Vibrational Splittings Research Articles

Fine vibrational structure in core-to-bound spectra of polyatomic molecules

Near-edge x-ray-absorption fine-structure (NEXAFS) spectra of 1-butene (C4H8), acrylonitrile (C2H3CN) and 1,3-butadiene (C4H6) multilayers were recorded with high resolution (better than 100 meV at the carbon edge) and a theoretical method to interpret the vibrational structure of the observed C1s→π* bands is presented. The method is based on local (quadratic) approximations for the potential energy surfaces of both ground and excited electronic states, with input data obtained by ab initio calculations of normal modes for the ground state and energy gradients for the excited state within the framework of the equivalent core model. The method proved to be useful in qualitative terms, providing information on the nature of the excited modes and on the geometrical changes following the electronic excitation. We have also calculated the C1s→π* spectrum of ethylene (C2H4) and compared it to those obtained for C4H8, C2H3CN, and C4H6. Since the latter can be considered as substituted ethylenes, the validity of the building-block scheme for the vibrational splittings in inner-shell absorption spectra could be assessed by this comparison.

Detection of the syn conformer of allyl alcohol by free jet microwave spectroscopy

The rotational spectrum of allyl alcohol has been investigated with a free jet millimeter wave spectrometer in the frequency range 60–78 GHz. The spectra of the normal and OD monodeuterated species of the syn conformer have been assigned. They are characterized by the tunneling splittings due to the hydroxyl group internal rotation. These vibrational splittings amount to 14168.15 and 937.66 MHz for the normal and deuterated species, respectively.

Vibrational and ligand-field effects in the high resolution core-level spectroscopy of molecules

High resolution Si2p and Br3d core-level spectra of small molecules (photoabsorption, photoelectron and Auger) all show fine structure due to vibrational or ligand field splitting. The Si2p photoelectron and photoabsorption spectra of SiH 4, SiD 4 and Si 2H 6 show rich vibrational structure from both the symmetric and the asymmetric SiH(D) vibrational modes. The symmetric ν 1 vibrational mode dominates the photoelectron spectra of SiH 4 ( ν 1 = 2379 cm −1) and SiD 4 ( ν 1 = 1710 cm −1). In contrast, the asymmetric bending mode is more dominant in the photoabsorption spectra of the early Rydberg levels of SiH 4 and SiD 4 and completely dominant in both the photoelectron and photoabsorption spectra of Si 2H 6. In contrast, the core-level spectra of heavy elements such as Br and I are dominated by ligand field splitting. The high resolution Br 3d photoelectron spectrum of HBr shows the 3 d 3 2 doublet and 3 d 5 2 triplet characteristic of ligand field splitting. This same splitting is shown to dominate the previously recorded MVV Auger spectrum and the pre-edge Br 3d photoabsorption spectrum.

The inversion barrier in NF+⋅3

Ab initio molecular orbital theory has been used to investigate the barrier to inversion in NF+̇3. Complete geometry optimizations have been carried out with a variety of basis sets and electron correlation methods. It is shown that for this problem the use of single-point energy calculations needs to be treated with caution. Discrepancies amongst previous theoretical values are shown to be due to the use of inappropriate geometries and inadequate inclusion of electron correlation. With a variety of quantum chemical methods, the barrier to inversion is predicted to be in the range 11.3–13.3 kcal/mol. We have also predicted the vibrational splittings for the NF+̇3 potential energy surface and attempted to reconcile the differences with experiment.

Study of the boron-oxygen units in crystalline and molten barium metaborate by high temperature Raman spectroscopy

The vibrational spectra of the boron-oxygen structural elements in single crystal β-BaB 2O 4 and BaB 2O 4 melts were studied by high temperature Raman spectral analysis. The experimental Raman peaks were assigned to the calculated normal vibrational modes of the free [B 3O 6] molecular unit. The observed vibrational mode splittings were found to be consistent with C 6 3 v symmetry for β-BaB 2O 4. Experimental vibrational spectra were compared with those of LiBO 2 and CsBO 2 in order to determine the temperature-dependent populations of chain, ring, and tetrahedral structural elements in the respective melts, and these in turn were shown to correlate with the degree of melt supercooling required for spontaneous crystallization to occur.

Coherent Raman observations of factor group splittings and lattice vibrations in nanocrystals formed in supersonic expansions

Coherent anti-Stokes Raman spectra are reported for solid, nanometer-sized C2H2 and CO2 aggregates formed in free jet expansions. From comparisons with spectra of equilibrium samples, the clusters are seen to be face centered cubic with a crystalline character indicated by the appearance of vibrational factor group splittings and, for CO2, by the observation of two external lattice librations.

