Stretching Mode Ν3 Research Articles

Ro-vibrational Spectrum of Linear Dialuminum Monoxide (Al2O) at 10 μm.

Dialuminum monoxide, Al2O, has been investigated in the laboratory at mid-IR wavelengths around 10 μm at high spectral resolution. The molecule was produced by laser ablation of an aluminum target with the addition of gaseous nitrous oxide, N2O. Subsequent adiabatic cooling of the gas in a supersonic beam expansion led to rotationally cold spectra. In total, 848 ro-vibrational transitions have been assigned to the fundamental asymmetric stretching mode ν3 and to five of its hot bands, originating from excited levels of the ν1 symmetric stretching mode and the ν2 bending mode. The measurements encompass 11 vibrational energy states (v1 v2l v3). The ro-vibrational transitions show spin statistical line intensity alternation of 7:5, which is caused by two identical aluminum nuclei of spin I = 5/2 at both ends of the centrosymmetric molecule of structure Al-O-Al. The less effective cooling of vibrational states in the supersonic beam expansion allowed measurement of transitions in excited vibrational states at energies of 1000 cm-1 and higher, while rotational levels within vibrational modes exhibited thermal population, with rotational temperatures around Trot = 115 K. Molecular parameters for 11 vibrational states were derived, including rotation and centrifugal distortion constants and l-type doubling constants for the states (v1 v2l v3) = (0 11 0) and (0 11 1) and an l-type resonance between the states (0 20 0) - (0 22 0) and (0 20 1) - (0 22 1). From the experimental results, rotational correction terms and the equilibrium bond length re were derived. The measurements were supported and guided by high-level quantum-chemical calculations that agree well with the derived experimental results.

In-Situ Single Crystal XRD and Raman Spectra Investigation of (Mg, Fe, Mn)CO3 at Various Temperatures

The in-situ X-ray diffraction (XRD) and Raman spectra of synthetic (Mg, Fe, Mn)CO3 single crystals for (Mg0.37Fe0.31Mn0.32)CO3, (Mg0.49Fe0.51)CO3, (Fe0.47Mn0.53)CO3, and (Mg0.50Mn0.50)CO3 were investigated up to 871 K. Lattice parameters and the volumetric thermal expansion coefficients were achieved, demonstrating an inherent anisotropy of c/a near to 3.0. The Raman spectra of our intermediate components all exhibit a negative temperature dependence similar to that of the end members. The temperature dependence of the external modes T, L, anti-symmetric stretching mode ν3, and out-of-plane bending mode 2ν2 is generally more prominent than the in-plane bending mode ν4 and symmetric stretching mode ν1 except for siderite FeCO3. Combining thermal expansion coefficients αV with the relative changes in frequency δνi/δT of Raman spectra, the average thermodynamic Grüneisen parameters (γth) for (Mg0.37Fe0.31Mn0.32)CO3, (Fe0.47Mn0.53)CO3, (Mg0.50Mn0.50)CO3, MgCO3, and MnCO3 were obtained as 1.18, 1.36, 1.34, 1.13, and 1.53, respectively. The relationship between Fe2+ and Mn2+ contents and γth illustrates that the concentration of Fe2+ causes a negative effect while the concentration of Mn2+ causes a positive effect on γth. These results could provide a reference for the contribution of Fe2+ and Mn2+ on the structural and thermodynamic properties of (Mg, Fe, Mn)CO3 carbonates.

In Situ Raman Spectroscopic Studies of Liquid Carbon Tetrachloride (CCl4) Under Static and Laser-Driven Shock Compression.

High pressure (up to ∼2.2 GPa) Raman scattering studies were performed in carbon tetrachloride (CCl4) under static and dynamic compressions using diamond anvil cell (DAC) and laser-driven shock methods, respectively, and their results are compared. The laser-driven shock experiments were conducted in a glass-confined target geometry. The symmetric stretching mode ν1, symmetric bending mode ν2, and asymmetric bending mode ν4 blueshifts with pressure. Mode Gruneisen parameters were obtained for the above Raman modes. Time-resolved Raman spectroscopic (TRRS) studies were performed under laser-driven shock compression at different delay times. Shock velocity deduced from the intensity ratios of Raman signal scattered from unshocked and shocked regions of symmetric stretching mode is in agreement with the one obtained from one-dimensional hydrodynamic simulations.

