High-resolution IR Research Articles

Thermal decomposition of fire retardant brominated epoxy resins

Brominated epoxy resin (BER) containing 20% Br has been prepared by curing a mixture of diglycidylethers of bisphenol A (DGBBA)/tetrabromobisphenol A (DGEBTBA) and 4,4′-diaminodiphenylsulphone (DDS). Its thermal stability has been studied by high resolution thermogravimetry and IR spectroscopy. Programmed heating condition using inert atmosphere has been applied to collect gaseous and high boiling product, which have been identified by means of gas chromatography–mass spectrometry (GC–MS). The mechanism of the thermal decomposition of the resin is discussed.

Further Insights into the Structure of 30 Doradus from the [ITAL]Hubble Space Telescope[/ITAL] Instruments

New observations with the Hubble Space Telescope Wide Field Planetary Camera 2 (WFPC2), combined with prior archival data, provide nearly complete coverage of the inner 30 Doradus Nebula in both nebular lines and continuum at 01 resolution. The developing windblown cavity surrounding the massive first-generation, central cluster and its interface with the remanent molecular clouds, the site of second-generation, triggered star formation, are imaged in their entirety. Dithered Planetary Camera observations with 003 resolution of Knots 1–3 reveal further structural details of the large dust pillars oriented toward the central cluster and the newborn, massive multiple systems of the second generation in those fields. The new data also provide the first WFPC2 coverage of the fields of two interesting, luminous infrared sources observed in our previous Near Infrared Camera and Multi-Object Spectrometer program; comparisons of the high-resolution optical and IR images are illuminating. In addition, we have obtained Space Telescope Imaging Spectrograph optical, long-slit observations of seven O-type multiple systems in the region, including those in Knots 1–3 and four representatives of the older generation. The spatially resolved spectrograms and classifications of the close pairs, with separations ranging from 009 to 118, are presented, as well as WFPC2 photometry of the individual components and the compact clusters of fainter stars associated with them. These new observations, and planned further analysis of them, offer significant new information about the intricate structure and evolution of the two-stage starburst in 30 Dor.

480 × 8 hybrid HgCdTe infrared focal plane arrays for high-definition television format

We explain the technologies used for high-performance long linear arrays based on HgCdTe/CMOS hybrid multiplexers with bidirectional time delay and integration (TDI) functions and describe the development of the first high-resolution IR imaging system with a superextended graphics array (SXGA) format. Long-wavelength IR photodiode arrays are fabricated using liquid-phase epitaxially grown HgCdTe on a CdZnTe substrate. Each photodiode array consists of 480x8 element n+/n-on-p diodes formed by B+ implantation. Diodes with a 10.3-μm cutoff wavelength have a typical zero-bias resistance of 10 MΩ and a shunt resistance of 1 GΩ. Four CMOS readout integrated circuits (ROICs) are used for bidirectional TDI and multiplex operations, where each ROIC sums up and multiplexes eight signals from 120 channels. The ROIC also includes pixel deselection and gain control circuits along with the corresponding memory and writing means. The IR focal plane arrays (IRFPAs) have a typical noise equivalent temperature difference (NETD) of 18 mK after TDI with F/1.55 optics and 10-μs integration. The IR imaging system adopts an interlace scan using the 480x8 element IRFPA to demonstrate a high spatial resolution of 1280 horizontal lines by 960 vertical lines (SXGA format) and an NETD of less than 30 mK. The unique algorithm for image enhancement is successfully confirmed to be efficient.

High-Resolution Spectroscopic Study of Matrix-Isolated Reactive Intermediates: Vibrational Assignments for 3-Fluoro-o-Benzyne and Perfluoro-o-Benzyne∇

A novel “site decompression technique” that takes advantage of specific pressure relaxation effects in cryogenic noble gas matrices was applied in a spectroscopic investigation of the two title compounds, resulting in virtually background-free, complete, high-resolution IR spectra with line widths of ca. 0.1 cm-1. The compounds were prepared photochemically in Ar and Ne matrices and, together with the related intermediates, fluorinated benzocyclopropenone and cyclopentadienylideneketene, characterized by IR and UV−visible absorption spectroscopy. Weak IR absorption bands observed at 1878 cm-1 for perfluoro-o-benzyne and at 1866 cm-1 for 3-fluoro-o-benzyne were assigned to CC triple bond stretching vibrations, corresponding to the transition at 1846 cm-1 in the parent o-benzyne. The application of polarization spectroscopy on photooriented samples led to the determination of transition moment directions for most of the observed vibrational transitions. Absolute IR absorption intensities were also obtained. The assignments of the observed transitions were supported by the results of B3LYP/cc-pVDZ quantum chemical calculations.

