Vibrational Dipole Research Articles

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.

Line intensities of the: ν3, 4 ν2, ν1+ ν3, 3 ν1 and 2 ν1+2 ν2 bands of 16O 12C 32S molecule

The line intensities of the ν 3 band of OCS used for atmospheric retrievals, has been measured. The spectra have been recorded with the Reims Fourier transform spectrometer. Other bands of OCS 4ν 2, ν 1+ν 3, 3ν 1 and 2 ν 1+2 ν 2 were recorded to obtain the line intensities. The results are compared to usual databanks (HITRAN or GEISA). From the measured line intensities, it has been possible to estimate the square of the vibrational dipole moment matrix element ( in debye 2) , equal to 0.1313 1, 7.840 9×10 −4, 1.158 1×10 −3, 1.218 3×10 −5, 1.192 3×10 −5 , respectively, for ν 3, 4ν 2, ν 1+ν 3, 3ν 1 and 2 ν 1+2 ν 2.

ATOMICCLUSTERS AS ABRANCHOFNUCLEARPHYSICS

▪ Abstract The conduction electrons in clusters of simple metal atoms are approximatively independent and free. Nucleons in nuclei also behave as delocalized and independent fermions. This generic behavior generates analogies between metal clusters and nuclei, such as the shell structure, the shapes, and the dipole vibration mode. However, there are also major differences that arise from the presence of ions in metal clusters. Fission of nuclei and clusters, and particle emission from them, reveal these differences.

Infrared spectroscopic study of molecular hydrogen bonding in chiral smetic liquid crystals

We utilize Fourier transform infrared (IR) spectroscopy to probe intramolecular hydrogen bonding in smectic‐C* liquid crystal phases. Infrared spectra of aligned smectic liquid crystal materials vs. temperature and of isotropic liquid crystal mixtures vs. concentration were measured in homologs, both with and without hydrogen bonding. Hydrogen bonding significantly changes the direction and magnitude of the vibrational dipole transition moments, causing marked changes in the IR dichroic absorbance profiles of hydrogen bonded molecular subfragments. A GAUSSIAN94 computation of the directions, magnitudes, and frequencies of the vibrational dipole moments of molecular subfragments shows good agreement with the experimental data. The results show that IR dichroism can be an effective probe of hydrogen bonding in liquid crystal phases.

Dipole moments of highly vibrationally excited HCN: Theoretical prediction of an experimental diagnostic for delocalized states

Vibrational state specific dipole moments are diagnostic of the degree of localization of vibrational states in highly vibrationally excited HCN. Using a newly calculated global ab initio dipole moment function and previously calculated highly accurate vibrational wave functions, we show that delocalized (i.e., isomerizing) vibrational states of HCN possess markedly lower dipole moments than localized HCN or HNC states. We also show that the vibrational quantum number dependence of the dipole moment can be used to distinguish delocalized states from localized Franck–Condon-dark states that are made observable by perturbations with localized Franck–Condon-bright states. Furthermore, using classical trajectory analysis we introduce and describe a new experimental approach to obtain these data, which relies on combining optical pumping and state specific molecular transport with hexapoles. With this method it is possible to determine state specific dipole moments with high accuracy and precision.

Quantum calculation of the dipole excitation in fusion reactions.

The excitation of the giant dipole resonance induced by fusion reaction is studied with N/Z asymmetry in the entrance channel. The time dependent Hartree-Fock solution exhibits a strong dipole vibration which can be associated with a giant vibration along the main axis of the deformed compound nucleus. This dipole motion appears to be nonlinearly coupled to the shape oscillation, leading to a strong modulation of its frequency. These phenomena can be detected in the gamma-ray emission from hot compound nuclei.

A variety of properties of the [formula omitted] excited state of PF computed by configuration interaction calculations

Extended basis set configuration interaction calculations on the first known excited state (a 1Δ) of PF have been performed and are presented for the first time. A variety of properties are reported including: (i) spectroscopic constants; (ii) vibrational energies and anharmonicity parameters ( ΔG v+1/2 ); (iii) rotational excitations; (iv) selected one-electron properties such as the electric multipole moments, the 17F electric nuclear quadrupole coupling, the second moments of the charge distribution, etc.; (v) vibrational electric dipole moments; (vi) cascade vibrational lifetimes. Good agreement is obtained with the restricted number of experimental data available. The accuracy of the present results is discussed and compared with that obtained for the X 3Σ − ground state and related homologous diatomics.

