Study of the Fundamental Bands of GeD4 by High-Resolution Raman and Infrared Spectroscopy: First Experimental Determination of the Equilibrium Bond Length of Germane

The four fundamental bands of ⁷⁰GeD₄ have been analyzed using the STDS software developed in Dijon (http://www.u-bourgogne.fr/LPUB/sTDS.html). Both infrared and Raman spectra were used to observe all fundamental bands. Infrared spectra of monoisotopic ⁷⁰GeD₄ were recorded in the regions 600 and 1500 cm⁻¹ using the Bruker 120HR interferometer at Wuppertal. The resolution (1/maximum optical path difference) was between 2.3 and 3.3×10⁻³ cm⁻¹ for the ν₃ and ν₄ infrared-active fundamental bands as well as for the interacting ν₂ band. A high-resolution stimulated Raman spectrum of the ν₁ band has been recorded in Madrid. The instrumental resolution of the Raman spectrum was 3.3×10⁻³ cm⁻¹. We have performed a global fit of the ground state, ν₂/ν₄ bending dyad, and ν₁/ν₃ stretching dyad. We have used 1146, 139, and 676 assigned lines for ν₂/ν₄, ν₁, and ν₃, respectively. The standard deviation is 2.2×10⁻³ cm⁻¹ for the bending dyad, 1.6×10⁻³ cm⁻¹ for the ν₃ infrared lines, and 1.7×10⁻³ cm⁻¹ for the ν₁ Raman lines. These results enabled us to perform the first experimental determination of the equilibrium bond length of germane as r_e=1.5173(1) Å.     

Emission spectroscopy of a new Δ-1Δ system of VO

High-resolution spectra of VO have been reinvestigated in the 12 000-31 000 cm⁻¹ region. VO was produced in a vanadium hollow cathode lamp by discharging 1.5 Torr of Ar and the spectra were recorded using a Fourier transform spectrometer. The oxygen needed to produce VO was present in the system as an impurity. Three new bands observed in the 21 000-22 100 cm⁻¹ region have been attributed to a new ²Δ-1²Δ electronic transition of VO. Two bands, with origins near 21 044 and 22 038 cm⁻¹, have been assigned as the 0-1 and 0-0 bands of the ²Δ_3/2-1²Δ_3/2 sub-band while a weak band with an origin near 21 975 cm⁻¹ has been assigned as the 0-0 band of the corresponding ²Δ_5/2-1²Δ_5/2 sub-band. A rotational analysis of these sub-bands has been obtained and spectroscopic constants have been extracted. The 1²Δ state is known from the previous analyses of the doublet transitions of VO in the near infrared. The present observation has allowed the determination of the vibrational interval ΔG_1/2 and the equilibrium rotational constants for the 1²Δ_3/2 state.     

The ν2+ν4 Band of Carbonyl Fluoride

We have measured and fitted over 600 lines in the ν₂+ν₄ combination band of COF₂. The spectrum is well reproduced by extrapolation of rotational constants from the ν₂ and ν₄ fundamentals, with no evidence of significant perturbation. The band centre of 2195.272 15(11) cm⁻¹ permits an estimate of −11.32 cm⁻¹ for the anharmonicity constant x₂₄.     

Fourier transform spectroscopy of new emission systems of NbN in the visible region

The emission spectrum of NbN has been reinvestigated in the 8000-35 000  cm⁻¹ region using a Fourier transform spectrometer and two groups of new bands were observed. The bands observed in the 18 000-20 000 cm⁻¹ region have been assigned to a new ³Π-X³Δ transition. Three bands with R heads near 19 463.8, 19 659.0 and 19 757.0 cm⁻¹ have been assigned as 0-0 bands of the ³Π₂-X³Δ₃, ³Π₁-X³Δ₂ and ³Π_0±-X³Δ₁ subbands, respectively, of this new transition. Three additional ΔΩ = 0 bands have been observed in the 24 000-26 000  cm⁻¹ region. A 0-0 band with an R head near 25 409.9 cm⁻¹ has been assigned as a ΔΩ = 0 transition having X³Δ₂ as its lower state while two additional bands with heads near 25 518.7 and 25 534.8 cm⁻¹ were found to be ΔΩ = 0 bands having X³Δ₁ as the common lower state. Two of these three bands are perhaps subbands of a ³Δ-X³Δ transition. Most of the excited levels are affected by perturbations.     

