Overtone Region Research Articles

In Situ Vibrational Spectroscopy Studies of Supported Niobium Oxide Catalysts

The IR spectra of bulk Nb2O5·nH2O and niobia supported on SiO2, Al2O3, ZrO2, and TiO2 were recorded in the fundamental and overtone NbO regions, as well as in the hydroxyl region, to develop a better understanding of the structural models of surface NbOx species. The coincidence of the IR and Raman fundamental NbO frequency in Nb2O5/Al2O3, Nb2O5/ZrO2, and Nb2O5/TiO2 provides the strongest evidence that the NbOx surface species (NbO fundamental at 980 cm-1) is present as a mono-oxo moiety. The IR and Raman band positions would not be coincident for a di-oxo species. This conclusion is further supported by the presence of only a single overtone at ∼1960 cm-1 (2 × 980 cm-1) in Nb2O5/ZrO2 and Nb2O5/TiO2 and the presence of the most intense overtone at 1966 cm-1 in Nb2O5/Al2O3. Lower frequency IR fundamentals at 880 cm-1 (low loading) and 935 cm-1 (high loading) are also seen in Nb2O5/ZrO2, and the IR overtone region of Nb2O5/Al2O3 exhibited weak bands at ∼1870 cm-1 (935 cm-1 overtone) and 1914 cm-1 (935 + 980...

Intermolecular interactions in the ε phase of solid oxygen studied by infrared spectroscopy

The infrared spectra of solid oxygen, in the overtone region, have been measured in the δ and in the ε phases at low and room temperature up to 60 GPa. The two structured bands observed in the ε phase are assigned to the combination of the infrared active mode with itself and with the Raman active mode, respectively. Performing a deconvolution of the spectral profile the densities of states of the infrared and Raman active vibrational modes are obtained.

Collision-induced vibration–rotation fluorescence spectra and rovibrational symmetry changes in acetylene

The laser-induced fluorescence method has been used to investigate collision-induced processes in the hydrogen-stretching vibrational overtone region of the ground electronic state of acetylene. The fluorescence signal has been dispersed by a high-resolution interferometer. Collision-induced rovibrational symmetry changes have been observed in the spectra.

Evidence of very strong [2×ν(NO)] overtones when adsorbing NO in CuI,II-exchanged Y zeolites

In this communication the first vibrational results obtained in transmission mode, concerning NO/Cu-Y systems, containing Cu' and Cu I ions, are presented. The IR spectra of these systems are characterized by strong and well defined IR peaks, both in the v(NO) and 2 x v(NO) stretching regions. Plausible physical reasons justifying the unusual and astonishing high intensity of the peaks in the 2 x v(NO) overtone region are discussed.

Eigenstate resolved infrared and millimeter-wave–infrared double resonance spectroscopy of methylamine in the N–H stretch first overtone region

The eigenstate resolved, near-infrared spectrum of methylamine, CH3NH2, has been measured at 5 MHz resolution in the region near 6615 cm-1 using a molecular-beam laser spectrometer with optothermal detection. Part of the spectrum of the NH 2ν1 (symmetric stretch first overtone) has been assigned by applying a millimeter-wave–infrared double resonance technique. The spectra are very fractionated by intramolecular vibrational energy redistribution with an observed density of states between 20 and 30 states per cm-1 which is about four times the density of vibrational states calculated in the harmonic approximation. The coupling between the bright states and the bath is found to be rather strong (0.1 cm-1), and the lifetime for the redistribution is determined to be 3 ps for the 2ν1 vibration.

High-Resolution Study of the First Stretching Overtones of H3Si79Br

The Fourier transform infrared spectrum of monoisotopic H3Si79Br (resolution 7.7 × 10−3cm−1) was studied from 4200 to 4520 cm−1, in the region of the first overtones of the Si–H stretching vibration. The investigation of the spectrum revealed the presence of two band systems, the first consisting of one parallel (ν0= 4340.2002 cm−1) and one perpendicular (ν0= 4342.1432 cm−1) strong component, and the second of one parallel (ν0= 4405.789 cm−1) and one perpendicular (ν0= 4416.233 cm−1) weak component. The rovibrational analysis shows strong local perturbations for both strong and weak systems. Seven hundred eighty-one nonzero-weighted transitions belonging to the strong system [the (200) manifold in the local mode picture] were fitted to a simple model involving a perpendicular component interacting by a weak Coriolis resonance with a parallel component. The most severely perturbed transitions (whose ‖obs–calc‖ values exceeded 3 × 10−3cm−1) were given zero weights. The standard deviations of the fit were 1.0 × 10−3and 0.69 × 10−3cm−1for the parallel and the perpendicular components, respectively. The weak band system, severely perturbed by many “dark” perturbers, was fitted to a model involving one parallel and one perpendicular band, connected by a Coriolis-type resonance. The K" · ΔK = +10 to +18 subbands of the perpendicular component, which showed very high observed − calculated values (∼0.5 cm−1), were excluded from this calculation. The standard deviations of the fit were 11 × 10−3and 13 × 10−3cm−1for the parallel and the perpendicular components, respectively.