Is HCCP linear, bent or cyclic? Structures and energies of its low-lying states

Ab initio and density functional theory (DFT) calculations have been carried out to predict the structures and to estimate the energies of the low-lying states of HCCP. The geometrical parameters, harmonic vibrational frequencies, IR intensities, dipole moments and rotational constants of the energetically favorable isomers have been estimated with the (U)HF, (U)MP2, ROHF, CAS(2,2) and DFT methods using the 6-31G ∗ [(U)HF, ROHF and CAS(2,2)], 6-31G(2df,p) (UHF), cc-pVDZ [(U)MP2] and cc-pVTZ[(U)MP2 and DFT] basis sets. At the B3LYP/cc-pVTZ geometries, single point energy calculations were performed in the same basis set at the CISD (single and double excitation configuration interaction) and the CCSD(T) (coupled-cluster with all single and double substitutions, and a quasi-perturbative estimate for the effect of connected triple excitations) higher levels of theory. Linear HCCP ( 3Σ −) is found to be the global minimum at all the theoretical levels used. The second most stable isomer with a 1A′ electronic state is predicted to have a cyclic CCP structure in which the hydrogen atom is attached to the carbon atom. This state lies 18 and 14 kcal/mol above the triplet linear HCCP at the CISD and CCSD(T) levels, respectively. However, the other isomer of which hydrogen atom is attached to the phosphorous atom (CCPH, 1A′) is found to be much higher in energy than the ground state by 45 and 39 kcal/mol, respectively.

Configuration interaction calculations of miscellaneous properties of the [formula omitted] excited state and related [formula omitted] transition bands of phosphorus monoxide

Extended basis set configuration interaction calculations on the excited state ( C ′ 2Δ ) and several C ′ 2Δ– X 2Π r transition bands of phosphorus monoxide have been performed. A variety of molecular properties are reported including: (i) spectroscopic constants; (ii) vibrational energies of the C ′ 2Δ -state, transition band energies of several C ′ 2Δ– X 2Π r bands and related Franck–Condon parameters; (iii) selected one-electron properties such as the electric multipole moments, 17 O nuclear quadrupole coupling, anisotropic hyperfine parameters, etc; (iv) vibrational electric dipole moments; (v) C ′ 2Δ vibrational lifetimes through cascade and via electric dipolar decays C ′ 2Δ→ X 2Π r . Good agreement is obtained with the available limited amount of experimental data. The accuracy of the present results is discussed and compared to that obtained for the X 2Π r -state and for excited states of homologous diatomics.

Miscellaneous property computations on the [formula omitted]-state of phosphorus monofluoride by configuration interaction calculations

Extended basis set configuration interaction calculations on the ground state of phosphorus monofluoride PF( X 3Σ − ) have been achieved. Several properties are reported, classified as follows: (i) spectroscopic constants; (ii) vibrational energies and related anharmonicity parameters; (iii) pure rotational excitations; (iv) selected one-electron properties such as electric multipole moments, anisotropic hyperfine parameters, 17F nuclear quadrupole coupling and others; (v) vibrational dipole moments; (vi) cascade vibrational lifetimes. Good agreement is obtained with the restricted number of experimental data available. A comparison is made between the accuracy of the present results and that of analogous diatomics for which supplementary experimental data have been reported.

Infrared spectroscopic study of molecular hydrogen bonding in chiral smectic liquid crystals

We report the use of Fourier-transform infrared (IR) spectroscopy to probe intermolecular and intramolecular hydrogen bonding in thermotropic liquid-crystal phases. Infrared spectra of aligned smectic liquid crystal materials vs temperature, and of isotropic liquid-crystal mixtures vs concentration were measured in homologs both with and without hydrogen bonding. Hydrogen bonding significantly changes the direction and magnitude of the vibrational dipole transition moments, causing marked changes in the IR dichroic absorbance profiles of hydrogen-bonded molecular subfragments. A GAUSSIAN94 computation of the directions, magnitudes, and frequencies of the vibrational dipole moments of molecular subfragments shows good agreement with the experimental data. The results show that IR dichroism can be an effective probe of hydrogen bonding in liquid-crystal phases.