Crystal structure, Raman spectroscopy and microwave dielectric properties of xBa3MgNb2O9–(1-x)Ba2InNbO6 [x = 0.4, 0.6, 0.8

The dependence of the microwave dielectric properties of xBa3MgNb2O9–(1-x)Ba2InNbO6 [x = 0.4, 0.6, 0.8] on the structural parameters is investigated. The solid-state reaction technique is applied to synthesize these materials and the structural parameters are obtained from the Rietveld refinement of the X-ray diffraction (XRD) data of the samples. The Rietveld refinement confirms the tetragonal crystal structure of all the samples with space group P4/mnc (D4h6). It has been observed that the Raman shift of the stretching mode ν1 (BO6) and the ionic polarizability of the cations strongly influenced the dielectric constant (εr) whereas the value of the quality factor Qf depends upon the width of ν1 (BO6) mode. It is observed that the temperature coefficient of resonant frequency (τf) increases with the increase of the octahedral-distortion in the crystal structure. The factors affecting the microwave dielectric properties are discussed based on the vibrational and structural data.

Line intensity measurements and analysis in the ν3 band of ruthenium tetroxide

Ruthenium tetroxide (RuO4) is a heavy tetrahedral molecule characterized by an unusual volatility near ambient temperature. Because of its chemical toxicity and the radiological impact of its 103Ru and 106Ru isotopologues, the possible remote sensing of this compound in the atmosphere has renewed interest in its spectroscopic properties. The present contribution is the first investigation dealing with high-resolution line-by-line intensity measurements for the strong fundamental band observed near 10 μm, associated with the excitation of the infrared active stretching mode ν3. It relies on new, high resolution FTIR spectra recorded at room temperature, using a specially constructed cell and an isotopically pure sample of 102Ru16O4. Relying on an effective Hamiltonian and associated effective dipole moment [S Reymond–Laruinaz et al, J Mol Spectrosc 2015;315:46–54], the measured line intensities were assigned and dipole moment parameters determined. A HITRAN-formatted frequency and intensity line list was generated.

Effects of Fermi resonance of ν1 and 2ν2 on the Raman scattering of fundamental mode ν2 from liquid carbon disulfide

Raman scattering from liquid carbon disulfide has been studied for different concentrations in benzene. Modes ν1 (656cm−1) and 2ν2 (796cm−1) are allowed bands of carbon disulfide, while ν2 (396cm−1) is forbidden by the selection rules. However, a weak band has been observed along with the strong allowed totally symmetrical stretching mode ν1. The observation is ascribed to the effects of the vibrational anharmonicity of free molecule and intermolecular interaction potential. The ν1 and 2ν2 Fermi resonance can be influenced by the external conditions. The effects of the ν1 and 2ν2 Fermi resonance on the Raman frequency and relative intensity are discussed and the Raman scattering cross section of ν2 is studied for different concentration of carbon disulfide in benzene. The second-order perturbation quantum theory is introduced to explain the results that the Raman scattering of ν2 is influenced by 2ν2 and its Fermi resonance with ν1.

Spectroscopic and bond-topological investigation of interstitial volatiles in beryl from Slovakia