Infrared spectroscopy and time-resolved dynamics of the ortho-H2–OH entrance channel complex

The rotationally resolved infrared spectrum of the prereactive o-H2–OH complex in its ground electronic state is obtained in the OH overtone region at ∼1.4 μm using an IR-UV double resonance fluorescence enhancement technique. The pure OH overtone band of o-H2–OH is observed as well as approximately 20 additional rovibrational transitions extending out to the OH (X 2Π,v=2)+o-H2(X 1Σg+) dissociation limit. These transitions are assigned as combination bands involving the simultaneous excitation of the OH vibrational overtone and intermolecular bending (internal rotor) states. The assignment of the experimental spectrum is aided by a detailed comparison with the bound states computed for the ab initio potential of Clary, Werner, and co-workers [Mol. Phys. 83, 405 (1994)]. The infrared spectroscopy results also verify the topology of this ab initio potential in the entrance channel to the OH+H2 hydrogen abstraction reaction. Direct time-resolved experiments indicate that the lifetime of the vibrationally activated o-H2–OH complex in the ground intermolecular state is 115(26) ns. The initial excitation is found to stay localized in the OH intramolecular stretching mode for a long period of time prior to vibrational predissociation or chemical reaction.

Vibrational Overtone Spectroscopy of Cycloheptatriene Chromium Tricarbonyl, Benzene Chromium Tricarbonyl, and Corresponding Hydrocarbon Ligands

The vibrational overtone spectra of gaseous cycloheptatriene chromium tricarbonyl (CHTCT) and benzene chromium tricarbonyl (BCT) were recorded at the third overtone region using photoacoustic spectroscopy and compared to the spectra of the nonbonded ligands, cycloheptatriene (CHT) and benzene. Analysis of the spectra leads to the conclusion that the metal−ligand bonding lengthens the CH bond by 0.007 Å in the cycloheptatriene complex and by 0.003 Å in the benzene complex. The spectrum of BCT exhibits an additional transition which is absent in the spectrum of free benzene. The experimental peaks are assigned to the pure CH overtones and combination bands. The structural information obtained from the spectra is discussed and compared to the results of gas-phase electron diffraction and microwave spectroscopic studies. Analysis of experimental data indicates that μ6-bonding is more favorable for cycloheptatriene chromium tricarbonyl.

Vibrational Overtone Spectroscopy of Cycloheptatriene-d6 at the Third and Fourth Overtone Regions

In a previous report1 the vibrational overtone spectrum of gaseous cycloheptatriene (CHT) was presented. The main absorption features at the third and fourth overtones were assigned to the CH olefinic oscillators of CHT using a direct correlation method. Assignments were also suggested for the methylenic CH absorptions; however, further confirmation of these spectral assignments was required. In CHT-d6 the CH olefinic transitions are eliminated, and only features due to the methylenic group of the CHT ring will remain in the spectrum. The CHT-d6 was synthesized by refluxing 12 mL of C6D6 (99.6 atom % d, Aldrich) in the presence of CuBr for 3.5 h with dropwise addition of 40 mL of diazomethane (CH2N2) solution in C6D6 as was described by Muler et al.2 The diazomethane solution was generated from nitrosomethylurea according to the procedure proposed by Arndt.3 Nitrosomethylurea was prepared from acetamide and bromine as was recommended by Amstutz and Myers.4 The resulting reaction mixture contained about 2.4% CHT-d6 dissolved in the deuterated benzene. The 1H NMR of the mixture displayed the single broad peak around 2.1 ppm corresponding to the CH2 group of the CHT-d6. The amount of solvent was reduced using rotatory evaporation to bring the CHT-d6 content to 43%. Then the CHT-d6 sample (91%) was collected using preparative gas chromatography. The third and fourth overtone spectra of CHT-d6 were obtained using the photoacoustic spectrometer described previously.1 The sample pressure was 14 Torr, and 300 Torr of argon was added to increase the photoacoustic signal. The spectra of CHT-d6 and CHT at the third and fourth overtone regions are shown in Figures 1 and 2, respectively. Peak positions and vibrational assignments are tabulated in Table 1. At the third overtone the absence of the olefinic CH bond stretch absorptions in the CHT-d6 spectrum around 11 30011 400 cm-1 leaves only two well-resolved peaks associated with the methylenic CH bonds of the CHT-d6 ring (Figure 1). Based on the general pattern reported for the CH methylenic bond in cyclic hydrocarbons5 (rCHax > rCHeq) and ab initio geometry optimization for CHT,1 the lower energy peak at 11 096 cm-1 can be assigned to the CHax of CHT-d6, while the higher energy transition, located at 11 215 cm-1, belongs to the CHeq. Similar arguments can be made for the two peaks recorded in the next overtone region (Figure 2), where the CHax peak appeared at 13 643 cm-1 and the CHeq transition appeared at 13 785 cm-1. Thus, the spectral results for CHT-d6 confirmed the assignments suggested for the CHT third and fourth overtone methylenic peaks. Acknowledgment. The authors wish to thank Dr. Thomas Kinstle for assistance in the synthetic part of work and J. Romanowitz for the GCMS analysis of the samples.

