Vibrational Dipole Research Articles

Theoretical study on the structures, isomerization and stability of SiC3H isomers

The calculations of the geometry optimizations, energies, dipole moments, vibrational spectra, rotational constants, and isomerization of doublet SiC3H species were performed using density functional theory and ab initio methods. Four types of isomers, a total of 18 minima, connected by 16 interconversion transition states, were located on the potential energy surface (PES) at the B3LYP/6-311G (d, p) level. More accurate energies were obtained at the CCSD(T)/6-311G(2df, 2p), and G3(MP2) levels. With the highest isomerization barrier, the lowest lying structure, linear A1 possesses the largest kinetic stability. Besides, the isomerization barriers of A2, A4, C2, F1, F4 and F5 are over 10 kcal/mol, and these isomers are also considered to be higher kinetically stable. Other isomers cannot be kinetically stabilized with considerably low isomerization barriers. Investigation on the bonding properties and the computations of vibrational spectra, dipole moments, and rotational constants for SiC3H isomers are helpful for understanding their structures and also valuable for their detections in the interstellar space and laboratory.

Internal Vibrations of Edge Dislocation Dipoles

The resonance frequency of vibrations of dislocation dipoles in fatigued f.c.c. metals is found rather high, in the range of 100 GHz. Because of high attenuation of ultrasound in the GHz range, the contributions of these self-vibrations to degradation of the dipole structures could be expected only in thin layers.

Pressure broadening and shifting parameters for the spectral lines in the fundamental vibration–rotation bands of HBr and HI in mixtures with rare gases

We report measurements of the line broadening and shifting coefficients in the (1 ← 0) fundamental absorption bands of the HBr and HI molecules in mixtures with rare gases He, Ne, Ar, Kr, and Xe. Comparison is given with the published data on other HHal–Rg systems. The measured line shifts are separated into terms symmetric and asymmetric in the line number m. The magnitudes of the symmetric shifts change in a regular manner in the series of rare gases and reach perturber-specific asymptotic values at higher ∣ m∣. It is found that the asymptotic values of the symmetric line shifts linearly correlate with the respective C 6 potential energy constants and that the slopes of these correlations are proportional to the vibrational ground state dipole moments squared of the hydrogen halide molecules.

Structural and electronic changes of cytosine upon addition of atomic sulfur

When sulfur becomes a contaminant it may affect important biophysical and biochemical processes. In this work, we investigate the interaction of cytosine with atomic sulfur. We find two equally probable places where sulfur may link cytosine. The changes in energetics and variations in the vibrational spectra, dipole moment, charge populations and electron density with respect to isolated cytosine are quantified. The computations are performed according to the Kohn–Sham version of density functional theory. We conclude on the possibility that sulfur may locally interfere in the formation of the Watson–Crick pairs and in the stacking of contiguous nucleic acid bases of the DNA/ RNA helix.

Multisensor Processing Algorithms for Underwater Dipole Localization and Tracking Using MEMS Artificial Lateral-Line Sensors

An engineered artificial lateral-line system has been recently developed, consisting of a 16-element array of finely spaced MEMS hot-wire flow sensors. This represents a new class of underwater flow sensing instruments and necessitates the development of rapid, efficient, and robust signal processing algorithms. In this paper, we report on the development and implementation of a set of algorithms that assist in the localization and tracking of vibrational dipole sources underwater. Using these algorithms, accurate tracking of the trajectory of a moving dipole source has been demonstrated successfully.

Theoretical Investigation of the (Hyper)polarizabilities of Pyrrole Homologues C4H4XH (X = N, P, As, Sb, Bi). A Coupled-Cluster and Density Functional Theory Study

Geometries, inversion barriers, static and dynamic electronic and vibrational dipole polarizability (alpha), and first (beta) and second (gamma) hyperpolarizability of the pyrrole homologues C(4)H(4)XH (X = N, P, As, Sb, Bi) have been calculated by Hartree-Fock, Møller-Plesset second-order perturbation theory, coupled-cluster theory accounting for singles, doubles, and noniterative triple excitations methods, as well as density functional theory using B3LYP and PBE1PBE functionals and Sadlej's Pol and 6-311G basis sets. Relativistic effects on the heavier homologues stibole and bismole have been taken into account within effective core potential approximation. The results show that the electronic (hyper)polarizabilities monotonically increase with the atomic number of the heteroatom, consistent with the decrease in the molecular hardness. Ring planarization reduces the carbon-carbon bond length alternation of the cis-butadienic unit, enhancing the electronic polarizability values (alpha(e)) by 4-12% and the (hyper)polarizability values (and gamma(e)) by 30-90%. Pure vibrational and zero-point vibrational average contributions to the (hyper)polarizabilities have been determined within the clamped nucleus approach. In the static limit, the pure vibrational hyperpolarizabilities have a major contribution. Anharmonic corrections dominate the pure vibrational hyperpolarizabilities of pyrrole, while they are less important for the heavier homologues. Static and dynamic electronic response properties of the pyrrole homologues are comparable to or larger than the corresponding properties of the furan and cyclopentadiene homologue series.