Representing Born–Oppenheimer breakdown radial correction functions for diatomic molecules

The empirical determination of Born–Oppenheimer breakdown (BOB) correction functions from the analysis of high resolution diatomic molecule spectra is becoming increasingly common. However, in virtually all applications to date, the analytic expressions used to represent those functions have unphysical limiting behaviour which makes the resulting overall potential energy functions unusable at long-range. This paper delineates the limiting physical constraints, which should be imposed on the form of such BOB correction functions, and presents flexible new expressions incorporating those constraints. The utility of these new forms is illustrated by a re-analysis of recent high resolution IR data for the ground electronic state of AgH, which yields an updated potential energy function and more meaningful adiabatic (potential) and non-adiabatic (centrifugal) BOB correction functions for this system. Further examination of this AgH system also illustrates the problem of model dependence associated with efforts to determine physically unique potential energy and centrifugal BOB correction functions.

Iridoid glucosides from roots of Vietnamese Paederia scandens

Four iridoid glucosides, three of which are dimeric were isolated from the methanol extract of roots of Vietnamese Paederia scandens (Lour) Merrill together with the five known glucosides, paederoside, asperuloside, paederosidic acid, asperulosidic acid and geniposide. Seven sulfur-containing iridoid glucosides were also isolated. The structures of the iridoid glucosides were determined by a combination of high-resolution NMR, MS, IR and UV spectra, and chemical reaction such as acetylation.

Beyond the Born–Oppenheimer approximation: High-resolution overtone spectroscopy of H2D+ and D2H+

Transitions to overtone 2ν2 and 2ν3, and combination ν2+ν3 vibrations in jet-cooled H2D+ and D2H+ molecular ions have been measured for the first time by high-resolution IR spectroscopy. The source of these ions is a pulsed slit jet supersonic discharge, which allows for efficient generation, rotational cooling, and high frequency (100 KHz) concentration modulation for detection via sensitive lock-in detection methods. Isotopic substitution and high-resolution overtone spectroscopy in this fundamental molecular ion permit a systematic, first principles investigation of Born–Oppenheimer “breakdown” effects due to large amplitude vibrational motion as well as provide rigorous tests of approximate theoretical methods beyond the Born–Oppenheimer level. The observed overtone transitions are in remarkably good agreement (<0.1 cm−1) with non-Born–Oppenheimer ab initio theoretical predictions, with small but systematic deviations for 2ν2, ν2+ν3, and 2ν3 excited states indicating directions for further improvement in such treatments. Spectroscopic assignment and analysis of the isotopomeric transitions reveals strong Coriolis mixing between near resonant 2ν3 and ν2+ν3 vibrations in D2H+. Population-independent line intensity ratios for transitions from common lower states indicate excellent overall agreement with theoretical predictions for D2H+, but with statistically significant discrepancies noted for H2D+. Finally, H2D+ versus D2H+ isotopomer populations are analyzed as a function of D2/H2 mixing ratio and can be well described by steady state kinetics in the slit discharge expansion.

Energy-Dependent Quantum-State-Resolved Relaxation of Highly Vibrationally Excited Pyridine (Evib = 36 990−40 200 cm-1) through Collisions with CO2

The energy dependence of strong collisional deactivation that transfers energy from highly vibrationally excited pyridine to a CO 2 bath has been investigated for pyridine with internal energy between E v i b = 36 990 and 40 200 cm - 1 . Highly excited pyridine was prepared by absorption of tunable pulsed UV laser light at four wavelengths, λ = 251, 259, 266, and 273 nm, followed by prompt radiationless decay from S 1 (or S 2 ) to the vibrationally excited levels of the ground electronic state. High-resolution transient IR absorption spectroscopy was used to measure the nascent rotational and translational energy distributions of scattered CO 2 molecules in high J states of the ground vibrationless (00 0 0) level that result from collisions with hot pyridine. Our results reveal that substantial amounts of rotational and translational energy are imparted to CO 2 (00 0 0) molecules for all four pyridine energies and that the magnitude of the CO 2 rotational and translational energy gains changes very little for a 3000 cm - 1 change in the vibrational energy of the pyridine donor. State-resolved energy-transfer rate constants were measured at each UV wavelength and were also found to be fairly insensitive to changes in the donor internal energy content for the excitation energies studied here. These results indicate that the relaxation mechanism and the energy-transfer probability distribution function for the V → RT pathway for pyridine(E)/CO 2 collisions are invariant to this change in internal energy. A consideration of energy-transfer rates using Fermi's Golden Rule is consistent with the observed behavior. Comparison with previous energy-dependent collisional quenching studies [Elioff, M. S.: Wall, M.; Lemoff, A.; Mullin, A. S. J. Chem. Phys. 1999, 110, 5578-5588] on vibrationally hot pyrazine with CO 2 suggests that this may be a general phenomenon in the collisional relaxation of highly excited molecules.