Determination of free fatty acids in palm oil by near‐infrared reflectance spectroscopy

AbstractA near‐infrared (NIR) spectroscopy calibration was developed for the determination of free fatty acids (FFA) in crude palm oil and its fractions based on the NIR reflectance approach. A range of FFA concentrations was prepared by hydrolyzing oil with 0.15% (w/w) lipase in an incubator at 60°C (200 rpm). Sample preparation was performed in Dutch cup, and the spectra were measured in duplicate for each sample. The optimized calibration models were constructed with multiple linear regression analysis based on C=O overtone regions from 1850–2050 nm. The best wavelength combinations were 1882, 2010, and 2040 nm. Multiple correlation coefficients squared (R2) were: 0.994 for crude palm oil, 0.961 for refined‐bleached‐deodorized (RBD) palm olein, and 0.971 for RBD palm oil. Calibrations were validated with an independent set of 8–10 samples. R2 of validation were 0.997, 0.943, and 0.945, respectively. The developed method was rapid, with a total analysis time of 5 min, and environmentally friendly, and its accuracy was generally good for raw‐material quality control.

New Infrared Transitions in Solid Parahydrogen in the MIR and NIR/VIS Regions

We have studied the infrared spectrum of solid parahydrogen at different orthohydrogen impurity levels in the mid-infrared (MIR) region between 600–2000 cm−1and in the near infrared/visible (NIR/VIS) region between 10000–16500 cm−1. The most important new observations in the MIR region, obtained with a single pass through an absorption cell 4.75 cm in length, are the U0(0) +S0(0) double transition around 1520 cm−1, broadened to about 20 cm−1by roton delocalization, and the single orthohydrogen transition U0(1) at 1619.12 cm−1, which was previously observed only in normal hydrogen. For the NIR/VIS measurements an internal multireflection cell with 14-cm absorption path length was used. Of particular interest here is the second overtone band of solid hydrogen including double transitions of the type Q2(J) + Q1(J′) (J= 0, 1;J′ = 0, 1). At 10241.07 cm−1the new single transition W2(0) could be observed. For several double transitions in the NIR/VIS region a fine structure is observed, which can be explained by anisotropic interaction in rotationally excited pairs of molecules. The treatment of the fine structure of the Q2(0) + S1(0) transition leads to the prediction of a considerable intensity of the triple transition Q2(0) + Q1(0) + S0(0). Stimulated by this result we have found the triple transitions Q1(0) + Q1(0) + S0(0) at 8660 cm−1and S1(0) + Q1(0) + S0(0) at 8990 cm−1in the first overtone region. At 12788 cm−1we detected an absorption feature that we have assigned to the triple transition S1(0) + Q1(0) + Q1(0). We explain the infrared activity of this transition in terms of a three-body process, a dipole moment induced within a triplet of hydrogen molecules by successive pairwise induction.

Λ-Splittings and Line Intensities in the 3 ← 1 Hot Band of14N16O: The Spectrum of Nitric Oxide in the First Overtone Region

Intensities and Λ-splittings have been measured for lines belonging to the 3 ← 1 hot band of14N16O. The vibrational transition moment and the Herman–Wallis coefficient have been determined. Hamiltonian constants have been calculated for the four vibrational statesv= 0, 1, 2, and 3, and a synthetic spectrum has been generated in the first overtone region of NO, taking into account the hyperfine structure for the 2 ← 0 band.