Nine beryl samples from Western Carpathians, Slovakia, were investigated by infrared and Raman spectroscopy and differential thermal analysis. Two types of water H2O I and H2O II were detected. Infrared spectroscopy proved the presence of water type I and II in the presence of alkali cations with several bands: (1) symmetric stretching vibration—ν1; (2) antisymmetric stretching mode—ν3; (3) bending vibration—ν2. The presence of singly and doubly coordinated type II water (IIs and IId) was confirmed by single-crystal IR spectroscopy. From Raman spectra a band at 3606 cm−1 was assigned to ν1 of water type I and the range of 3597–3600 cm−1 to water type II. The presence of doubly coordinating water indicates a relatively highly hydrated environment with the presence of alkali ions including Na as the dominant cation coordinated by H2O II. CO2 bands were detected only by single-crystal IR spectroscopy. Thermal analysis proved total water loss in the range of 1.4–2.0 wt% and three main dehydration events. Based on the study of bond-topological arrangements two molecules of H2O IId are each bound with two H···O1 bonds and one Na–OW bond with an angular distortion, and by releasing one H2O molecule more stable H2O IIs is produced. The H2O I molecule is bound only by two equivalent hydrogen bonds. The H2O IIs molecule with a Na–OW bond strength of 0.28 vu and two H···O1 bonds of 0.14 vu without any forced angular distortion is the most stable of all.

Gas-Phase Spectroscopic Detection and Structural Elucidation of Carbon-Rich Group 14 Binary Clusters: Linear GeC3Ge

Guided by high-level quantum-chemical calculations at the CCSD(T) level of theory, the first polyatomic germanium-carbon cluster, linear Ge2C3, has been observed at high spectral resolution in the gas phase through its remarkably complex fundamental antisymmetric C-C stretching mode ν3 located at 1932 cm(-1). The observation of a total of six isotopic species permits the derivation of a highly accurate value for the equilibrium Ge-C bond length. The present study suggests that many more Ge-C species might be detectable in the future using a combination of laser-ablation techniques for production and high-resolution infrared and/or microwave techniques for spectroscopic detection.

μ-Raman and infrared reflectance spectroscopy characterization of (Lu1−xGdx)2SiO5 solid solution single crystals doped with Dy3+ or Sm3+

Single crystals of Lu2SiO5:5 at% Dy3+ - LSO:5Dy,(Lu0.6Gd0.4)2SiO5:4 at% Dy3+ - 60LGSO:4Dy and (Lu0.4Gd0.6)2SiO5:5 at% Sm3+ - 40LGSO:5Sm were obtained by the Czochralski method. It was found that the crystallographic structure of investigated crystals is isostructural with Lu2SiO5 which crystallizes in monoclinic system within a space group C2/c. Detailed spectroscopic analysis in a wide spectral region was carried out for these three solid solution crystals using two complementary techniques polarized Raman and infrared reflectance spectroscopy. Additional interesting information for the low-wavenumber range phonons were obtained using an NExT filter. The red shift of almost all modes with increasing gadolinium content was observed. It results from an increase in the lattice constants. The change in the splitting of the most intense symmetric stretching mode ν1 assigned to vibrations of SiO4 tetrahedra was observed with increasing gadolinium content. The spectral distance between the two components of this mode decreased from 23 cm−1 for LSO:5Dy through 20 cm−1 for 60LGSO:4Dy to 14 cm−1 for 40LGSO:5Sm. Analysis of vibrational spectra provides the information about structural changes and increase in crystal structure disorder with increasing gadolinium content. Increasing disorder observed in vibrational spectra indicates the possibility of substantial broadening of spectral lines of optically active ions in luminescence spectra.

An ASAP treatment of vibrationally excited S2O: The ν3 mode and the ν3 + ν2 − ν2 hot band

The fundamental S–S stretching mode ν3 of disulfur monoxide, S2O, located at 679cm−1, has been investigated using Fourier-transform far-infrared spectroscopy at the SOLEIL synchrotron facility. A spectroscopic analysis has been performed using an Automated Spectral Assignment Procedure (ASAP) which permits accurate determination of more than 2000 energy levels from ν3. In addition, the ν3+ν2−ν2 hot band was observed for the first time and some 500 corresponding energy levels were assigned. The high-resolution synchrotron study was complemented with pure rotational spectra of S2O in the (v1,v2,v3)=(0,0,1) vibrational state observed in the frequency range from 250 to 280GHz using a long-path absorption cell. From these combined measurements, extensive molecular parameter sets have been determined and precise band centers have been derived for both vibrational bands.