Mars Express Mission and Astrobiology

A short description of the ESA Mars Express mission planned for 2003 is given. The main goal of the mission is to look for traces of life with direct (in situ) or indirect (from orbit) measurements. The Isidis Planitia area was preliminary selected to be the landing site of Beagle-2, a small lander module for geologic, meteorologic, and exobiologic studies. In particular, one instrument on Beagle-2 will measure the carbon ratio 12C/13C, which should indicate the existence of extinct life. Over a period of one Martian year, the Mars Express orbiter will perform global high-resolution (10 m) imaging and global IR mineralogical mapping. Close international cooperation, including scientific data exchange and analysis, is foreseen.

Differential scattering dynamics of F+CH 4→HF( v, J)+CH 3 via high-resolution IR laser dopplerimetry

Product recoil data from F+CH 4→HF( v, J)+CH 3 reactive scattering are obtained using crossed supersonic jets and narrow band ( Δν≈0.0001 cm −1 ) infrared radiation laser direct absorption techniques. The high-resolution infrared radiation profiles of HF( v, J) product exhibit extensive Doppler broadening that directly reflects quantum state-resolved translational distributions in the laboratory frame under single collision conditions. Analyses of Doppler profiles yield information on state-resolved differential cross sections into the HF( v=1) and HF( v=2) vibrational manifolds, which both identify a propensity for forward/backward scattering (|cos( θ)|≈1) over side scattering (|cos( θ)|≈0) in the center-of-mass frame.

High-resolution IR studies of hydrogen bonded clusters: large amplitude dynamics in (HCl)n.

Structural and dynamical information on small hydrogen-bonded systems is revealed by high-resolution IR spectroscopy of HCl dimer, trimer and tetramer. In (HCl)2, four combination bands tentatively assigned to the Van der Waals stretch nu 4 and geared band nu 5 vibrations are observed. The study focuses on two unexpected results: (i) all of the observed bands are built only on the bound HCl stretch nu 2, and (ii) the bands predominantly originate from the 9-fold less populated upper tunneling level of the ground state. Model 3D quantum calculations are presented to show that both these surprising trends originate from the large amplitude tunneling dynamics in the dimer. The (HCl)3 spectra are assigned and analyzed for multiple isotopomeric contributions. The spectral fit reveals large homogeneous line broadening indicating the excited state lifetime of approximately 1.6 ns and tentatively associated with dynamics of intramolecular vibrational energy distribution (IVR) induced trimer ring opening. Finally, first high-resolution data on the HCl stretch fundamental spectrum of (HCl)4 are presented.

Trace-gas detection in ambient air with a thermoelectrically cooled, pulsed quantum-cascade distributed feedback laser

A pulsed quantum-cascade distributed feedback laser operating at near room temperature was used for sensitive high-resolution IR absorption spectroscopy of ambient air at a wavelength of approximately 8 microm. Near-transform-limited laser pulses were obtained owing to short (approximately 5-ns) current pulse excitation and optimized electrical coupling. Fast and slow computer-controlled frequency scanning techniques were implemented and characterized. Fast computer-controlled laser wavelength switching was used to acquire second-derivative absorption spectra. The minimum detectable absorption was found to be 3 x 10(-4) with 10(5) laser pulses (20-kHz repetition rate), and 1.7 x 10(-4) for 5 x 10(5) pulses, based on the standard deviation of the linear regression analysis.