IR-induced interconversions between five conformers of methanol dimers trapped in nitrogen matrix

Interconversions between five open-chain conformers of methanol dimer trapped in solid nitrogen have been studied through selective excitation of their CH and OH stretching modes. A nearly complete vibrational assignment for three of them is deduced from these irradiation effects and also from thermal conversion observed between 7 and 8 K. Kinetic studies allow us to precise the schemes of conversion and, in favourable cases, to get the quantum yields which are significantly mode dependent. A careful examination of the CO stretching overtone region, around 2050 cm −1, led to the identification of a simultaneous transition of the CO stretching mode of both molecules, with intensities strongly varying according to the conformer. Such a variation is accounted for in the framework of the theory of the intensities of combination transitions, assuming a dipole-dipole interaction between the two CO bonds.

The v1, v2, 2v3, v2 + v3 band systems and the overtone region of HCNO above 4000 cm−1: A Network of Resonance Systems

AbstractThe v2, 2v3, v1, v2 + v3, 3v3, 2v2, v1 + v3, v2, + 2v3, v1 + v2 and 2v2 + v3 band systems of HCNO could be identified between 1800 and 5800 cm−1. In addition, new transitions in the v5, v4 and v3 band systems could be assigned. The determination of spectroscopic power series coefficients shows that every assigned vibrational level is perturbed. Most of the interactions are part of resonance systems which are embedded in a grand network of interacting states. This network can be built up on the basis of the resonance systems 00010/00002, 00100/00004 and 01000/00015. In this paper the 01010/01002/00201/00113/[00025] and the 01110/01102/00301/00213/[01014]/[00125] resonance systems are presented. Vibrational quantum numbers in brackets indicate that the vibrational term value of the vibrational state is only estimated. The 10003/10011/00205 and 10005/01201 resonance systems, which do not fit into this network, are also discussed. The effect of excitation of the stretching modes v1, v2 and v3 on the v5 manifold and the quasilinear parameter y0 are examined.

Theoretical study of vibrational overtone spectroscopy and dynamics of methanol

Experimentally observed coupling between OH and CH stretching modes in the high overtone region has been modeled successfully in terms of a curvilinear internal coordinate Hamiltonian including harmonic coupling between anharmonic OH and CH stretching oscillators and cubic Fermi resonance kinetic and potential energy couplings between CH stretches and HCH bends. The Hamiltonian matrices have been set up in block diagonal forms including only resonant states. The potential-energy parameters have been optimized by the least-squares method using experimental vibrational term values as data. The OH/CH stretch interaction parameter obtained agrees well with the one calculated by perturbation theory from a published ab initio harmonic force field. The model has reproduced well experimental band origins in the OH stretching overtone region, and it has provided assignments for the bending overtones in the CH stretching fundamental region. Finally, a unitary transformation is found from the internal coordinate representation to the corresponding normal coordinate representation providing a set of normal coordinate parameters like diagonal anharmonicity parameters, Darling–Dennison resonance constants and cubic Fermi resonance force constants. The results confirm the experimental finding of energy redistribution between the OH and CH stretching modes on subnanosecond time scale at 5νOH.

High-resolution Fourier-transform spectroscopy of solid parahydrogen in the first overtone region

The first vibrational overtone spectrum of solid parahydrogen with various low orthohydrogen impurity levels has been studied in the range 7900--10 000 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ using a White-type external multireflection system with a 34.8-cm sample path length. We were able to detect extremely weak features, namely, the ${\mathrm{Y}}_{1}$(0) at 7991.85 (1) ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$, and the double transitions ${\mathrm{U}}_{1}$(0) + ${\mathrm{Q}}_{1}$(1), ${\mathrm{U}}_{1}$(0) + ${\mathrm{S}}_{1}$(0), ${\mathrm{U}}_{1}$(1) + ${\mathrm{Q}}_{1}$(0), and ${\mathrm{Q}}_{1}$(0) + ${\mathrm{Q}}_{1}$(0). The ${\mathrm{Q}}_{1}$(0) + ${\mathrm{Q}}_{1}$(1) and ${\mathrm{Q}}_{1}$(1) + ${\mathrm{Q}}_{1}$(1) double transitions were resolved. We obtained a rich orthohydrogen satellite spectrum associated with the transitions ${\mathrm{Q}}_{2}$(0) and ${\mathrm{Q}}_{2}$(1) near 8060 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$. An analysis and assignment of these satellite transitions are presented. The double transitions of the type ${\mathrm{Q}}_{1}$(J) + ${\mathrm{Q}}_{1}$(${\mathrm{J}}^{|\mathrm{I}\mathrm{H}}$) (J,${\mathrm{J}}^{|\mathrm{I}\mathrm{H}}$ = 0,1) are located in the spectral region around 8300 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$. The most remarkable features here are the ${\mathrm{Q}}_{1}$(1) + ${\mathrm{Q}}_{1}$(1) transition, which consists entirely of fine structure, and the ${\mathrm{Q}}_{1}$(0) + ${\mathrm{Q}}_{1}$(0) transition, which, to our knowledge, has an intensity that cannot be accounted for by previously proposed mechanisms. Finally the thermal shift of all of the above-mentioned transitions was investigated by lowering the sample temperature from 12.5 K down to 6.5 K while taking spectra. The influence of the change of temperature on the line positions, linewidths, and interaction parameters of solid hydrogen is discussed.