Vibrational assignment and vibronic interaction for NO3 in the ground electronic state

Two important problems exist for the NO3 free radical. One is the frequency of the degenerate N–O stretching mode ν3. It has been assigned to a band at 1492cm−1 (Assignment I), whereas Stanton calculated it by an ab initio MO method to be around 1000cm−1 (Assignment II). The second concerns an anomalous ν4 progression, which appeared in the photoelectron spectra of the NO3 anion and was accounted for by Herzberg–Teller (H–T) mechanism, but the interaction parameter derived was too large. The present study critically examines Assignment II and the H–T vibronic interaction model against the results of high-resolution infrared (IR) spectroscopy supplemented with dispersed fluorescence (DF), and concludes Assignment I to be correct and the H–T mechanism to be complemented by a new vibronic interaction model, based upon the observations: (1) Stanton’s ab initio MO ν3 appeared in neither IR nor DF spectra, (2) only one A–E type subband was present in the Z−ν4 hot band (Z denotes the upper state of the 1492cm−1 band), at variance with the two predicted by Assignment II, (3) the ℓ-type doubling constant and the first-order Coriolis coupling constant derived for the Z state by assuming Assignment II were not acceptable, and (4) anomalous features expected from the H–T vibronic interaction model for the ν4 fundamental state were not observed at all. Infrared spectroscopic results on a few 2E′ degenerate states indicated that the first-order Coriolis coupling constant and the effective spin–orbit interaction constant were closely correlated, suggesting that the unpaired electron azimuthal motion was affected much by that of the degenerate vibrational mode. This sort of vibronic interaction has been well known for linear polyatomic free radicals in 2Σ electronic states with a bending mode singly excited. A similar vibronic interaction should be present also in symmetric-top free radicals, where a degenerate vibrational mode is singly excited. However, few examples have been reported and the NO3 radical is perhaps the first case, where the unpaired electron was shown to be strongly coupled with an excited degenerate vibrational mode, as was evidenced in the observed IR and DF spectra.

Ultrafast vibrational dynamics of BH4(-) ions in liquid and crystalline environments.

Ultrafast vibrational dynamics of BH4(-) ions, the key units in boron hydride materials for hydrogen storage, are studied in diluted polar liquid solution and in NaBH4 crystallites by femtosecond infrared spectroscopy. Two-color pump-probe experiments reveal v = 1 lifetimes of 3 ps for the asymmetric BH4(-) stretching mode ν3 and of 3.6 ps for the asymmetric bending mode ν4 in the solvent isopropylamine. We provide direct evidence for the BH4(-) stretching relaxation pathway via the asymmetric bending mode ν4 by probing the latter after femtosecond excitation of ν3. Pump-probe traces measured in the crystalline phase show signatures of radiative coupling between the densely packed BH4(-) oscillators, most clearly manifested in an accelerated subpicosecond depopulation of the v = 1 state of the ν4 mode. The radiative decay is followed by incoherent vibrational relaxation similar to the liquid phase. The excess energy released in the relaxation processes of the BH4(-) intramolecular modes is transferred into the environment with thermal pump-probe signals being much more pronounced in the dense solid than in the diluted solution.

Infrared spectroscopic study of Rb2M(XO4)2·6H2O (M = Mg, Co, Ni, Cu, Zn; X = S, Se) and of [formula omitted] guest ions included in rubidium Tutton selenates