ITAL]Chandra[/ITAL] X-Ray Observatory Detection of Extended X-Ray Emission from the Planetary Nebula BD +30°3639

We report the detection of well-resolved, extended X-ray emission from the young planetary nebula BD +30°3639 using the Advanced CCD Imaging Spectrometer (ACIS) aboard the Chandra X-ray Observatory. The X-ray emission from BD +30°3639 appears to lie within, but is concentrated to one side of, the interior of the shell of ionized gas seen in high-resolution optical and IR images. The relatively low X-ray temperature (TX ~ 3 × 106 K) and asymmetric morphology of the X-ray emission suggest that conduction fronts are present and/or mixing of shock-heated and photoionized gas has occurred, and furthermore hints at the presence of magnetic fields. The ACIS spectrum suggests that the X-ray-emitting region is enriched in the products of nuclear burning. Our detection of extended X-ray emission from BD +30°3639 demonstrates the power and utility of Chandra imaging as applied to the study of planetary nebulae.

Experimental and Theoretical Spectroscopic Studies on Selected Igepals

m H2 m +1)-C6H4(OCH 2 CH 2 ) n OH were investigated by high resolution NMR and IR spectroscopy. Gauge invariant atomic orbital density functional theory NMR calculations on model molecules in the gas phase additionally supported the assignment of experimental carbon signals. Different orientations of individual sub-units of an aliphatic chain relative to external magnetic field and trans-gαuche transitions were assumed to explain complex patterns of carbon spectra in the aliphatic region of igepals with linear alkyl chain.

Quantum state-resolved reactive scattering of F+CH4→HF(v,J)+CH3: Nascent HF(v,J) product state distributions

State-to-state reactive scattering of F+CH4→HF(v,J)+CH3 is studied using crossed supersonic jets and high-resolution (Δν≈0.0001 cm−1) IR laser direct absorption techniques. Rovibrational state-resolved HF column-integrated absorption profiles are obtained under single collision conditions and converted to populations via appropriate density-to-flux transformation. Nascent rovibrational distributions in each HF(v,J) state are reported. Summed over all product rotational levels, the nascent vibrational quantum state populations for HF(v) [(v=3) 0.106(3); (v=2) 0.667(14); (v=1) 0.189(27); (v=0) 0.038(78); 2σ error bars] are in agreement with previous flow cell studies by Setser, Heydtmann, and co-workers [Chem. Phys. 94, 109 (1985)]. At the rotational state level, however, the current studies indicate nascent distributions for HF(v,J) that are significantly hotter than previously reported, ostensibly due to reduced collisional relaxation effects under supersonic jet conditions. Final HF rotational states from F+CH4 are observed near the maximum energetically accessible J values in both the v=2 and v=3 vibrational manifolds, which provides experimental support for a bent F–H–C transition state structure.

High-Resolution Infrared Absorption Spectroscopy of C60 Molecules and Clusters in Parahydrogen Solids

We report the isolation of C60 molecules in cryogenic parahydrogen (pH2) solids by the rapid vapor deposition method. New theoretical simulations of rovibrational spectra for low-temperature isolated 12C60 molecules, including boson-exchange symmetry restrictions on the rotational levels, predict a characteristic “null gap” and unequal rotational line spacings for low-J values. High-resolution IR absorption spectra of the C60/pH2 samples failed to show rotationally resolved features, and in fact suggest that the majority of the C60 molecules are not rotating. However, spectra of the F1u(1) vibrational mode near 530 cm-1 show line widths of ≈0.2 cm-1 fwhm, the sharpest IR absorption bands for C60 reported to date. Visible absorption spectra also show sharp features in the ≈600 nm region, supporting our contention of well-isolated C60 molecules. The C60 molecules appear to stabilize the pH2 solid, inhibiting the fcc to hcp conversion which usually occurs upon annealing of rapid vapor deposited pH2 solids to...

The ν1=1 and ν3=1 states of AsF3 studied by high resolution IR and millimeterwave spectroscopy: the equilibrium structure of AsF3

The high resolution (0.0025cm−1) infrared spectrum of AsF3 in the ν1 (ν0 740.5708cm−1) and ν3 region (ν0 702.5650cm−1) was recorded and rotationally analyzed. Millimeterwave transitions within the ν1=1 and ν3=1 states were measured in the 340–470GHz region. Owing to the observation of numerous perturbation-allowed transitions in the ν3 band, which are caused by r resonance effects occurring for different K values, C0, DK0 and HK0 have been determined. All experimental observations on ν1 and ν3 have been fitted together employing two different and equivalent reductions of the rovibrational Hamiltonian, one constraining q3 and the other one BΩζ13y to zero. A significantly improved re structure of AsF3 has been determined, re(AsF) 1.7043(2) Å and αe(FAsF) 95.88(4)°.

