High resolution microwave spectroscopy of the isomeric pair vinylcyanoacetylene and cyanovinylacetylene

The carbon chain molecules vinylcyanoacetylene and cyanovinylacetylene have been investigated between 8 and 41 GHz by Fourier transform microwave spectroscopy of a supersonic molecular beam. Owing to the high spectral resolution of the present technique, significantly more accurate rotational and centrifugal distortion constants have been derived for both molecules. In addition, the dipole moments have been calculated at the B3LYP/cc-pVTZ level of theory. Because these carbon chains are similar in structure and composition to known astronomical molecules and because of their high polarity, both species are good candidates for radioastronomical detection.     

Theoretical investigations of homo- and heteronuclear bridged fullerene oligomers

\chem{[C_{60}]_{\chemindex{n}}} -oligomers (, , and ) as well as dimers partially bridged by oxygen atoms or a group. The applicability of the scheme for finding the ground state of these systems was carefully checked against more sophisticated methods including an all-electron, self-consistent (SCF) scheme based on the local-density-approximation (LDA), and the recently developed generalized-gradient approximation (GGA). We present Raman intensities for the vibrations of the oligomers, obtained in the framework of the bond polarization model, and compare with recent experimental data. Received: 26 September 1996/Accepted: 16 December 1996     

Ag Raman modes of RBCO (R = Gd, Pr) by density functional theory approach

Ab initio total energy calculations have been performed for superconducting GdBa₂Cu₃O₇ and insulating PrBa₂Cu₃O₇ using the full-potential linear augmented plane-wave method in the local density approximation (LDA) and generalized gradient approximation (GGA). The comparison of the calculated unit cell volume and lattice parameters with the experimental data indicates the improvement of these parameters in the GGA relative to LDA. LDA and GGA give the equilibrium unit cell volume about 6% smaller and 1.25% larger than the experimental data, respectively for both systems. Thus frozen phonon calculations have been performed to determine the eigenvalues and eigenvectors of the k=0 A_g modes of the two systems in equilibrium structure have been obtained in GGA. The calculated frequencies in the GGA are in good agreement with the other LDA calculations for similar systems. Comparison of computational data with experimental data indicates that calculations determine the frequencies about ten percent below the experimental data. Even by improving LDA to GGA in these calculations, the calculated phonon frequencies have remained almost ten percent below the experimental data, even though the calculated unit cell volumes are nearly equal to the experimental data. So, applying GGA has not considerably decreased the difference between the computational and experimental data. The effect of Pr doping on the eigenvalues and eigenvectors have also been investigated.     

The conductance of SnO2 small nanowires: A study based on density functional and scattering theories

This study is motivated by the recent advances in the fabrication of oxide nanostructures and its purpose is the assessment of the relationship between their structural properties and the conductance. The structures considered are small SnO₂ nanowires whose size and shape reproduce on a smaller scale the structures produced by current technologies. Their electronic configuration and the conductance are evaluated using the density functional and scattering theories with a simplified modelling of the external leads. The study of the electronic configuration shows that the structure of the allowed energy levels and of the charges responds to the details of the nanowire structure and composition. These effects are important in the context of the conductance. In fact, deep resonances are produced by the alignment of the allowed energy levels in the nanowire with the ones in the external leads. For these conductive channels the relationship between the size and the conductance parallels the one between the size and the binding energy.     

Improved endohedral fullerenelike structures of silicon clusters Si31–Si39 by density functional calculations

We extensively search for the endohedral silicon-fullerene structures of Si₃₁–Si₃₉ using the combination of a tight-binding potential with the density functional theory. The resulting structures of our best candidates characterize more compact features comparing to previous isomers [J. Am. Chem. Soc. 126, 13845 (2004); J. Chem. Phys. 124, 164311 (2006)]. Most of our best candidates belong to new families featuring different core/cage combinations or different original carbon fullerene cages with respect to those of previous isomers. Energy calculations reveal that our best candidates are more stable than the previous best ones at the PW91 level, except for n = 34 and 38. The predicted relative stabilities of these isomers remain even at finite temperatures. In addition, the densities of dangling-bond atoms in the surfaces of our Si₃₃ and Si₃₉ isomers are significantly lower than the previous best candidates, as well as lower than those of their neighbors. This finding together with the densities of the active sites in the surfaces of the previous best candidates of Si₃₄ and Si₃₈ is roughly consistent with the observed relative reactivities of the silicon clusters in the size range of n = 31-39.     