Quantitative measurement of integrated band intensities of benzene vapor in the mid-infrared at 278, 298, and 323 K

Pressure broadened (1 atm. N₂) laboratory spectra of benzene vapor (in natural abundance) were recorded at 278, 298, and 323 K, covering 600-6500 cm⁻¹. The spectra were recorded at a resolution of 0.112 cm⁻¹ using a commercial Fourier transform spectrometer. The pressure of each benzene vapor sample was measured using high-precision capacitance manometers, and a minimum of nine sample pressures were recorded for each temperature. The samples were introduced into a temperature-stabilized static cell (19.94(1) cm pathlength) that was hard-mounted into the spectrometer. From these data a fit composite spectrum was calculated for each temperature. The number density for the three composite spectra was normalized to 296 K. The spectra give the absorption coefficient (cm² molecule⁻¹, naperian units) as a function of wavenumber. From these spectra integrated band intensities (cm molecule⁻¹ and atm⁻¹ cm⁻²) for intervals corresponding to the stronger benzene bands were calculated and were compared with previously reported values. We discuss and quantify error sources and estimate our systematic (NIST Type-B) errors to be 3% for the stronger bands. The measured absorption coefficients and integrated band intensities are useful for remote sensing applications such as measurements of planetary atmospheres and assessment of the environmental impact of terrestrial oil fire emissions.     

SERS investigation of interfacial water at a silver electrode in acetonitrile solutions

Surface-enhanced Raman scattering from a silver electrode in solution of 0.1 M LiClO₄ in acetonitrile has been analyzed as a function of applied potential. Three ν(O-H) bands associated with the interfacial water and two ν(O-H) bands associated with the OH⁻ ion species were observed depending on the electrode potential. The band at 3487 cm⁻¹ is favored at relatively positive potentials and assigned to H₂O molecules interacting with the electrode surface via the oxygen atoms. Another band at 3586 cm⁻¹ appears in a wider potential region and is assigned to the H₂O molecules with one or both of the hydrogen atoms facing the electrode surface. Additionally, evidence for the possible surface ion pair, Li⁺OH⁻, which is closely associated with H₂O molecules and the quasi-crystalline form of LiOH are also presented in this paper.     

Vibrational Spectroscopy of the Borate Mineral Priceite—Implications for the Molecular Structure

ABSTRACT

Priceite is a calcium borate mineral and occurs as white crystals in the monoclinic pyramidal crystal system. We have used a combination of Raman spectroscopy with complimentary infrared spectroscopy and scanning electron microscopy with Energy-dispersive X-ray Spectroscopy (EDS) to study the mineral priceite. Chemical analysis shows a pure phase consisting of B and Ca only. Raman bands at 956, 974, 991, and 1019 cm^?1 are assigned to the BO stretching vibration of the B₁₀O₁₉ units. Raman bands at 1071, 1100, 1127, 1169, and 1211 cm^?1 are attributed to the BOH in-plane bending modes. The intense infrared band at 805 cm^?1 is assigned to the trigonal borate stretching modes. The Raman band at 674 cm^?1 together with bands at 689, 697, 736, and 602 cm^?1 are assigned to the trigonal and tetrahedral borate bending modes. Raman spectroscopy in the hydroxyl stretching region shows a series of bands with intense Raman band at 3555 cm^?1 with a distinct shoulder at 3568 cm^?1. Other bands in this spectral region are found at 3221, 3385, 3404, 3496, and 3510 cm^?1. All of these bands are assigned to water stretching vibrations. The observation of multiple bands supports the concept of water being in different molecular environments in the structure of priceite. The molecular structure of a natural priceite has been assessed using vibrational spectroscopy.     

Fourier transform emission spectroscopy and ab initio calculations on NbCl

The emission spectrum of NbCl has been recorded in the 3000-20 000 cm⁻¹ region using a Fourier transform spectrometer. The bands were observed by microwave excitation of a mixture of NbCl₅ vapor and He. Two groups of bands observed in the 6500-7000 cm⁻¹ and 9800-11 000 cm⁻¹ regions have been assigned to two electronic transitions. Five bands observed in the 6500-7000 cm⁻¹ region consist of R, P, and Q branches with no combination defect or Λ-doubling. They have been assigned as five sub-bands of a ΔΛ=±1 transition with Λ>1. Nine bands observed in the 9800-11 000 cm⁻¹ regions consist of R and P branches, and they are also free from Λ-doubling. These bands have been classified into four sub-bands of a ΔΛ=0 transition (with Λ>1), which has tentatively been assigned as . The two transitions have no electronic states in common. Ab initio calculations have been performed on NbCl and the spectroscopic properties of the low-lying electronic states have been calculated. The ground state of NbCl has been predicted to be a state arising from the 3σ¹ 1δ² 2π¹ configuration, with a low-lying state at 1300 cm⁻¹ from the 3σ¹ 1δ¹ 2π² configuration. The results of our experimental and theoretical studies will be presented. This work represents the first experimental investigation of the spectra of NbCl and the first ab initio prediction of the spectroscopic properties of the low-lying electronic states.     