Vibrational Assignment of All 46 Fundamentals of C60 and C606-: Scaled Quantum Mechanical Results Performed in Redundant Internal Coordinates and Compared to Experiments

Traditional vibrational assignment in terms of bond stretching, angle bending, and torsion is not possible in fullerenes due to the very large number of coupled internal coordinates. Large scale density functional calculations of the vibrational properties of C60 and C606- have been carried out with Becke3LYP and BeckeLYP exchange-correlation functionals in the pursuit of obtaining a reliable set of 174 normal modes (46 fundamental frequencies) and understanding the effect of charge transfer (doping) on the vibrational modes. The calculations involve scaling of the force field in redundant internal coordinates as proposed by Pulay et al. The scaled quantum mechanical (SQM) calculations yield excellent agreement with experiment for the 14 allowed frequencies. This provides the basis for an accurate assignment of all nonallowed fundamentals and the reassignment of the observed overtone and combination bands of the high-resolution Raman (Wang et al., 1993) and IR (Martin et al. 1994) spectra. The calculated intensity ratios for the four IR active bands agree with experiment. The large IR intensity enhancements observed for C606- relative to C60 are explained by the enhancement of certain components of the atomic polar tensor that is partially due to bond equalization in the charged fullerene. This enhancement appears to be largely a molecular rather then a solid state effect.

The determination of the cummingtonite content of synthetic tremolite

Amphiboles of predominantly tremolite composition have been synthesized at 670-800 degrees C and 200-700 MPa in the system CaO-MgO-SiO 2 -H 2 O. The tremolite crystals were large enough to be analyzed by electron microprobe. The run products were also studied by scanning electron microscopy, high resolution electron microscopy, X-ray diffraction (Rietveld analysis) and IR spectroscopy. The electron microprobe analyses resulted in average compositions between tr 87 cum 13 and tr 99 cum 1 . The cummingtonite contents determined by electron microprobe varied by up to + or -7 mol% within each run. Investigations using high resolution electron microscopy revealed that the tremolite-cummingtonite solid solutions were highly ordered and chain multiplicity faults were rare. Although the lattice parameters a, b and beta are expected to be a function of the cummingtonite content, no correlations were observed between the compositions derived by electron microprobe and the lattice parameters. The energy and absorbance of the OH stretching vibration is a function of M4 site occupancy. Therefore, the cummingtonite content was determined precisely by IR spectroscopy. At least 3 different bands at distinct energies were identified: 3674.6 cm (super -1) for the CaCa-CaCa and 3669.3 and 3672.2 cm (super -1) for the MgCa-CaCa and CaCa-MgCa configurations, respectively. The relative integral absorbances showed that all synthesized amphiboles had cummingtonite contents lower than 6 mol%. In some cases nearly pure tremolite was synthesized (tr 99 cum 1 ). This amount is considerably less than the 10 mol% cummingtonite content (tr 90 cum 10 ) often claimed for synthetic tremolite. The compositions derived by IR spectroscopy correlate with the lattice parameters. Using these correlations the lattice parameters of pure tremolite were extrapolated to be a = 9.8354(18) Aa, b = 18.0562(14) Aa, c = 5.2768(6) Aa, beta = 104.74(2) degrees , V = 906.3(2) Aa 3 .

High-Resolution IR Spectrum of SCF2 from 1000 to 1400 cm−1: The ν1/ν3 + 2ν5/ν2 + ν3 and ν4/ν2 + ν5 Interacting States

The infrared spectrum of SCF2 was recorded in the 1000–1400 cm−1 region with a resolution of 2.5 × 10−3 cm−1. The rotationally resolved ν1 and ν4 band systems were studied for the first time, and altogether 11 500 transitions were assigned. Both fundamentals are involved in strong anharmonic (Fermi) resonances. Effective centers (J = Ka = Kc = 0) of the interacting bands are ν1 1366.7117 cm−1, ν3 + 2ν5 1365.4257 cm−1, ν2 + ν3 1311.1491 cm−1 (a1 species), and ν4 1190.0839 cm-1, ν2 + ν5 1217.8191 cm−1 (b1 species). The strong Ka dependence of the ν1/ν3 + 2ν5 level mixing enabled a numerical determination of the interaction constants while the other anharmonic interactions were accounted for by consideration of relative intensities. Deperturbed band centers, anharmonicity constants, and equilibrium and excited state rotational and centrifugal distortion constants were determined.