Compact hydrogenated amorphous germanium films by ion-beam sputtering deposition

We explore reactive ion-beam sputtering deposition (IBSD) for the growth of a-Ge:H films. It is shown that compact a-Ge:H films can be obtained by IBSD at substrate temperatures between 180°C and 220°C by minimizing the ion bombardment of the growth surface. The infrared (IR) spectra of the best materials, as far as device applications are concerned, so-far obtained show no poly-hydride nor surface-like contributions to the Ge–H dipole vibration bands. Positron annihilation (PA) spectroscopy studies of these samples reveal smaller valence ( S) parameters and larger core ( W) parameters as compared with the films grown under less-favorable conditions, which indicate a relatively smaller concentration of the largest voids, the annihilation process being controlled mainly by trapping at small vacancy clusters or monovacancies. Similar IR and PA measurements on in situ ion-bombarded IBSD and RF-sputtered samples indicate that ion irradiation is a main factor in large void formation.

Periodic trends in the diatomic monoxides and monosulfides of the 3d transition metals

Non-local, density functional calculations have been performed on the ground and low-lying excited states of the 3d transition metal monoxide and monosulfide molecules. Periodic trends in properties such as bond lengths, bond energies, vibrational force constants and dipole moments are examined. The variations in the bond lengths and energies are compared to those in the monoxide and monosulfide solids. Analysis of the electronic structures of the molecules reveals the d-orbital splitting to be dπ > dσ ≥ dδ and shows the non-bonding role of the dσ and dδ functions. This sequence mirrors that in the electronically related dichloride molecules and leads to similarities in the periodic trends with those in the solids. Systematic errors in the calculated bond energies and vibrational frequencies are identified. The successful use of a correctly parameterized ligand-field model is reported allowing quantitative reproduction of the ‘d–d’ spectra of the monoxide molecules and the prediction of band positions of unassigned transitions.

The High-Resolution FTIR Spectrum of the ν1 Band of DOBr

Fourier transform infrared spectra of the ν1 bands of DO79Br and DO81Br have been recorded with a resolution of 0.0055 cm−1 in the frequency range of 2510–2800 cm−1. A total of 1901 lines of the A/B hybrid-type bands of both isotopic species have been assigned and fitted to upper state rovibrational constants employing a Watson's S-reduced Hamiltonian up to sextic terms. The Ka ≥ 4 subband transitions were found to be perturbed and were not included in the fit. The unperturbed band centers for ν1 of DO79Br and DO81Br are 2668.79211 ± 0.00006 and 2668.78842 ± 0.00005 cm−1, respectively. The ratio of the vibrational dipole transition moments (μa:μb) was found to be 1.30 ± 0.04 for the band.

Vibrational Stark Spectroscopy 3. Accurate Benchmark ab Initio and Density Functional Calculations for CO and CN-

A new Stark-type experimental technique known as electroabsorption spectroscopy has been developed in S. G. Boxer's laboratories which offers the ability to measure the responses of isotropic solvated molecules to an applied electric field. It is applicable to a wide range of molecules and environments. We present benchmark ab initio and density-functional calculations employing 14 methods and double-ζ to penta-ζ augmented basis sets for the vibrational frequencies, dipole moment, polarizability, hyperpolarizability profiles, Stark shift, and other electroabsorption properties of two important (gas-phase) molecules, CO and CN-, for which a range of high-precision experimental data is available. The results show excellent agreement with these data, verify the earlier conclusion that the transition-moment polarizability rather than the polarizability change dominates the first-derivative response in the electroabsorption spectroscopy of these systems, and convergence with respect to the treatment of electro...

Configuration interaction calculations of miscellaneous properties of the X 2r ground state, the C´ 2 excited state and related C´ 2-X 2r transition bands of PO: I. X 2r ground state

Extended basis set configuration interaction calculations on the ground state (X 2r) of PO have been performed. A wide variety of molecular properties are reported, including: (i) spectroscopic constants; (ii) vibrational energies and anharmonicity effects; (iii) pure rotational transitions for several (J´,J´´) sets and the first 11 vibrational quantum numbers; (iv) one-electron properties such as the electric dipole/quadrupole moments, nuclear quadrupole (17O) coupling, anisotropic hyperfine parameters, etc; (v) vibrational electric dipole moments µv; (vi) cascade 2r vibrational and rovibrational lifetimes. Good agreement is obtained with the available limited amount of experimental data. Finally, the accuracy of the present results is discussed and compared to that obtained for the CP(X 2+) state.