The solubility in the three-component systems Rb2SeO4–MSeO4–H2O (M=Mg, Ni, Cu) is studied at 25°C by the method of isothermal decrease of supersaturation. It has been established that double compounds, Rb2M(SeO4)2·6H2O (M=Mg, Ni, Cu), crystallize from the ternary solutions within wide concentration ranges.Infrared spectra of rubidium Tutton compounds, Rb2M(XO4)2·6H2O (X=S, Se; M=Mg, Co, Ni, Cu, Zn) (in the region of 1300–400cm−1) as well as those of SO42- ions included in selenate matrices (up to 15mol%) in the region of the stretching modes ν3 and ν1 are presented and discussed. The matrix-isolated SO42- ions exhibit three bands for ν3 and one band for ν1 in good agreement with the low site symmetry C1 of the SeO42- host ions. The extent of energetic distortion of the isomorphously included ions as deduced from the values of Δν3 (site group splitting) and Δν3/νc (where νc is the centro-frequency value of the asymmetric stretches) is discussed. The comparison of the vibrational behavior of the matrix-isolated SO42- ions (about 2mol%) in different Tutton selenate matrices show that the distortions of the sulfate guest ions increase on going from potassium selenates to ammonium ones. The stronger distortion of the SO42- guest ions in ammonium compounds as compared to that of the same ions included in the potassium and rubidium selenates is due to the formation of hydrogen bonds between the guest ions and the NH4+ host cations additionally to those with water molecules of the host compound. The matrix-isolated sulfate guest ions are stronger distorted in the case of the Rb2Cu(SeO4)2·6H2O, (NH4)2Cu(SeO4)2·6H2O, (NH4)2Zn(SeO4)2·6H2O, and (NH4)2Ni(SeO4)2·6H2O as compared to those in the respective magnesium, cobalt and nickel selenate matrices is due probably to the formation of stronger hydrogen bonds in the former compounds (strong synergetic effect of the copper, zinc and nickel ions) as well as to the formation of hydrogen bonds between the guest ions and the ammonium host ions. The water librations are also briefly discussed.

Structure composition correlation in KNN–BT ceramics – An X-ray diffraction and Raman spectroscopic investigation

Lead free (1 − x)K0.5Na0.5NbO3–(x)BaTiO3 ceramics were synthesized by solid state reaction. The influence of the addition of BaTiO3 on the phase and crystalline symmetry of the KNN-based ceramics was investigated. X-ray analysis confirmed that the addition of BaTiO3 results in the change of structure from orthorhombic towards tetragonal at x = 0.04 and cubic phase above x = 0.1. The tetragonality ratio increased from 1.005 at x = 0.04 to 1.022 at x = 0.08 and then decreased. Raman spectra demonstrated a variety of changes with BT addition, mainly classified as lattice translations involving motions of the alkaline cations and internal modes of NbO6 octahedra. The symmetric stretching mode ν1 shifted to a higher wavenumber as the concentration of BT is increased, because the incorporation of BaTiO3 in the perovskite unit distorted the O–Nb–O bond angles. A linear relationship was observed in tetragonality ratio calculated by XRD and Raman shifts. This correlation between XRD and Raman spectroscopy results can be used to assess the crystalline symmetry in KNN-modified systems.

On the structure and the antisymmetric ν3 IR mode of covalent azide group

A new correlation ν3=1997+1.17×103 Δr between the stretching mode ν3 of the IR band frequency and the bond length asymmetry expressed as Δr≡r(Nα−Nβ)−r(Nβ−Nγ) is established in molecular azides RNαNβNγ with the correlation coefficient R=0.972. The database represents recent spectral and structural information for more than fifty organic molecules and inorganic metal complexes. Because the absolute term practically coincides with the ν3 frequency value for the free azide group, this correlation shows that the blue shift Δν3 (in cm−1) of the ν3 from the free azide value varies in direct proportion with the N3 group asymmetry Δr (in Å) (Δν3=1.17×103 Δr) at formation of different azide structures.

Crystal and molecular structure of ammonium beryllium sulfate dihydrate, (NH4)2Be(SO4)2·2H2O