Observation of hot bands in the infrared spectrum of H2CO

Two hot bands in the infrared spectrum of formaldehyde (H₂CO) have been identified by means of tunable infrared laser spectroscopy using a jet-cooled sample. One band falls in the region 2760-2800 cm⁻¹; it follows a-type selection rules and it has been assigned as the ν₁ + ν₄ − ν₄ hot band. The other band falls in the region 2800-2860 cm⁻¹; it follows b-type selection rules and it has been assigned as the ν₅ + ν₄ − ν₄ hot band. The observations are restricted to low J and K_a levels. It has consequently been possible to ignore the effects of the extensive Coriolis couplings involving these levels in the analysis of the spectra and to model the rotational structure as that of a simple asymmetric top. Least-squares fits of the data have provided values for the band origins: 2774.2706(11) cm⁻¹ for the ν₁ + ν₄ − ν₄ and 2829.2621(8) cm⁻¹ for the ν₅ + ν₄ − ν₄ band. Term values for the upper vibrational levels involved in the transitions have been determined by use of the previously reported term values for the v₄ = 1 level.     

Fourier transform spectroscopy of N2O weak overtone transitions in the 1-2 μm region

The absorption spectrum of the natural sample of nitrous oxide has been recorded at Doppler limited resolution with a Fourier-transform spectrometer in the spectral range 5000-10 000 cm⁻¹. Ten cold bands (8Σ − Σ and 2Σ − Π), thirteen hot bands (11Π − Π, Σ − Σ, and Δ − Δ) of ¹⁴N₂¹⁶O and the 3ν₃ band of ¹⁴N¹⁵N¹⁶O have been newly detected. The uncertainty of the line position determination is estimated to be about 0.005 cm⁻¹ for unblended lines. The assignment of the spectrum has been done with the help of the prediction performed within the framework of the polyad model of effective Hamiltonian. The spectroscopic parameters G_v, B_v, D_v, H_v, and q_v have been determined for all newly detected bands. The line intensities of 13 weak bands have been measured. The uncertainty of the obtained line intensity values varies from 7 to 13%.     

Laser diode photoacoustic and FTIR laser spectroscopy of formaldehyde in the 2.3 μm and 3.5 μm spectral range

The room temperature operating GaInAsSb/AlGaAsSb based diode laser and 66 K InAsSb/InAsSbP laser diode both operating in spectral range of formaldehyde absorption 4350-4361 cm⁻¹ and 2821-2823 cm⁻¹ have been characterized and compared. Very precise arrangement of laser absorption together with high resolution Fourier transform technique was tested. The photoacoustic technique was employed to determine the detection limit of formaldehyde (less than 1 ppmV) diluted by nitrogen for the strongest absorption line of the ν₃ + ν₅ band in the emission region of the GaInAsSb/AlGaAsSb diode laser. The detection limit (less than 10 ppbV) of formaldehyde was achieved in the 2820 cm⁻¹ spectral range in case of InAsSb/InAsSbP laser (fundamental bands of ν₁, ν₅)_.     

Vibrational assignment of isoxazole aided by rovibrational data and density functional theory

IR and Raman spectra of isoxazole and D₃-isoxazole are reassigned with the aid of density functional theory calculations at the B3LYP/6-311+G(d,p) level. Harmonic wavenumber values of all non-CH stretch modes give an r.m.s. deviation from experimental values of 3 cm⁻¹ when they are uniformly scaled by 0.9818. Anharmonic values obtained using a second-order perturbative approach show an r.m.s. deviation of 7.6 cm⁻¹. Results of equal quality are obtained for D₃-isoxazole. Predicted Raman and IR band strengths match experimental spectra very closely. Detailed re-examination of rovibrational constants and inertial defect data from high resolution IR spectra, in comparison with values from the anharmonic frequency calculation, provides confirmation of the vibrational assignments. ‘Dark state’ fundamentals ν₁₂ (900.2 cm⁻¹) and ν₁₅ (866 cm⁻¹) are detected through the perturbations they cause in nearby bands.     

