bluuebunny/crossref_metadata_2025 huggingface dataset:
Collisions and reactions of ultracold molecules
Authors: Stwalley William C
Published: October 2004

It is argued that collision dynamics of atoms and molecules at ultracold temperatures (below 1 mK) are not readily predictable from knowledge of collision dynamics above 100 K. In the case of elastic collisions, it is well known that the collision cross section is constant as T → 0 K but mass and symmetry effects are dramatic. The cases of inelastic and reactive collisions are less studied, but a T1/2 dependence of the cross section as T → 0 K is expected. It seems that extrapolations of high-temperature inelastic and reactive behavior normally greatly underestimate ultracold-temperature rates. The prospects for experimental observation of ultracold collision dynamics are rapidly improving.Key words: ultracold molecules, collisions, reactions, hydrogen, scattering length.
New applications of the genetic algorithm for the interpretation of high-resolution spectra
Authors: Meerts W Leo , Schmitt Michael , Groenenboom Gerrit C
Published: October 2004

Rotationally resolved electronic spectroscopy yields a wealth of information on molecular structures in different electronic states. Unfortunately, for large molecules the spectra get rapidly very congested owing to close-lying vibronic bands, other isotopomers with similar zero-point energy shifts, or large-amplitude internal motions. A straightforward assignment of single rovibronic lines and, therefore, line position assigned fits are impossible. An alternative approach is unassigned fits of the spectra using genetic algorithms (GAs) with special cost functions for evaluation of the quality of the fit. This paper decribes the improvements we established on the GA method discussed before (J.A. Hageman, R. Wehrens, R. de Gelder, W.L. Meerts, and L.M.C. Buydens. J. Chem. Phys. 113, 7955 (2000)). In particular, we succeeded in obtaining a dramatic reduction in computing time that made it possible to apply the GA process in a large number of cases. A completely automated fit of a rotationally resolved laser-induced fluorescence spectrum without any prior knowledge of the molecular parameters can now be performed in less than 1 h. We demonstrate the power of the method on a number of typical examples such as very dense rovibronic spectra of van der Waals clusters and overlapping spectra due to different isotopomers. The discussed results demonstrate the extreme power of the GA in automated fitting and assigning of complex spectra. It opens the road to the analysis of complex spectra of biomolecules and their building blocks. Key words: high-resolution spectroscopy, genetic algorithm, biomolecules, structure, van der Waals clusters.
Configuration of ring-down spectrometers for maximum sensitivity
Authors: Jakubinek Michael , Tong Zhaoguo , Manzhos Sergei , Loock Hans-Peter
Published: October 2004

Cavity ring-down (CRD) spectrometers used for analytical applications frequently have design requirements different from spectrometers used for gas-phase spectroscopic applications. A formalism that allows for maximization of the relative sensitivity by adapting the cavity length and absorption path through the sample is presented. These experimental configurations may not reduce the detection limit but do allow for a high sensitivity of the ring-down time measurement in the concentration range of interest. The formalism is applied to two common CRDS experimental configurations and to a fiber-loop ring-down experiment.Key words: cavity ring-down (CRD), absorption, detector, fiber-loop, sensitivity, detection limit.
Measurement of the autoionization lifetime of the superexcited atomic sulfur S(3s23p3(2Do)4d) state using tunable vacuum ultraviolet (VUV) radiation
Authors: Huang Jianhua , Xu Dadong , Stuchebrukhov Alexei , Jackson William M
Published: October 2004

A new method is described that combines a tunable coherent vacuum ultraviolet (VUV) radiation source and an ion velocity imaging apparatus to study the autoionization of superexcited sulfur atoms. The photolysis of CS2 at 193 nm is used to produce metastable sulfur atoms in the 1D2 state. The S(1D2) atom is then directly excited to the neutral superexcited state 3s23p3(2Do)4d (1Do2) at 11.317 eV with a tunable VUV photon at ~121.896 nm. This excited state then undergoes autoionization into the first ionization continuum state of S+(4So3/2) + e, which is not directly accessible from the S(1D2) state through optical transition. By monitoring the S+ signal in the time-of-flight mass spectrometer while scanning the excitation wavelength, the line profile of the 3s23p34d 1Do2 ← 3s23p4 1D2 transition is recorded and found to have a full width at half maximum (FWHM) of 0.9 cm1. This has been used to determine an autoionization lifetime of the neutral superexcited 3s23p34d 1Do2 state of 5.9 ps. The accurate measurement of the autoionization lifetime provides a benchmark for testing fundamental theoretical models of processes occurring in excited states of atoms. Key words: autoionization, atomic sulfur, vacuum ultraviolet (VUV), full width at half maximum (FWHM).
The ν1 and ν2 vibrational bands of the OCCN radical detected through time-resolved Fourier transform IR emission spectroscopy
Authors: McNavage William , Dailey William , Dai Hai-Lung
Published: October 2004