In this paper we report the crystal and molecular structure of the title compound, (NH4)2Be(SO4)2·2H2O, as determined by single-crystal X-ray diffraction and vibrational spectroscopy data.(NH4)2Be(SO4)2·2H2O crystallizes in the monoclinic space group P21/c (a=11.448(2), b=11.876(2), c=7.439(1)Å, β=96.64(1)°, V=1004.6Å3, Z=4, R1=0.036 for 3753 Fo>4σ(Fo) and 185 variables), and is isotypic with the respective potassium and rubidium sulfates and the potassium selenate. The crystal structure is built from three-membered tetrahedral chain fragments, consisting of a central BeO2(H2O)2 group and two adjacent SO4 tetrahedra. These building blocks are linked by rather strong hydrogen bonds of the water molecules (O⋯O=2.66–2.77Å) and by moderate to weak hydrogen bonds of the NH4 groups (N⋯O≥2.78Å) to a three-dimensional framework structure.The infrared bands corresponding to the stretching modes ν3 and ν1 as well as the Raman band corresponding to ν1 of the SO42- ions are observed in the spectra as doublets, thus reflecting the existence of two crystallographically different sulfate ions. The spectroscopic experiments reveal that the sulfate tetrahedra exhibit a remarkably large extent of energetic distortion as deduced from the values of Δν3 (site group splitting) and Δνmax (the difference between the highest and the lowest wavenumbered component of the stretching modes) (111 and 183.5cm−1, respectively), which could not be predicted from the structural data. The comparison of the spectral region widths of the stretching and bending modes of the SO42- ions allows us to assume that these ions undergo a stronger energetic distortion with respect to the SO bond lengths than that with respect to the OSO bond angles. The water librations couple intensively with both the translatory modes of the Be2+ cations (BeO4 skeleton vibrations) and the normal modes of the sulfate ions, thus producing small isotopic shifts (for example, the ratio νr(H2O)/νr(D2O) has value of 1.12). The strength of the hydrogen bonds formed by the water molecules in the title compound is also commented in comparison with that of the hydrogen bonds in the respective isomorphous potassium and rubidium compounds.

Observation of the ν3 Raman band of S3− inserted into sodalite cages

AbstractThe S3− radical anion is observed in several systems: non‐aqueous polysulfides solutions, doped alkali halides, ultramarine pigments (UP) for which S3− is the blue chromophore and S2− is the yellow one and pigments of zeolite 4A structure. The S3− ion has C2V symmetry, and therefore its three vibrational modes should be observed in the Raman and in IR spectra. In resonance Raman spectroscopy, only the symmetric stretching mode ν1 and the bending mode ν2 have been observed, whereas the anti‐symmetric stretching mode ν3 has never been observed whatever the system. In this work, we confirm that ν3 is not observed in solutions with resonance Raman spectroscopy. However, our investigation of several blue UP, with various concentrations of S2−, shows that there is a superposition of two bands at ca 590 cm−1: the first is assigned to ν (S2−) and the second to ν3 (S3−). With the 457.9 nm excitation line, for which the resonance conditions are simultaneously fulfilled for S2− and S3−, the band at ca 590 cm−1 is the sum of the contributions of both ν (S2−) and ν3 (S3−) vibrations, while, with the 647.1 nm line, which only satisfies the resonance conditions of S3−, the band at ca 584 cm−1 must be assigned only to ν3 (S3−). Furthermore, ν3 (S3−) is observed in green UP and in pigments of zeolite structure. The ν3 vibration of S3−, which is observed neither in polysulfide solutions nor in doped alkali halides in resonance Raman conditions, can therefore be observed when this species is inserted into the β‐cages of the sodalite or of the zeolite 4A structures. So, the band at ca 590 cm−1 cannot always be assigned to S2− in these systems. This implies that the concentration of S2− in UP must be reconsidered. Copyright © 2007 John Wiley & Sons, Ltd.

The dependence of low-energy electron attachment to CF3Br on electron and vibrational energy