ClF2: Structure and infrared spectra of a weakly bound triatomic molecule

Using sophisticated ab initio methods, the equilibrium structure of the ClF2 radical has been predicted to be bent, confirming previous experimental and theoretical work. The single, double and perturbative triple excitation coupled cluster level of theory along with a triple-ζ plus double polarization basis set gives the geometrical parameters re=1.756 Å and θe=151.8°. At the same level of theory, harmonic vibrational frequencies were predicted to be 536, 243, and 568 cm−1 for the symmetric stretch, bend and asymmetric stretch, respectively. In addition to this high level study of the harmonic vibrational frequencies, theoretical analyses of anharmonic terms have been included in order to help settle the controversy surrounding experimental assignments of the fundamental vibrational frequencies. This research supports Mamantov’s experimental assignment of the bending and symmetric stretching fundamental, over the experimental objections of Prochaska. The vibrational frequency splitting due to 37ClF2 was also studied indicating that only the splitting of the bending and asymmetric stretching modes should be readily observable experimentally. Dipole moments and infrared (IR) intensities were also predicted.

Angular dependence of loss intensities in inelastic electron scattering for physisorbed CO on Ag(110)

The a 3Π and A 1Π excitations of a physisorbed disordered bilayer of CO on Ag(110) have been investigated by means of electron energy loss spectroscopy (EELS) as a function of electron incidence angle and scattering angle and primary electron energy. Whereas in the (sub)monolayer regime these electronic excitations are quenched because of adsorbate-substrate interactions, strong losses with a clearly resolved vibrational splitting are observed at coverages above a monolayer. The intensities of these excitations behave differently as a function of the experimental geometry, which can be explained by the different characters of the excitations, i.e. one is optically allowed whereas the other is optically forbidden. The role the electron trajectories play for the ratio of the cross-sections of these two excitations is discussed, including electron-image charge interaction and diffraction effects.

Ligand-field splittings and core-level linewidths in I 4d photoelectron spectra of iodine molecules

High-resolution I 4d photoelectron spectra (total instrumental resolution ∼0.06 eV) of seven simple iodine molecules, ICl, IBr, I2, HI, CH3I, CH2I2, and CF3I, have been recorded. Ligand-field splitting (as measured by the asymmetric C20 crystal-field term) splits the 4d3/2 and 4d5/2 lines into a doublet and triplet, respectively. In contrast to Si 2p spectra, the I 4d spectra generally show little evidence for vibrational splitting or broadening. The C20 values, like the binding energies E4d, generally increase as the ligand electronegativity increases. C20 also correlates well with the nuclear field gradient, eqn, as measured by Mössbauer spectroscopy or nuclear quadrupole resonance. For the first time we have been able to study the chemical dependence of the inherent lifetime width of a core hole. We show that the I 4d linewidths generally decrease as the electronegativity of the ligand increases, and as the valence I 5p electron density decreases. We also show that there are large relaxation effects on E4d, C20 and especially the linewidth.

The relative importance of vibrational and ligand field splittings on core d-level photoelectron and NVV Auger spectra: high resolution core level photoelectron spectrum of the I 4d level of HI

A high resolution I 4d photoelectron spectrum (total instrumental resolution (60 meV) of HI is reported. The resolved splitting of the 4d9 final state is shown to be due to ligand field and not vibrational splitting. Previously reported I 4d photoelectron and NVV Auger spectra of HI (Karlsson et al) are reinterpreted based on the ligand field splitting of the I 4d core level. The presence of valence electron relaxation in hydrogen halides is shown to be an important influence on the magnitude of core level ligand field splitting and inherent linewidth.