Through monitoring the IR emission from vibrationally excited radicals generated by exothermic photolysis reactions, the CN stretch (ν1) and the CO stretch (ν2) vibrational bands of the cyanooxomethyl radical (OCCN) have been observed for the first time at 2093 cm1 and 1774 cm1, respectively. The OCCN radical was produced through 193 nm photolysis of methyl cyanoformate (NCC(O)OCH3), carbonyl cyanide (NCC(O)CN), and pivaloyl cyanide (NCC(O)C(CH3)3). The IR emission spectra were recorded by using nanosecond time-resolved Fourier transform IR emission spectroscopy. Assignments of the spectral peaks were made based on observed time and pressure dependences of IR emission intensities, ab initio calculations, and two-dimensional cross-spectra correlation analysis. Key words: radical, cyanooxomethyl, OCCN, time-resolved vibrational spectroscopy, FTIR, substituted carbonyl dissociation reactions, two-dimensional cross-spectra correlation analysis
Highly accurate transition frequencies in the H2 Lyman and Werner absorption bands
Authors: Philip J , Sprengers J P , Pielage Th. , de Lange C A , Ubachs W , Reinhold E
Published: October 2004

The transition frequencies of low-J excitation lines in the B1Σu+ X1Σg+,(ν′,0) Lyman bands have been measured for ν′ = 218 and in the C1ΠuX1Σg+,(ν′,0) Werner bands for ν′ = 04, using a narrow-band tunable extreme UV laser source at wavelengths λ = 92105 nm in conjunction with the technique of 1 +  1′ two-photon ionization. The measurements can be divided into three categories for which varying absolute accuracies were obtained. Special focus was on the B, ν′ = 25 bands, where an accuracy of 0.004 cm1 or δv/v = 4 x 108 is achieved. For transitions to B, ν′ ≤ 13 and C, ν′ ≤ 3 states the accuracy is 0.005 cm1 or δv/v = 5 x 108. Due to a different frequency mixing scheme uncertainties for B, ν′ ≥ 13 and C, ν′ = 4 are at the level of 0.011 cm1 or δv/v = 1.1 x 107. Inspection of combination differences between R(J) and P(J + 2) lines shows that the accuracies are even better than estimated in the error budget. Based on the measurements of 138 spectral lines and the known combination differences, transition frequencies of 60 P-lines could be calculated as well, so that a data base of 198 accurately calibrated lines results for the Lyman and Werner bands of H2. Key words: vacuum UV, molecular spectroscopy, hydrogen, precision metrology.
The antisymmetric stretching fundamental band of free MgD2
Authors: Shayesteh Alireza , Appadoo Dominique RT , Gordon Iouli , Bernath Peter F
Published: October 2004

The gaseous MgD2 molecule has been synthesized for the first time in an electrical discharge inside a high-temperature furnace. The high-resolution infrared emission spectrum of MgD2 was recorded with a Fourier transform spectrometer, and the antisymmetric stretching mode (v3) was detected near 1176.5 cm1. The v3 band was rotationally analyzed, and the r0 MgD bond distance was determined to be 1.700 874(8) Å.Key words: gaseous MgD2, vibration-rotation emission spectrum, Mg-D bond distance.
Infrared photodissociation spectroscopy of Si+(CO2)n and Si+(CO2)nAr complexes  Evidence for unanticipated intracluster reactions
Authors: Jaeger J B , Jaeger T D , Brinkmann N R , Schaefer H F , Duncan M A
Published: October 2004