Vibrational Overtone Spectroscopy of Butadiene Iron Tricarbonyl and 1,3-Butadiene

The photoacoustic vibrational overtone spectrum of gaseous butadiene iron tricarbonyl (BDIT) at the third overtone region was recorded and compared to that of 1,3-butadiene. The effect of the metal, determined by an interpretation of the overtone spectrum of the complex, is to lengthen the terminal trans CH bond of the 1,3-butadiene ligand by 0.0024 A while the terminal cis bond does not change significantly. The assignments of the terminal cis, terminal trans, and nonterminal CH stretch overtone absorptions are supported by ab initio geometry optimization calculations of the trans and cis butadiene and the BDIT complex. The spectrum of the complex possessed three additional bands not seen in the free ligand. These bands originate from vibrational coupling induced by the presence of the metal.

Rovibrational spectroscopy of the C 2H 2Ar van der Waals complex, using a fluorescence depletion infrared-ultraviolet double resonance technique

A rovibrational spectrum of the acetylene-argon van der Waals (vdW) complex, C 2H 2Ar, has been measured in the 1.52 5 μm ‘2 ν CH’ overtone region by a time-resolved infrared-ultraviolet double resonance method. Infrared absorption by the vdW complex is recorded as a depletion of laser-induced rovibronic fluorescence intensity, providing a novel way to measure rovibrational spectra of simple vdW complexes and to study their predissociation dynamics.

Isotopically selective IR multiphoton dissociation of 1,3,5-trioxane

Searching for oxygen-isotope selectivity, we investigated the infrared multiphoton dissociation of the formaldehyde trimer around 10 µm, in a range where the molecule has a degenerate and a non-degenerate CO stretch vibration and a degenerate CH2 deformation vibration. In the region of the two latter, the wavelength dependence of the dissociation yield exhibits sharp structures. They were assigned ton-photon resonances (n = 2, 3, 5) by the help of the IR spectrum in the fundamental and overtone region. The O and C selectivities were very small (1.05) near the non-degenerate CO stretch band, but surprisingly large (2–4) in the CH2 deformation, which has no isotopic shift. The selectivity is not controlled by the first (n-photon) excitation step, but only by a later step. Its assignment is attempted. The pressure dependence of the dissociation is peculiar: Only after an initial decrease, the yield exhibits the usual rise with pressure. We attribute the decrease to a relaxation which perturbs the two-photon resonance.

Fermi resonances and local modes in stibine, SbH3: A Fourier interferometric and laser photoacoustic study of the overtone spectrum

The third stretching overtone region of a natural sample of stibine, SbH3, has been studied with high resolution infrared spectroscopy and the fifth and the sixth overtone region with Ti:Sapphire ring laser intracavity photoacoustic spectroscopy. The third overtone consists of a local mode pair of bands (400A1/E) which have been rotationally assigned both for 121SbH3 and 123SbH3 with a vibration-rotation model based on rectilinear normal coordinates. The vibrational dependencies of the model parameters are explained well with a simple block diagonal vibrational model. An extension of the standard vibration-rotation model is used to show that the upper state rotational energy level structures of both isotopic species are close to the rotational structure of an asymmetric rotor. High resolution laser spectrum of the fifth overtone consisting of a local mode pair of bands (600A1/E) shows severe perturbations in the upper state rotational structure. The (510A1/E) and (700A1/E) bands have been recorded with low resolution. All experimentally known vibration-rotation band origins of 121SbH3 have been reproduced well with a curvilinear internal valence coordinate system based Fermi resonance local mode model. The potential energy surface obtained agrees well with recent ab initio results.