Vibrational mode-specific tunneling splittings in the A states of deuterated tropolones

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTVibrational mode-specific tunneling splittings in the A states of deuterated tropolonesHiroshi Sekiya, Yusuke Nagashima, Takeshi Tsuji, Yukio Nishimura, Akira Mori, and Hitoshi TakeshitaCite this: J. Phys. Chem. 1991, 95, 25, 10311–10317Publication Date (Print):December 1, 1991Publication History Published online1 May 2002Published inissue 1 December 1991https://doi.org/10.1021/j100178a015RIGHTS & PERMISSIONSArticle Views127Altmetric-Citations74LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (774 KB) Get e-Alerts

The interaction of rotation and local mode tunneling in the overtone spectra of symmetrical hydrides

In the ‘‘local mode limit’’ where the tunneling time for vibrational energy exchange is long compared to the classical rotational period, one expects that the effective rotational Hamiltonian will reflect the reduced symmetry of the local mode state. Hamiltonians in the local mode basis are given for interaction of rotation and local mode tunneling for molecules of the XH2, XH3, and XH4 type. Transformation of these Hamiltonians to a symmetrized basis (which diagonalizes the vibrational problem), produces rotational couplings between the vibrational states. Relations between the spectroscopic constants are derived that are less restrictive than those given earlier by Halonen and Robiette, but reduce to them when the assumptions of their model are met. The present algebraic procedure can be easily extended to include higher order terms. The effect of these couplings is to reduce the size of the pure vibrational splittings. This is due to the fact that in the rovibrational problem, in general, one must reorient the angular momentum vector in the body frame as well as transfer the vibrational action between bonds. This increases the length of the tunneling path and thus decreases the rate of vibrational energy transfer. Model calculations show that a simple semiclassical picture can rationalize the observed trends.

Anomalous hydrogen dynamics in rare earth metals

Neutron scattering studies of the dynamics of the hydrogen isotopes in h.c.p. rare earth metals have demonstrated a rich variety of phenomena of basic importance to the understanding of hydrogen in metals. In this paper we review our recent measurements of hydrogen vibrations in yttrium using inelastic neutron scattering and our very recent investigations of hydrogen local hopping in scandium and yttrium using quasielastic neutron scattering. Using simple models we attempt to provide a straightforward but fairly comprehensive picture of the way extended hydrogen short range order, observed directly in diffuse neutron scattering experiments, influences these measurements. We show, for example, how the vibrational peak splitting measured in α-YHx can be interpreted in terms of temperature- and concentration-dependent effects of the chain-like pairing order. We also describe in detail our recent demonstration of very fast local T-T hopping in α-ScHx and in α-YHx and relate the observations to the identification of thermodynamically distinct labile (uninvolved in extended order) and non-labile (involved in extended order) hydrogens. In particular, we measure a pronounced T-T hopping rate minimum at 100 K, which we ascribe to the labile protons and show how the low temperature hopping rate is described by the Kondo model of quantum hopping due to the non-adiabatic effects of weak interaction between the protons and the conduction electrons of the host metal.

Vibrational splittings for hydrogen atom exchange in hydroperoxo radical: the effect of oxygen-oxygen displacement and vibration

The hydroperoxyl radical, HO{sub 2}, has been the subject of numerous experimental and theoretical studies. The interest in HO{sub 2} arises primarily from its importance in combustion reactions; it is the intermediate in the reaction H+O{sub 2} {yields} O+OH, which initiates chain-branching ignition phenomena in the oxidation of H{sub 2} and most hydrocarbon fuels. Using a global potential energy surface for HO{sub 2}, the authors calculate vibrational levels up to and slightly above the energy corresponding to the potential barrier for hydrogen atom exchange for both the two-mode (excluding the O-O vibration) and three-mode (including all three vibrations) cases. They examine the vibrational splittings for hydrogen atom exchange as a function of the energy; for the two-mode calculations they consider the effect on these splittings of O-O displacement while for the three-mode calculations the effect of O-O vibration is considered.

Anomalous hydrogen dynamics in rare earth metals

Neutron scattering studies of the dynamics of the hydrogen isotopes in h.c.p. rare earth metals have demonstrated a rich variety of phenomena of basic importance to the understanding of hydrogen in metals. In this paper we review our recent measurements of hydrogen vibrations in yttrium using inelastic neutron scattering and our very recent investigations of hydrogen local hopping in scandium and yttrium using quasielastic neutron scattering. Using simple models we attempt to provide a straightforward but fairly comprehensive picture of the way extended hydrogen short range order, observed directly in diffuse neutron scattering experiments, influences these measurements. We show, for example, how the vibrational peak splitting measured in α-YH x can be interpreted in terms of temperature- and concentration-dependent effects of the chain-like pairing order. We also describe in detail our recent demonstration of very fast local T-T hopping in α-ScH x and in α-YH x and relate the observations to the identification of thermodynamically distinct labile (uninvolved in extended order) and non-labile (involved in extended order) hydrogens. In particular, we measure a pronounced T-T hopping rate minimum at 100 K, which we ascribe to the labile protons and show how the low temperature hopping rate is described by the Kondo model of quantum hopping due to the non-adiabatic effects of weak interaction between the protons and the conduction electrons of the host metal.