Si+(CO2)n and Si+(CO2)nAr ionmolecule complexes were produced by laser vaporization in a pulsed supersonic expansion. The ions were mass-selected in a reflectron time-of-flight spectrometer and studied with infrared photodissociation spectroscopy near the asymmetric stretch vibration of CO2. Si+(CO2)n clusters fragment by the loss of CO2 whereas Si+(CO2)nAr complexes fragment by the loss of argon. All clusters have resonances near the CO2 asymmetric stretch, but with shifts in frequency that are size dependent. The patterns seen in the small clusters are consistent with electrostatic bonding, while the larger systems provide evidence for an intracluster reaction forming oxide-carbonyl species. Density functional theory was employed to examine the structures of these clusters, and their calculated vibrational frequencies were compared to the measured values. Ligand assembly in Si+(CO2)n complexes is dominated by the presence of the occupied 3p valence orbital of the silicon cation. Key words: ionmolecule complexes, infrared spectroscopy, photodissociation, density functional theory.
Can resonances occur in the photodissociation continuum of a diatomic molecule? The role of potential discontinuities
Authors: Tellinghuisen Joel
Published: October 2004

Continuum resonances are standard fare in the instructional literature for quantum mechanics, where they arise from the continuity conditions imposed on one-dimensional wavefunctions for piecewise-constant potential energy functions. Such resonance structure weakens progressively as the discontinuity in the potential is smoothed, showing that the structure is specifically attributable to the discontinuity. Since diatomic molecular potential energy curves seldom vary rapidly on the distance scale of the period of the wavefunction, such continuum resonances are not expected in absorption continua. A historically interesting prediction of such structure in the SchumannRunge continuum (B ← X) of O2 is attributed to the inadvertent incorporation of discontinuity in the B-state potential curve employed in the computations.Key words: quantum mechanics, continuum resonance, diatomic absorption, photodissociation continuum, numerical methods.
RKR-type inversion of the diatomic energy shifts due to breakdown of the BornOppenheimer approximation
Authors: Watson James KG
Published: October 2004

The principal effects of the breakdown of the BornOppenheimer approximation on the vibrationrotation energies of a diatomic molecule can be represented by the expectation values of terms to order (me/Mi) in the effective Hamiltonian, where me is the electron mass and Mi is the mass of atom i. This paper examines the possibility of inverting these expectation values to obtain the correction functions as functions of the internuclear distance r, using a generalization of the semiclassical RydbergKleinRees method. It is shown that the correction functions are not completely determinable from the inversion, and the form of the determinable combinations is obtained.Key words: diatomic molecules, vibrationrotation energies, isotope effects, BornOppenheimer breakdown, RydbergKleinRees method.
Vibrational spectra and electronvibration interactions of the naphthalene radical anion  Experimental and theoretical study
Authors: Torii Hajime , Ueno Yuko , Sakamoto Akira , Tasumi Mitsuo
Published: October 2004

Vibrational analysis is carried out for the radical anions of naphthalene-h8 and -d8. Their infrared (IR) spectra are observed in tetrahydrofuran by using a cell designed for IR measurements of unstable species. The vibrational force field and the IR intensities are calculated by the ab initio molecular orbital and density functional methods at various theoretical levels. As found in the cases of the radical cations of many polycyclic aromatic hydrocarbons (PAHs), a few strong IR bands with intensities of the order of 102 km mol1 are observed in the 1700900 cm1 region. These observed spectral features are well reproduced by the calculations at the CASSCF (complete active space self-consistent field) and B3LYP (Becke's three-parameter hybrid method using the LeeYangParr correlation functional) levels. The calculation at the B3LYP level gives a better fit between the observed and calculated absolute IR intensities. Normal modes and the origin of the strong IR intensities characteristic of the radical anions are discussed in terms of molecular symmetry coordinates and the dipole derivatives based on these coordinates. It is found that the IR intensities of the b2u modes below 2000 cm1 are dominated by the contribution from one molecular symmetry coordinate, in which the CC bonds in one ring stretch while those in the other ring shrink. The mechanism that gives rise to the strong IR intensity for this vibration is discussed by examining the changes in the electronic structure induced by this vibration.Key words: vibrational spectra, electronvibration interaction, naphthalene, radical anion.
Zero electron kinetic energy photoelectron and threshold photoionization spectroscopy of M-X(CH3)3 (M = Ga, In; X = P, As)
Authors: Li Shenggang , Rothschopf Gretchen K , Sohnlein Bradford R , Fuller Jason F , Yang Dong-Sheng
Published: October 2004