In a joint experimental and theoretical effort, we have studied dissociative electron attachment (DEA) to the CF3Br molecule at electron energies below 2 eV. Using two variants of the laser photoelectron attachment method with a thermal gas target (T(G) = 300 K), we measured the energy dependent yield for Br- formation over the range E = 3-1200 meV with resolutions of about 3 meV (E < 200 meV) and 35 meV. At the onsets for excitation of one and two quanta for the C-Br stretching mode nu3, downward cusps are detected. With reference to the recommended thermal (300 K) attachment rate coefficient k(A)(CF3Br) = 1.4 x 10(-8) cm3 s(-1), absolute cross sections have been determined for Br- formation. In addition, we studied Br- and (CF3Br)Br- formations with a seeded supersonic target beam (10% CF3Br in helium carrier gas, with a stagnation pressure of 1-4 bars and nozzle temperatures of 300 and 600 K) and found prominent structure in the anion yields due to cluster formation. Using the microwave pulse radiolysis swarm technique, allowing for controlled variation of the electron temperature by microwave heating, we studied the dependence of the absolute DEA rate coefficient on the mean electron energy E over the range of 0.04-2 eV at gas temperatures T(G) ranging from 173 to 600 K. For comparison with the experimental results, semiempirical resonance R-matrix calculations have been carried out. The input for the theory includes the known energetic and structural parameters of the neutral molecule and its anion; the parameters of the resonant anion curves are chosen with reference to the known thermal rate coefficient for the DEA process. For the gas temperature T(G) = 300 K, good overall agreement of the theoretical DEA cross section with the experimental results is observed; moreover, rate coefficients for Br- formation due to Rydberg electron transfer, calculated with both the experimental and the theoretical DEA cross sections, are found to agree with the previously reported absolute experimental values. At T(G) = 300 K, satisfactory agreement is also found between the calculated and experimental attachment rate coefficients for mean electron energies E = 0.04-2 eV. The strong increase of the measured rate coefficients with rising gas temperature, however, could be only partially recovered by the R-matrix results. The differences may result from the influence of thermal excitations of other vibrational modes not included in the theory.

High resolution low-energy electron attachment to CF3I

Using several variants of the laser photoelectron attachment method, we have measured the energy-dependent yield for I− formation resulting from dissociative electron attachment (DEA) to CF3I molecules over the energy range 0.5–500 meV. One approach involved a static target gas (TG = 300 K) and pulsed electron production/anion extraction. In another approach, a collimated target was provided by a differentially pumped, seeded supersonic beam (10% CF3I in helium carrier gas, stagnation pressure 1 bar, nozzle temperature 300 K and 600 K). At the onsets for excitation of one and two quanta for the C–I stretching mode ν3, clear downward cusps are detected. With reference to the recommended thermal DEA rate coefficient kA(Te = TG = 300 K) = 1.9 × 10−7 cm3 s−1, a new highly resolved absolute cross section for I− formation has been determined. Our experimental results are well reproduced by a cross section calculated in the framework of the resonance R-matrix theory. The input for the theory includes the known energetic and structural parameters of the neutral molecule and its anion and adopts a revised vertical attachment energy and a surface amplitude chosen to reproduce the thermal DEA rate coefficient. The theory is also applied to predict absolute cross sections for vibrational excitation of the C–I stretching mode ν3. Using our experimental and theoretical DEA cross sections we derive rate coefficients for Rydberg electron transfer (RET) and the dependence of the rate coefficients for free electron attachment of a Maxwellian electron ensemble on the mean electron energy from 0.002 to 2 eV at the constant gas temperature TG = 300 K; in both cases good agreement is observed with direct RET and swarm measurements.

Probing a strong hydrogen bond with infrared spectroscopy: Vibrational predissociation of BrHBr−⋅Ar

The gas phase vibrational spectroscopy of BrHBr−, a prototypical strongly hydrogen-bonded species, has been studied between 6 and 17 μm (590 and 1670 cm−1) by infrared vibrational predissociation of the BrHBr−⋅Ar ion. Infrared excitation was accomplished using the output of the free electron laser for infrared experiments (FELIX). Predissociation spectra were recorded by monitoring depletion of mass-selected BrHBr−⋅Ar ions as a function of excitation wavelength. Four prominent absorption bands are observed at 733, 890, 1048, and 1201 cm−1. They are assigned to the fundamental of the hydrogenic stretching mode ν3 and a sequence of ν3+nν1 combinations (n=1–3). Additional features to the blue of these bands spaced by ∼21 cm−1 are attributed to combination bands involving motion of the Ar messenger atom. Differences in the relative intensities of the ν3+nν1 combinations bands in comparison to previous matrix experiments are rationalized on the basis of the underlying dissociation dynamics.