 50 AA diameter with this concentration. These results tend to confirm a recent suggestion made by T.Evans, that the B features are due to larger (rather than very small) nitrogen aggregates.

Prebiotic polymers and infrared spectra of galactic sources

INFRARED absorption features characteristic of molecular dust clouds in the Galaxy may be assigned to complex organic polymers or prebiotic polymers. It could be argued that such highly stable, complex polymers evolve due to radiation processing of molecular mantles on interstellar grains—essentially by a type of natural selection which operates in the interstellar medium. A large fraction of all C, N, O elements in the interstellar medium could be condensed in the form of these stable polymers. Such interstellar material may also account for a significant fraction of the ‘insoluble organic matter’ which is found in carbonaceous chondrites.