This paper presents pulsed-field ionization, zero electron kinetic energy (ZEKE) photoelectron and threshold photoionization spectra of M-X(CH3)3 (M = Ga, In; X = P, As). The ZEKE spectra exhibit well-resolved vibrational structures. A comparison with B3LYP calculations shows that the spectrum of In-P(CH3)3 arises from the 1A1 ← 2E transition and the spectra of Ga-P(CH3)3 and Ga-As(CH3)3 arise from transitions of a JahnTeller distorted doublet state to the 1A1 state. The intensities of the 1A12E transition in the indium species are described with the FranckCondon approximation, while the transitions in the gallium complexes are more complicated due to the dynamic JahnTeller effect. The adiabatic ionization potentials of Ga-P(CH3)3, In-P(CH3)3, and Ga-As(CH3)3 are 39 635, 38 930, and 40 322 cm1, respectively, and the ionization threshold of In-As(CH3)3 is ~39 550 cm1. The metalligand stretching frequencies are 143, 116, and 125 cm1 for Ga+-P, In+-P, and Ga+-As, respectively, and 96 cm1 for In-P. The intermolecular bending frequencies are 71, 65, and 42 cm1 for Ga+-P-C, In+-P-C, and Ga+-As-C, respectively, and 47 cm1 for In-P-C. In addition, ligand-based vibrational frequencies are determined for the CH3 wag, PC3 and AsC3 umbrella, and P-C stretching vibrations. Key words: ZEKE photoelectron, photoionization, DFT, galliumphosphine, galliumarsine, indiumphosphine, indiumarsine.
Spectroscopy of the XeC2 molecule in xenon, argon, and krypton matrices
Authors: Frankowski Marcin , Smith-Gicklhorn Alice M , Bondybey Vladimir E
Published: October 2004

A self-igniting DC-electric discharge of C2H2 in Xe (matrix gas) or C2H2 and Xe in Ar or Kr (matrix gas) is used to produce and study the XeC2 molecule in these various rare gases at 12 K. Unlike in Ar and Kr, the well-known electronic spectra of C2 is completely absent in a Xe matrix. This together with annealing experiments in Ar matrices indicate that ground state Xe and C2 react uniquely and without a barrier to form the XeC2 molecule. The IR-active C-C stretch of this compound is found to be close to the C-C stretching frequency of the C2 anion, in excellent agreement with our density functional theoretical (DFT) calculations, which yield a XeCC singlet species bent by 148.6° and with substantial charge separation approaching Xe+C2 and a notably short (2.107 Å) XeC bond. The spectra of the Xe13C12C, Xe12C13C, and Xe13C13C species are also obtained and the isotopic shifts are in excellent agreement with the DFT predictions, although not sufficient to distinguish a bent from a linear structure. Numerous broad absorptions centered near 423 nm (in Xe) are observed, which are clearly due to the XeC2 molecule. Laser-induced fluorescence studies reveal a near-IR emission likely due to XeC2 but not yet understood. Infrared spectra in the Xe matrix reveal also formation of the HXeCCH molecule.Key words: matrix-isolation spectroscopy, rare gas compounds, charge transfer compounds, xenoncarbon bonds.
Quantitative oscillator strengths for ionic fragmentation of C 1s and O 1s excited CO
Authors: Guerra A CO , Maciel J B , Turci C C , Bilodeau R C , Hitchcock A P
Published: October 2004