Global modeling of CO2 absolute line intensities from CW-CRDS and FTS measurements in the 1.6 and 2.0 μm regions

Line intensities of ¹³C¹⁶O₂ have been measured between 5851 and 6580 cm⁻¹ using CW-cavity ring down spectroscopy (CRDS) and in the 4700-5050 and 6050-6850 cm⁻¹ regions using Fourier transform spectroscopy. As a result of the high sensitivity (noise equivalent absorption α_min∼3×10⁻¹⁰ cm⁻¹) and high dynamics allowed by CW-CRDS, accurate line intensities of 2039 transitions ranging between 1.1×10⁻²⁸ and 1.3×10⁻²³ cm⁻¹/(molecule cm⁻²) were measured with an average accuracy of 4%. These transitions belong to a total of 48 bands corresponding to the ΔP=9 series of transitions. Additionally, unapodized absorption spectra of ¹³C-enriched samples have been recorded using a high-resolution Bruker IFS125HR Fourier transform spectrometer. Spectral resolutions of 0.004 cm⁻¹ (maximum optical path difference (MOPD)=225 cm) and 0.007 cm⁻¹ (MOPD=128.6 cm), and pressure×path length products in the ranges 5.2-12 and 69-450 hPa×m have been used for the lower and higher energy spectral regions, respectively. Absolute line intensities have been measured in the 2001i−00001, 3001i−00001 (i=1, 2, 3) and 00031−00001 bands. An excellent agreement was achieved for the line intensities of the 3001i−00001 (i=1, 2, 3) bands measured by both FTS and CW-CRDS. The CW-CRDS and FTS experimental intensity data together with selected intensity information from the literature have been fitted simultaneously using the effective operators approach. Two sets of effective dipole moment parameters have thus been obtained, which reproduce the observed line intensities in the 2.0 and 1.6 μm regions within experimental uncertainties.     

Near-infrared spectroscopy of palladium-containing layered double hydroxides used as catalysts

Three catalysts consisting of layered double hydroxides (LDHs) of magnesium and aluminum, and containing palladium in various forms, were synthesized and subsequently characterized by mid- and near-infrared spectroscopies. The results thus obtained are compared with those for a pure Mg/Al layered double hydroxide. The spectra for the Pd-containing LDHs (particularly the strength of the bands) were found to depend on the particular palladium form present. As a rule, the mid-infrared spectra contained a strong, broad band at 3800-2500 cm⁻¹ due to stretching vibrations of the different types of hydroxyl groups present in the solids and another signal at ca. 1370 cm⁻¹ due to the presence of carbonate ions in the interlayer region. These signals were the strongest in the near-infrared spectra, which were also quite similar, roughly, for all solids.     

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.     

High-Resolution Infrared Studies of ν1, 2ν1, and 2ν4 Bands of CHCl3

The C-H stretching fundamental band ν₁ (3033 cm⁻¹) of chloroform CH³⁵Cl₃ has been investigated together with the first overtone 2ν₁ (5941 cm⁻¹) in order to determine the rotation vibration parameters. From the ν₁ band α₁^C=−0.025 46(41)×10⁻³ cm⁻¹ and α₁^B=−0.010 688(44)×10⁻³ cm⁻¹ were obtained. The hot bands connected to the low lying fundamentals ν₃ and ν₆ have been analyzed and anharmonicity constants have been derived. Both the parallel and the perpendicular component band of the C-H bending overtone 2ν₄ have also been studied. In the parallel band (2410 cm⁻¹) more than 900 lines were included in the fit. In the perpendicular band (2443 cm⁻¹) 2615 lines were fitted using a model with one resonance. Among other things the results C₀−C_v=0.025 262 (20)×10⁻³ cm⁻¹, B₀−B_v=0.134 883 (25)×10⁻³ cm⁻¹, and (Cζ)_v=−0.111 867 56 (30) cm⁻¹ were obtained.     

Fourier transform emission spectroscopy of the CΔ-XΦ, DΔ-XΦ, GΦ-XΦ and GΦ-CΔ systems of CoCl

The emission spectrum of CoCl has been recorded in the 2000-23 000 cm⁻¹ region at high resolution. CoCl was made in a carbon tube furnace by heating cobalt metal to a temperature of about 2300 °C as well as in a DC discharge source and the spectra were observed using a Fourier transform spectrometer. The bands observed in the 2000-13 000 cm⁻¹ interval have been classified into four transitions: C³Δ-X³Φ (2500-3600 cm⁻¹), D³Δ-X³Φ (9300-10 030 cm⁻¹), G³Φ-X³Φ (8500-13 000 cm⁻¹) and G³Φ-C³Δ (7400-7900 cm⁻¹) analogous to the near infrared transitions of CoF reported previously [R.S. Ram, P.F. Bernath, S.P. Davis, J. Chem. Phys. 104 (1996) 6949.]. A rotational analysis of a number of vibrational bands of these transitions has been obtained and spectroscopic constants extracted for the low-lying electronic states of CoCl. It is found that the energy levels of CoCl correlate very well with those of CoF and CoH.     