Infrared absorption enhancement of fluorinated poly‐acrylate thin films on Co‐alloy substrate

AbstractFluorinated poly‐acrylate films coated on continuous Co‐based metal substrate show significant IR absorption enhancement. The degree of enhancement depends greatly on the type of chemical bonds in the polymer molecules and the corresponding vibrations of chemical dipoles. Strong polar groups like CO, CF and CO show the strongest absorption enhancement that also coincides with significant blueshift of the corresponding IR bands. In this paper, the possible mechanism for IR absorption enhancement and band shift are discussed on the basis of the electric field intensification on metal surface, charge transfer and dipole reorientation of the polymer molecules adsorbed on the metal surface. Chemisorption of the polymer molecules on Co‐alloy is established through the interaction between the oxygen atoms in carboxylic group and the substrate cobalt atoms reacting through electron overlap and spin‐coupling of oxygen π‐orbital and cobalt d‐orbital. Copyright © 2006 John Wiley & Sons, Ltd.

Structure and Stability of Isomers of the Promising Interstellar Molecule PC3O

DFT/B3LYP/6-311G(d) and CCSD(T)/6-311G(2d) single-point calculations are carried out for exploring the doublet potential energy surface (PES) of PC3O, a molecule of potential interest in interstellar chemistry. A total of 29 minima connected by 65 interconversion transition states are located. The structures of the most relevant isomers and transition states are further optimized at the QCISD level followed by CCSD(T) single-point energy calculations. At the CCSD(T)/6-311G(2df)//QCISD/6-311G(d)+ZPVE level, the global minimum is the quasi-linear structure PCCCO 1 (0.0 kcal/mol) with a great kinetic stability of 47.9 kcal/mol, and the cumulenic form $${\mathop P\limits_ - ^ \bullet}=C=C=C={\mathop O\limits_ - ^ -}$$ features largely in its resonance structures. Moreover, the chainlike isomer OPCCC 3 (64.5) and five-membered-ring species cPCCCO 19 (77.8) possess considerable kinetic stability of about 18.0 kcal/mol. All these three isomers are very promising candidates for future experimental and astrophysical detection. Additionally, a three-membered-ring isomer CC-cCOP 10 (69.6) has slightly lower kinetic stability of around 15 kcal/mol and may also be experimentally observable. Possible formation mechanisms of the four stable isomers in interstellar space are discussed. The present research is the first attempt to study the isomerization and dissociation mechanisms of PC n O series. The predicted spectroscopic properties, including harmonic vibrational frequencies, dipole moments and rotational constants for the relevant isomers, are expected to be informative for the identification of PC3O in laboratory and interstellar medium.

Vibrational assignment and dipole moment derivatives of hexafluorobenzene between 4000 and 250 cm −1

The liquid phase vibrational assignment and dipole moment derivatives of hexafluorobenzene are reported. These are obtained by fitting the imaginary molar polarizability spectrum of hexafluorobenzene to classical damped harmonic oscillator bands. Most of the observed transitions were assigned to infrared active fundamentals or binary combinations. From the active combination transitions, the wavenumbers of the inactive fundamentals were obtained. In addition, ab initio calculations at the CCD/cc-pVDZ level of theory were used to determine the harmonic force field and dipole moment derivatives of gaseous hexafluorobenzene. It was determined that in the gas phase ∂μ y / ∂s 1=−5.53 Debye Å −1, ∂μ x / ∂t 2=1.03, ∂μ x /∂β 1=0.78, and ∂μ z /∂γ 1=0.57 Debye Å −1 while in the liquid ∂μ y / ∂s 1=−4.00 Debye Å −1, ∂μ x / ∂t 2=1.27, and ∂μ x /∂b 1=0.50 Debye Å −1. ∂μ z /∂γ 1 could not be determined for the liquid phase because the fundamental is below the limits of the current measurements. The differences between the liquid and gas phase dipole moment derivatives of hexafluorobenzene were found to be consistent with the differences previously reported for benzene.