Analysis of （1, 2） （1, 3） and （2, 3） Bands in the c^3Ⅱu- b^3Ⅱg System of P2

We investigate the high resolution absorption spectroscopy of P2 radical, generated in ac glow discharge of PC13 buffered with helium, using optical heterodyne magnetic rotation enhanced concentration modulation spectroscopy in the visible region. The （1, 2）, （1, 3） and （2, 3） bands of c^3Ⅱu- b^3Ⅱg in the range 16620-17860cm^-1 are observed and their 3II2 3II2 subbands are rotationally analysed. A set of effective molecular constants for the Ω= 2 component of the states involved are determined.     

Theoretical study of structural properties and dissociation pathways of FCN and ClCN

Geometrical parameters, harmonic frequencies and molecular properties of FCN, ClCN, their cations and the isomers of FCN and ClCN are studied in detail using ab initio MP2, CCSD and CCSD(T) methods. The dissociation energy of FCN and ClCN in various dissociation channels has been investigated. Both ground and metastable state of the fragmented atoms are considered in their dissociation pathways. The isomerization energy of FCN and ClCN and the NBO charges of FCN, ClCN, their cations and isomers are analyzed.     

The cleavage of the methane CH bond over PdO/H-BEA: A density functional theory study

Cluster models were used to represent the β-type cationic sites of the protonated beta zeolite (H-BEA) and the loading of PdO on these sites. The properties of these clusters and the cleavage of methane CH bond over these clusters were studied using density functional theory (DFT) method. The stability of H-BEA was enhanced due to the formation of hydrogen bonds. After PdO loading, the Pd atom bonds to four oxygen atoms among which three H-BEA framework oxygen atoms are included to form an approximate planar structure with Pd in the centre. This structure is very similar to that of bulk PdO. The acidic proton of H-BEA and the oxygen atom of PdO participate in the cleavage of methane CH bond, indicating that PdO is the active species for the activation of methane. Over the clusters constructed in the present work, the calculated energy barriers for the cleavage of methane CH bond are in the region between 17.54 and 21.02 kcal mol⁻¹.     

Density functional theory study of the electronic and field emission properties of nitrogen- and boron-doped carbon nanocones

Using first-principles density functional theory, we have investigated the electronic and field emission properties of carbon nanocones (CNCs) doped with N or B with 60° disclination. Our findings are that the emission properties for the doped CNCs depend on the doping species, position, and concentration. Compared to pristine CNC, N-doped CNCs exhibit better field emission properties, in which as the doping concentration increases from 1.25% to 2.5% the maximum emission current at applied electric field of 0.3 V/Å increases from 0.94 μA (one N atom is doped at the position adjacent to the pentagon) to 2.90 μA (two N atoms are doped at pentagon). As for pristine CNC the emission current is only 0.21 μA. However, B-doping has no significant influence on the emission properties of CNCs. Our findings suggest that N-doped CNCs can be used as a candidate for cold-emission electron sources.     

Systematic analysis of the Fourier transform spectrum of CH3OH between 400 and 950 cm

We have investigated a high-resolution Fourier transform (FT) absorption spectrum of the ¹³CH₃OH isotopomer of methanol from 400 to 950 cm⁻¹ with the “Ritz” program. We present the assignments of 7160 transitions, 3021 of which belong to A-symmetry, and 4139 to E-symmetry. These transitions occur between states labeled by K quantum numbers up to 14, and by torsional quantum numbers n up to 4. The “Ritz” program evaluated the energies of the 4684 involved levels with an accuracy of the order of 10⁻⁴ cm⁻¹. All of the assigned lines correspond to transitions involving torsionally excited levels within the ground small-amplitude vibrational state.     