The application of Raman and anti-stokes Raman spectroscopy for in situ monitoring of structural changes in laser irradiated titanium dioxide materials

The use of Raman and anti-stokes Raman spectroscopy to investigate the effect of exposure to high power laser radiation on the crystalline phases of TiO₂ has been investigated. Measurement of the changes, over several time integrals, in the Raman and anti-stokes Raman of TiO₂ spectra with exposure to laser radiation is reported. Raman and anti-stokes Raman provide detail on both the structure and the kinetic process of changes in crystalline phases in the titania material. The effect of laser exposure resulted in the generation of increasing amounts of the rutile crystalline phase from the anatase crystalline phase during exposure. The Raman spectra displayed bands at 144 cm⁻¹ (A1g), 197 cm⁻¹ (Eg), 398 cm⁻¹ (B1g), 515 cm⁻¹ (A1g), and 640 cm⁻¹ (Eg) assigned to anatase which were replaced by bands at 143 cm⁻¹ (B1g), 235 cm⁻¹ (2 phonon process), 448 cm⁻¹ (Eg) and 612 cm⁻¹ (A1g) which were assigned to rutile. This indicated that laser irradiation of TiO₂ changes the crystalline phase from anatase to rutile. Raman and anti-stokes Raman are highly sensitive to the crystalline forms of TiO₂ and allow characterisation of the effect of laser irradiation upon TiO₂. This technique would also be applicable as an in situ method for monitoring changes during the laser irradiation process.     

High-resolution infrared measurements on HSOH: Analysis of the OH fundamental vibrational mode

High-resolution infrared measurements of the OH-stretching mode of oxadisulfane, HSOH, at 3625 cm⁻¹ have been recorded using a Bruker IFS 120 HR Fourier transform spectrometer. More than 1300 lines have been assigned to the ν(OH) fundamental vibration mode, which is a hybrid band showing a c-type perpendicular band and an a-type parallel band spectrum of an asymmetric rotor molecule. The splitting due to the torsional-tunneling has not been observed in this band. The band center position at 3625.59260(20) cm⁻¹ as well as rotational and centrifugal distortion constants for the ν(OH) vibrational excited state have been obtained from a least-squares fit analysis of a semirigid rotor. In addition the α_OH experimental vibration-rotation correction terms of the OH-stretching mode have been derived and compared to values used in an earlier semi-empirical calculation of the HSOH structure. All data are in very good agreement with high level ab initio calculations and confirm the assignment of an earlier matrix isolation spectrum at 3608 cm⁻¹ to the ν(OH) fundamental mode.     

Infrared spectroscopy on size-controlled synthesized Pt-based nano-catalysts

Pt, Ru and Pt/Ru nano-particles, synthesized in ethylene glycol solutions, are studied using infrared (IR) spectroscopy and high resolution transmission electron microscopy (HRTEM). The synthesis method allows the control of the mono- and bi-metallic catalyst particle sizes between 1 and 5.5 nm. The IR spectra of CO adsorbed (CO_ads) on the Pt, Ru and bi-metallic Pt/Ru colloids are recorded as a function of the particle size. The stretching frequency of CO_ads depends on the particle size and composition. Strong IR bands due to the stretching vibration of CO_ads are observed between 2010 and 2050 cm⁻¹ for the Pt nano-particles, while two IR bands between 2030 and 2060 cm⁻¹ for linear bonded CO_ads, and at lower wavenumbers between 1950 and 1980 cm⁻¹ for bridged bonded CO_ads, are found for the Ru particles. The IR spectra for the Pt/Ru nano-sized catalyst particles show complex behaviour. For the larger particles (>2 ± 0.5 nm), two IR bands representative of CO_ads on Ru and Pt-Ru alloy phases, are observed in the range of 1970-2050 cm⁻¹. A decrease in the particle size results in the appearance of a third band at ∼2020 cm⁻¹, indicative of CO_ads on Pt. The relative intensity of the band for CO_ads on the Pt-Ru alloy vs. the Pt phase decreases with decreasing particle size. These results suggest that Ru is partially dissolved in the Pt lattice for the larger Pt/Ru nano-particles and that a separate Ru phase is also present. A Pt-Ru alloy and Ru phase is observed for all Pt/Ru particles prepared in this work. However, a decrease in particle size results in a decrease of the number of Pt and Ru atoms in the Pt-Ru alloy phase, as they are increasingly present as single Pt and Ru phases.