Rotary motor powered by stochastic uncorrelated dipoles

It is demonstrated that the stochastic back-and-forth vibrations of uncorrelated dipoles may lead to rotation of their ambient dipoles. This peculiar phenomenon is clarified by considering spatial and temporal symmetry breakings. The former asymmetry is the result of the multiple biased Hamiltonian vector fields, which is a ratchet effect, and the latter, of the time sequence specified by a metastable state. Since this driving mechanism is simpler than that of F0F1ATPase, it could benefit the design of nanometer scale rotary devices.

Polarized Microwave Radiation from Dust

Observations of cosmic microwave background in the range 10-90 GHz have revealed an anomalous foreground component well correlated with 12 μm, 60 μm and 100 μm emission from interstellar dust. As the recent cross-correlation analysis of WHAM Hα maps with the Tenerife 10 and 15 GHz maps supports an earlier conclusion that the emission does not arise from free-free radiation, the interstellar dust origin of it is left as the only suspect. Two competing models of this emission exist. The more favored at the moment is the spinning dust model, the other is the model that uses grains with strong magnetic response. In the spinning dust model the emission arises from rapid rotation of ultrasmall grains that have dipole moments, while in the other model magnetic grains emit due to thermal vibrations of magnetic dipoles. Both models predict the emission to be partially polarized and this emission can seriously interfere with the CMB polarization measurements. We discuss observational signatures that can be used to distinguish and eventually filter out the polarized component of the microwave dust radiation.

Comparison of the cis-bending and C–H stretching vibration on the reaction of C2H2+with H2using laser induced reactions

Laser induced reaction (LIR) of C2H2(+) + H2 in a 22-pole ion trap at 90 K has been employed to detect the v3 C-H stretching vibration and the v5 cis bending vibration of the acetylene parent ion using the wide tunability of the free electron laser FELIX. The vibrational frequency of the bending vibration, omega5, and the corresponding Renner-Teller parameter, epsilon5, are determined to be 710 cm(-1) and 0.03, respectively. These results differ quite substantially from previous experimental work but are in line with the most recent and advanced theoretical work. The dependence of the LIR-signal of the two vibrational modes is studied systematically with respect to the laser power, storage time, and number density of the hydrogen collision partner. A reaction scheme describing all steps involved in the LIR process is set up. The corresponding rate equation system is solved numerically. From this solution the lifetimes for the vibrational excited states, tau3 = (3 +/- 1) ms and t5 = (200 +/- 50) ms and the vibrational dipole moments micro3 = 0.19(2) D and micro2 = 0.21(2) D are determined under the assumption that the excited parent ion relaxes or reacts with a net rate coefficient equal to the Langevin limit. The lifetime for the C-H stretching vibration is in agreement with a previous LIR experiment and with ab initio calculations. C-H stretching turns out to be about an order of magnitude more efficient than bending in promoting hydrogen abstraction. This strong mode dependence is discussed on the basis of the energetics for hydrogen abstraction and a possible inhibition of complex formation in the entrance channel of the C2H2+..H2 collision system.

Study of hydrogen bond polarized IR spectra of cinnamic acid crystals

This paper presents the results of investigation of the polarized IR spectra of cinnamic acid and of its deuterium derivative crystals. The spectra were measured by a transmission method, using polarized light, at the room temperature and at 77 K, for two different crystalline faces. Theoretical analysis of the results concerned linear dichroic effects, H/D isotopic and temperature effects, observed in the spectra of the hydrogen and of the deuterium bonds in cinnamic acid crystals, at the frequency ranges of the ν O–H and the ν O–D bands. The basic crystal spectral properties could be satisfactorily interpreted in a quantitative way for a centrosymmetric cyclic hydrogen bond dimer model. Such a model explains not only a two-branch structure of the ν O–H and ν O–D bands in crystalline spectra, but also some essential linear dichroic effects in the band frequency ranges, measured for isotopically diluted crystals. Model calculations, performed within the limits of the ‘strong-coupling’ model, allowed for quantitative interpretation and for understanding of the basic properties of the hydrogen bond IR spectra of cinnamic acid crystals, H/D isotopic, temperature and dichroic effects included. In the scope of our studies the mechanism of H/D isotopic ‘self-organization’ processes, taking place in the crystal hydrogen bond lattices, was also recognized. It was proved that for isotopically diluted crystalline samples of cinnamic acid, a non-random distribution of protons and deuterons occurs exclusively in the hydrogen bond dimers. Nevertheless, these co-operative interactions between the hydrogen bonds do not involve the adjacent hydrogen bond dimers in each unit cell. The two-branch fine structure pattern of the ν O–H and ν O–D bands was ascribed to the vibronic mechanism of vibrational dipole selection rule breaking in centrosymmetric hydrogen bond dimers. The observed in the spectra very high intensity of the forbidden transition sub-band in the analyzed ν O–H and ν O–D bands is a manifestation of an extremely effective symmetry rule breaking mechanism. It correlates with a relatively large excess electron charge on the cinnamic aid dimer carboxyl groups. This effect is a result of a partial withdrawal of the electron charge, from the conjugated π-bond systems of the styryl substituents, by the carboxyl groups. This statement has been supported by ab initio calculations.