Remote measurement of volcanic gases by Fourier transform infrared spectroscopy

Received: 25 March 1998     

Near-infrared cavity enhanced absorption spectroscopy of hot water and OH in an oven and in flames

A compact diode laser operating around 1.5 μm was used to measure cavity enhanced absorption spectra of hot water molecules and OH radicals in radiative environments under atmospheric conditions. Spectra of air were measured in an oven at temperatures ranging from 300 K to 1500 K. These spectra contained rovibrational lines from water and OH. The water spectra were compared to simulations from the HITRAN and HITEMP databases. Furthermore, spectra were recorded in the flame of a flat methane/air burner and in an oxyacetylene flame produced by a welding torch. The results show that cavity enhanced absorption spectroscopy provides a sensitive method for rapid monitoring of species in radiative environments. Received: 22 February 2001 / Revised version: 23 April 2001 / Published online: 7 June 2001     

Configurations, Electronic Structure and Magnetic Ordering of Small Manganese Clusters

We investigate the configurations, electronic structures, and magnetic ordering of MnN （N = 2-13） clusters based on all-electron density functional theory. The Jahn-Teller effect plays an important role in determining the ground state of certain geometries. The magnetic ordering of the MnN dusters transits from ferromagnetic ordering for the smallest （ N = 2, 3） dusters to a near degeneracy state including ferromagnetic and ferrimagnetic ordering in the vicinity of N = 4-6 and to a clear ferrimagnetic ordering at N = 7 or beyond. N = 6 and 10 are the magic numbers for neutrai MnN （N = 2-13） dusters.     

Catalyst poisoning in the conversion of CO and N 2O to CO 2 and N 2 on Pt 4 - in the gas phase

Pt₄ ^- catalyses the conversion of CO and N₂O to CO₂ and N₂ in the gas phase, as observed by Fourier transform ion cyclotron (FT-ICR) mass spectrometry. The partial pressures of CO and N₂O determine the extent of poisoning and the turnover numbers that can be achieved. The catalytic conversion terminates as soon as two CO are adsorbed on the cluster. With N₂O, the reactivity of Pt₄O₂ ^- and Pt₄O₃ ^- is reduced to 41% and 34% compared to Pt₄O^-, respectively, and with Pt₄O₄ ^- this value is reduced to 1%. In contrast, Pt₄ ⁺ shows no apparent catalytic activity. Density functional theory calculations of Pt₄ ^+/- with CO and N₂O adsorbates reveal significantly different stabilities of the reaction intermediates for the different charge states.     

Computer study of acetylene and ethane adsorption by disperse water medium

Adsorption of acetylene and ethane molecules by water clusters has been investigated by the molecular dynamics method at T=233 K. With the help of determination of statistical weights the cluster systems are created. In the frequency range of 0?ω?1000 cm⁻¹ the integral absorption coefficient of IR-radiation increases after the adsorption of acetylene or ethane molecules by the ultra disperse water system. The dissipation power of IR-radiation by cluster systems increases if C₂H₂ molecules are adsorbed, and it reduces in the case of C₂H₆ molecules' adsorption.     

Differential Helmholtz resonant photoacoustic cell for spectroscopy and gas analysis with room-temperature diode lasers

The results of theoretical and experimental studies and the design of a multi-purpose differential Helmholtz resonant photoacoustic detector (DHRD) and its applications to high-resolution spectroscopy of molecular gases and gas analysis with a room-temperature diode laser in the near-IR region are summarized. The series of experiments and numerical analysis of the DHRD sensitivity were performed for both types (single-pass and multi-pass) of DHRDs within a wide pressure range 0.1–101 kPa, including the regime of a gas flowing through a DHRD cell. The hardware and electronic arrangement of DHRDs for diode laser spectrometers and gas analyzers providing a limiting absorption sensitivity better than 10^-7 Wm^-1 are described. The results of measurements of spectral line parameters of H₂O near 800 and 1390 nm and CH₄ near 1650 nm (intensities, line broadening and shifting by atomic and molecular gases) are presented and discussed. The problems and the ways of perfection of the methodology and accuracy of DHRD techniques with tunable diode lasers of near-IR and visible spectral ranges are discussed. Received: 1 April 2002 / Revised version: 20 June 2002 / Published online: 21 August 2002 RID="*" ID="*"Corresponding author. Fax: +7/382-225-8026, E-mail: kvan@asd.iao.ru     