Structures and Stabilities for Halides and Oxides of Transactinide Elements Rf, Db, and Sg Calculated by Relativistic Effective Core Potential Methods

The ground states of the halides and oxides containing transactinide elements Rf (element 104), Db (element 105), and Sg (element 106) were calculated at the HF, MP2, QCISD, CCSD, and CCSD(T) levels of theory using one- and two-component relativistic effective core potentials. Spin−orbit effects are rather small for geometries, harmonic vibrational frequencies, charge distributions, overlap populations, and dipole moments, but considerable for atomization energies. Electron correlations are necessary for any accurate determination of the molecular properties, in particular for the evaluation of atomization energies. The bond lengths of Sg compounds are consistently longer than those of the corresponding W compounds by 0.04−0.06 Å. The atomization energies for Sg compounds are slightly smaller than those for the corresponding W compounds due to spin−orbit and correlation effects. The differences tend to increase with the number of oxygen atoms in the compounds. Metal charges and dipole moments are larger for the Sg compounds than for the W compounds, implying that Sg is more ionic than W. The D3h structures are calculated to be more stable by about 2 kcal/mol than the C4v ones for TaCl5, TaBr5, DbCl5, and DbBr5.

Vibrational Assignment and Dipole Moment Derivatives of Liquid Bromobenzene at 25 °C

The previously published optical constants of bromobenzene were used to calculate the imaginary molar polarizability spectrum. The imaginary molar polarizability spectrum was fit to 163 classical damped harmonic oscillator bands between 3240 and 140 cm-1, the vast majority of which were obvious in the experimental spectrum. With the aid of the previous fundamental assignments in the literature and the force field for liquid benzene, the first thorough assignment of liquid bromobenzene is presented. The integrated intensities, transition moments, and dipole moment derivatives with respect to normal coordinates of the fundamentals were calculated from the fitted bands. These transition moments and dipole moment derivatives are compared with those in the literature for benzene-d. The transition moments and dipole moment derivatives are significantly different in these substituted benzenes, indicating that either the eigenvectors for the vibrations are different in the two molecules or that dipole moment derivatives with respect to internal coordinates are different in the two molecules. This will be analyzed further in a future paper.

Ultrafast Structural Response of Hydrogen Bonded Complexes to Electronic Excitation in the Liquid Phase

The response of hydrogen bonded complexes to electronic excitation is studied by site-specific vibrational spectroscopy in the femtosecond domain, providing insight into local changes of hydrogen bonding geometries. For the prototypical organic complex coumarin 102−(phenol)1,2 in solution, electronic excitation of the coumarin chromophore initiates a response of intermolecular hydrogen bonds on two distinct time scales: the hydrogen donor (phenol)1,2 is released from the acceptor coumarin within 200 fs, followed by a reorganization of the (phenol)2 moiety with an 800 fs time constant. This structural response results in strong changes of vibrational dipole moments which are monitored for the first time.

Structures, Vibrational Frequencies and Polarizabilities of Diazaborinines, Triazadiborinines, Azaboroles, and Oxazaboroles

Ab initio, second-order, Møller−Plesset perturbation theory calculations of the equilibrium geometries, harmonic vibrational frequencies, relative stabilities, dipole moments, and static dipole polarizabilities are reported for 70 different 6π-electron monocycles containing boron and nitrogen. These include 26 azaborinines isosteric to pyridine, 16 azaboroles, and 28 oxazaboroles. The most stable isomers have the substructure XBHNH, where X = N, NH, or O is the base-ring heteroatom. Planar conformations are stable minima for all but 15 five-membered rings. Lower level calculations are unreliable in predicting which molecules are planar. Good agreement is found with the available electron diffraction and X-ray structures of substituted rings. Additive atom and bond polarizability models which are accurate to within a few percent are constructed for a larger set of 104 planar molecules, including azines, azoles, oxazoles, and azaborinines isosteric to benzene. The presence of boron causes scatter of the polarizabilities of isomers; hence the additive models of polarizability are less accurate than if only heterocycles containing C, N, and O are included.