Polarization of phosphorescence transitions and probabilities of intramolecular nonradiative deactivation of the lowest triplet state of aromatic molecules

This study continues the experimental testing of the validity of the inductive resonance theory of dipole-dipole energy transfer from the T 1→S 0 transition dipole to stretching vibrations of intramolecular CH bonds of naphthalene and its hydroxy derivatives. To this end, in the series of compounds under study, the range of variation of the geometrical parameter [Φ(CH)]2 of the Forster theory, which accounts for the mutual orientation of the energy donor and acceptor, is estimated. Preliminarily, the angles between the transition dipole moments of the radiative and absorptive electronic transitions (T 1→S 0 and S 0→S 1; T 1→S 0 and S 0→S 2; S 1→S 0 and S 0 →S 1; and S 1→S 0 and S 0→S 2) are measured at 77 K by the method of polarization photoselection. From the polarization measurements, the angles between the phosphorescence transition dipole moment and the plane of a molecule are determined. It was found that, upon passage from naphthalene to its β derivatives, the orientation of the dipole moment of the radiative T 1→S 0 transition relative to the plane of a molecule markedly changes, with the in-plane component of the dipole moment being increased by an order of magnitude. The experimentally determined rate constants of nonradiative deactivation of the T 1 state averaged over the CH groups of the naphthalene ring system, k nr(CH), are compared with the rate constants [Φ(CH)]2 of the inductive resonance energy transfer from the dipole of the T 1→S 0 transition to the dipole of the CH vibrations polarized in the plane of a molecule, calculated with regard to the orientational factor [Φ(CH)]2. This comparison showed that, in the series of compounds under study, a change in the orientation of the dipole moment of the radiative T 1→S 0 transition relative to the plane of a molecule does not affect the rate of the nonradiative T 1⇝S 0 transition. This inference is confirmed by the absence of a correlation between the rate constants k dd(CH) calculated by us (with regard to [Φ(CH)]2) and the well-known rate constants k nr(CH) of individual sublevels of the T 1 state measured at T≤1.35 K for a number of organic molecules. The possible sources of discrepancy between the experimental data that k nr(CH) is independent of [Φ(CH)]2 and the predictions of the theory are considered. A conclusion is made that the electronic-vibrational energy transfer between electric dipoles is the most probable mechanism of the T 1⇝S 0 transitions, but the rate constant of the dipole-dipole energy transfer upon interaction of the electronic and vibrational dipoles in a molecule does not depend on their orientations.

Structures of HCN-Mgn (n=2-6) complexes from rotationally resolved vibrational spectroscopy and ab initio theory.

High-resolution infrared laser spectroscopy has been used to determine the structures of HCN-Mgn complexes formed in helium nanodroplets. The magnesium atoms are first added to the droplets to ensure that the magnesium complexes are preformed before the HCN molecule is added. The vibrational frequencies, structures, and dipole moments of these complexes are found to vary dramatically with cluster size, illustrating the nonadditive nature of the HCN-magnesium interactions. All of the complexes discussed here have the nitrogen end of the HCN pointing towards the magnesium clusters. For Mg3, the HCN binds to the "threefold" site, yielding a symmetric top spectrum. Although the HCN-Mg4 complex also has C3v symmetry, the HCN sits "on-top" of a single magnesium atom. These structures are confirmed by both ab initio calculations and measurements of the dipole moments. Significant charge transfer is observed in the case of HCN-Mg4, indicative of charge donation from the lone pair on the nitrogen of HCN into the lowest unoccupied molecular orbital of the Mg4.

Structure and Properties of the Open-Chain Calcium-Doped Carbon Clusters CaCn, CaCn+, and CaCn- (n = 1−8)

A DFT theoretical study of the CaC n , CaC n +, CaC n - (n = 1-8) open-chain clusters has been carried out using the B3LYP method with both 6-311G(d) and 6-311+G(d) basis sets. For each species several molecular properties such as vibrational frequencies, dipole moments, and rotational constants are reported. For the CaC n open-chain clusters the lowest-lying states correspond to triplet states for n-odd members, whereas in the n-even species the ground states were found to be singlets. Cationic clusters have doublet ground states with the exception of the smallest one, CaC + . In CaC n - clusters, except for CaC 3 -, the ground state is alternate between quartets (for n-odd members) and doublets (for n-even members). The incremental binding energy diagrams show a clear odd-even alternation in the cluster stability in both neutral and anionic clusters with their n-even members being more stable than the corresponding n-odd ones, while the parity effects is less pronounced for the cationic clusters. This odd-even alternation was also found for the electron affinities, whereas there is not a clear alternation in the ionization potentials.