Rapidly swept, continuous-wave cavity ringdown spectroscopy with optical heterodyne detection: single- and multi-wavelength sensing of gases

Spectroscopic sensing of gases can be performed with high sensitivity and photometric precision by cavity ringdown (CRD) absorption spectroscopy. Our cavity ringdown spectrometer incorporates continuous-wave (cw) tunable diode lasers, fibre-optic coupling and standard photonics and optical telecommunications components. It comprises a rapidly swept optical cavity in a single-ended optical heterodyne transmitter–receiver configuration, enabling optical absorption of gases to be recorded either as single-frequency scanned spectra or as simultaneous, multi-wavelength tailored spectra. By measuring weak near-infrared rovibrational spectra of carbon dioxide gas (CO₂), with high resolution in the vicinity of 1.53 μm, we have realised a noise-limited absorption sensitivity of 2.5×10^-9 cm^-1 Hz^-1/2. Analytical sensitivity limits (both actual and projected) and prospective gas-diagnostic applications are discussed. Our approach to cw-CRD spectroscopy offers high performance in a relatively simple, low-cost, compact instrument that is amenable to chemical analysis of trace gases in medical, agricultural, industrial and environmental situations. Received: 16 May 2002 / Revised version: 3 June 2002 / Published online: 21 August 2002 RID="*" ID="*"Corresponding author. Fax: +61-2/9850-8313, E-mail: brian.orr@mq.edu.au     

Electronic states of neutral and ionized tetrahydrofuran studied by VUV spectroscopy and ab initio calculations

The electronic spectroscopy of isolated tetrahydrofuran (THF) in the gas phase has been investigated using high-resolution photoabsorption spectroscopy in the 5.8–10.6 eV with absolute cross-section measurements derived. In addition, an electron energy loss spectrum was recorded at 100 eV and 10° over the 5–11.4 eV range. The He(I) photoelectron spectrum was also collected to quantify ionisation energies in the 9–16.1 eV spectral region. These experiments are supported by the first high-level ab initio calculations performed on the excited states of the neutral molecule and on the ground state of the positive ion. The excellent agreement between the theoretical results and the measurements allows us to solve several discrepancies concerning the electronic state spectroscopy of THF. The present work reconsiders the question of the lowest energy conformers of the molecule and its population distribution at room temperature. Electronic supplementary material  Supplementary Online Material     

Hydrogen bonding in amylose/DMSO complexes studied by vibrational spectroscopy and density functional theory calculations

The intermolecular interactions in amylose/dimethyl sulfoxide (DMSO) complexes are discussed both experimentally and theoretically by means of Raman and infrared spectroscopies. The study is based on a preliminary analysis of well known systems such as pure liquid DMSO or DMSO in mixture with water: for such systems, an analysis of the CS stretching region is carried out both by means of Raman and infrared spectra. In particular, Raman spectra reveal a high sensitivity to the strength and to the type of interaction involving the DMSO molecules. These results, applied to the investigation of amylose‐DMSO complexes, show the presence of different hydrogen‐bonded complexes which coexist in this compound. In particular, DMSO molecules are identified both on the external surface of the V‐amylose helix, where they can interact via one hydrogen bond and in the inner channel of the helix where they can interact via two hydrogen bonds. The present findings open the possibility of applying vibrational spectroscopy to the characterization of inclusion compounds of amylose which are currently being involved in many fields of nanosciences. Copyright © 2009 John Wiley & Sons, Ltd.