Infrared optical properties of (TMTSF)2ReO4 and (TMTSF)2BF4 (where TMTSF is tetramethyltetraselenafulvalene) compared with several model calculations.

We report high-resolution reflectivity measurements of the protonated and deuterated forms of (TMTSF${)}_{2}$${\mathrm{ReO}}_{4}$ and (TMTSF${)}_{2}$${\mathrm{BF}}_{4}$, where TMTSF is tetramethyltetraselenafulvalene, at 300 and 25 K, and for polarizations E\ensuremath{\parallel}a and E\ensuremath{\parallel}b', from 30 to 8000 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$. Comparison of the spectra allowed assignments to be made for the many detailed vibrational features in the 25-K E\ensuremath{\parallel}a spectra, which are dominated by the electron-coupled totally symmetric (${\mathit{a}}_{\mathit{g}}$) modes. The data were fitted to several model calculations, including the ``dimer'' model, the ``tetramer'' model, the ``phase-phonon'' model, and a ``twofold-commensurate charge-density-wave'' model. The latter gave excellent agreement for the unsplit vibrations in both compounds, with the only variable being the semiconducting energy gaps of 1120 and 1700 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ for the ${\mathrm{BF}}_{4}$ and ${\mathrm{ReO}}_{4}$ compounds, respectively. The one-dimensional density of states clearly favors the energy-band description over the isolated charge-transfer mechanism. The nature of the vibrational splittings due to the anion ordering is discussed.

Vibrational spacings for HO2 and vibrational splittings for hydrogen atom exchange

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Conformation and ring inversion in γ-butyrolacetone. Part 2.—Ab initio and flexible model computations

The conformation and ring inversion of γ-butyrolactone have been studied using ab initio and flexible model computations. The potential energy surface has been computed using STO-3-21G orbitals and complete geometry optimization as a function of the ring puckering coordinates. The computed equilibrium geometry has a ring in which all of the atoms with the exception of the β carbon are nearly coplanar. The computed inversion barrier is 6.1 kJ mol–1. Analytical expressions, as functions of the correct symmetry of the ring puckering coordinates, have been obtained for the potential energy surface and internal coordinates by least-squares fits to the computed molecular energies and geometries. These data have been used as the input for flexible model computations of the vibrational frequencies, inversion splittings and rotational constants. By using a simple uniform scaling of the potential energy surface good agreement with the observed vibrational frequencies and inversion splittings is obtained for a barrier to ring inversion of 7.9 kJ mol–1. The changes in the rotational constants are reasonably well reproduced for excitation of the vibration which is associated with a double minimum potential and less successfully for the other ring puckering vibration.

High resolution molecular gas phase photoelectron spectra of core levels using synchrotron radiation - vibrational and ligand field splittings

A new high resolution photoelectron spectrometer designed for core level photoelectron studies of gas phase volatile and involatile compounds using synchrotron radiation is briefly described. Xenon NOO Auger spectral linewidths of 0.13 eV indicate that the electron resolution is < 0.05 eV. The Xe 4d photoelectron linewidth of ≈0.20 eV, for an inherent linewidth of ⩾ 0.13 eV, shows that the photon width is close to the theoretical 0.12 Å (0.09 eV at 94 eV). This resolution is sufficient to observe, for the first time, vibrational splitting of the Si 2p core level of SiH 4 and ligand field splitting of the Xe 4d core level of XeF 2.

Conformation and ring inversion in γ-butyrolactone. Part 1.—Microwave spectrum

The microwave spectrum of γ-butyrolactone has been reinvestigated in order to determine small vibrational splittings associated with the ring inversion. For the ground vibrational state the inversion splitting has been measured directly as 30.3 MHz by the observation of the µc rotation–inversion transitions. The inversion splitting in the first excited state of the two ring puckering vibrations has been determined through analysis of a type Coriolis interactions. In the first excited state of the 148 cm–1 vibration the inversion splitting is 609 MHz while for the 225 cm–1 it is 2930 MHz. These inversion splittings indicate that the 148 cm–1 vibration is associated with a single minimum potential function and the 225 cm–1 vibration with a double minimum potential function but that there is some interaction between the two vibrations. A one-dimensional reduced potential function has been derived for the 225 cm–1 vibration and gives a barrier to ring inversion of 8.0 kJ mol–1(670 cm–1).