Molecular isomerization induced by ultrashort infrared pulses. I. Few-cycle to sub-one-cycle Gaussian pulses and the role of the carrier-envelope phase.

Using 550 previously calculated vibrational energy levels and dipole moments we performed simulations of the HCN-->HNC isomerization dynamics induced by sub-one-cycle and few-cycle IR pulses, which we represent as Gaussian pulses with 0.25-2 optical cycles in the pulse width. Starting from vibrationally pre-excited states, isomerization probabilities of up to 50% are obtained for optimized pulses. With decreasing number of optical cycles a strong dependence on the carrier-envelope phase (CEP) emerges. Although the optimized pulse parameters change significantly with the number of optical cycles, the distortion by the Gaussian envelope produces nearly equal fields, with a positive lobe followed by a negative one. The positions and areas of the lobes are also almost unchanged, irrespective of the number of cycles in the half-width. Isomerization proceeds via a pump-dumplike mechanism induced by the sequential lobes. The first lobe prepares a wave packet incorporating many delocalized states above the barrier. It is the motion of this wave packet across the barrier, which determines the timing of the pump and dump lobes. The role of the pulse parameters, and in particular of the CEP, is to produce the correct lobe sequence, size and timing within a continuous pulse.

Structure and vibrations of the CF3NO molecule in the ground and lowest excited electronic states: A test of ab initio methods

AbstractEquilibrium geometries, harmonic vibrational frequencies, and barriers to internal rotation of the CF3NO molecule in the ground singlet (S0) and lowest excited triplet (T1) and singlet (S1) electronic states are calculated using various ab initio techniques and compared with the experimental data. The sensitivity of the results to the choice of atomic orbital basis set, in particular, to the presence of f‐symmetry functions, and to the dynamical correlation treatment is analyzed. Anharmonic vibrational frequencies and dipole moment of the CF3NO molecule in the ground state are computed. The results of all approaches employed are in good agreement with each other and with available experimental data. Conclusions concerning the accuracy of different methods are drawn. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004

Structures and stability of isomers of [Si, N, N, P] system

Some stationary points on the potential energy surface of [Si, N, N, P] system were located at the B3LYP/6-311G(d) and QCISD(t)/6-311+G(2df)(single-point) levels of theory, while the isomerization, structures, and stability of these obtained isomers were suggested. The computed results indicate that only four-membered ring isomer SiNPN(E1, 2 A″), which possesses butterfly-like structure and Si-P cross bonding, is kinetically stable in all optimized isomers. Other isomers may be considered as kinetically unstable towards isomerization or dissociation because of the corresponding smaller reaction barriers. Furthermore, the present paper also proposes electronic and geometric structures, vibrational frequencies and the corresponding vibrational modes, dipole moments, and rotational constants of isomer E1 . To make use of the computed results, we can clearly know that the reaction pathway via an intermediate E3 (SiNPN) is the most favorable channel producing isomer E1 from fragments SiN ( 2 Π) and PN ( 1 Σ), which have been well characterized in space, and thus, isomer E1 can be considered as a candidate for interstellar observation. The reaction enthalpy of SiN ( 2 Π) + PN( 1 Σ)→ E1 and the standard enthalpy of formation of isomer E1 are 215.25 and 457.99 kJ/mol, respectively, at 298.15 K.

Structure and stability of BC 2P isomers: a theoretical study

A theoretical study of the different BC 2P isomers has been carried out on both singlet and triplet surfaces. A linear isomer, corresponding to the PBCC connectivity and to a 3Σ electronic state, is predicted to be the global minimum. In addition we have found five other structures lying quite close in energy, less than 10 kcal/mol. In particular a rhombic isomer, formed through the interaction of a phosphorus atom with a BC 2 cyclic unit through a B–C side, is shown to lie just about 2 kcal/mol higher in energy than the linear isomer. Predictions for the vibrational frequencies, rotational constants, dipole moments, and dissociation energies for the linear and rhombic isomers have been made. In both cases a relatively high value of more than 80 kcal/mol is obtained for their fragmentation into P+BC 2, showing that these species are relatively stable and consequently of potential experimental interest.