Ionic photofragmentation of carbon monoxide following carbon 1s and oxygen 1s excitation has been measured quantitatively with tuned synchrotron light and time-of-flight mass spectrometry using a WileyMcLaren apparatus modified with an additional ion lens for improved quantitative performance. The sensitivity of the apparatus to kinetic energy and angular distribution effects has been characterized for selected lens settings through ion trajectory simulations and experimental measurements. Three distinct modes of the added lens have been identified (focus, defocus, and maximum). The focus mode has the least sensitivity to details of the angular and ion kinetic energy distribution and, therefore, is the best mode for measuring quantitative partial ion and ion-pair yields. The defocus mode has the most sensitivity to angular and kinetic energy distributions and, therefore, is the mode that provides the most information about the kinematics of photofragmentation. Branching ratios for ion and ion-pair production in all positive ion fragmentation channels were recorded from 280 to 330 eV (C 1s) and from 520 to 570 eV (O 1s) in the "focus" mode. Quantitative oscillator strengths were derived by combining these branching ratios with absolute total ion yield spectra. The results are compared to literature values.Key words: CO, time-of-flight mass spectrometry, inner-shell excitation, quantitative oscillator strengths, cross sections.
The rotationally resolved electronic spectra of several conformers of 1-hexoxy and 1-heptoxy
Authors: Zu Lily , Liu Jinjun , Gopalakrishnan Sandhya , Miller Terry A
Published: October 2004

Laser-induced fluorescence excitation spectra of five vibronic bands of 1-hexoxy and three bands of 1-heptoxy have been recorded in a jet-cooled environment. Experimental values of rotational constants for both the [Formula: see text] and [Formula: see text] states and components of the spin-rotational tensor for the [Formula: see text] state were obtained by an analysis of the partially resolved rotational structure of the vibronic bands. Comparing these experimental results with quantum chemistry calculations, and using corresponding assignments of smaller alkoxy radicals as a guide, permitted unambiguous conformational assignments for the bands. The extension of similar assignments to larger alkoxy radicals is also discussed. Key words: electronic spectroscopy, organic radicals, combustion, atmospheric chemistry.
Threshold photoelectron spectroscopy of benzene up to 26.5 eV
Authors: Yencha Andrew J , Hall Richard I , Avaldi Lorenzo , Dawber Grant , McConkey Andrew G , MacDonald Michael A , King George C
Published: October 2004

The threshold photoelectron spectrum of benzene has been recorded up to 26.5 eV photon energy under high-resolution conditions using synchrotron radiation and employing the penetrating-field threshold electron collection method. By means of a direct comparative study with a recent HeI photoelectron spectrum of benzene of equally high resolution, numerous autoionization effects are observed in the formation of the ionic band systems of benzene in the outer valence ionization region in the threshold photoelectron spectrum. The Rydberg states responsible for these effects are identified. Autoionization does not appear to play a role in the formation of the two lowest-energy, inner-valence bands of C6H6+.Key words: threshold photoelectron spectroscopy, photoelectron spectroscopy, benzene, ionization, autoionization, Rydberg states.
Fluorine chemistry  Wittig based synthesis of volatile organofluorine compounds
Authors: Bhadury Pinaki S , Singh Sapna , Sharma Mamta , Palit Meehir , Jaiswal Devendra K
Published: October 2004

A simple and practical method has been developed for the synthesis and characterization of several interesting classes of volatile organofluorine compounds from fluorophosphonium salts via their in situ generated corresponding ylides. The fluorinated phosphonium ylides react with hexafluoroacetone in DMF to generate perfluoroisobutylene, whereas in the presence of bromine or iodine containing electrophiles, tetrafluoroethylene, perfluoro-2-butene, perfluorocyclobutane, and 1H-heptafluoropropane are obtained.Key words: difluoromethylene phosphonium ylides, perfluoroisobutylene, tetrafluoroethylene, perfluorocyclobutane, 1H-heptafluoropropane.
Is acyl migration to the aglycon avoidable in 2-acyl assisted glycosylation reactions?
Authors: Bérces Attila , Whitfield Dennis M , Nukada Tomoo , do Santos Z. Iwona , Obuchowska Agnes , Krepinsky Jiri J
Published: October 2004

This report unequivocally separates orthoester formation from acyl transfer for the first time and indicates possible routes to eliminate 2-O-acyl transfer during glycosylation reactions. Experimental evidence is shown that acyl transfer from 2-O-acyl-3,4,6-tri-O-benzyl-D-galactopyranose-derived glycosyl donors decreases in the order formyl > acetyl > pivaloyl. The 2-O-benzoyl derivatives are more variable, in some cases transferring easily, and in others not at all. Density functional theory (DFT) calculations of the structure and energetics of dioxolenium ion and related intermediates suggest that a proton transfer pathway from the nucleophile to O-2 provides an explanation for the observed trends. These DFT calculations of the proton transfer pathway support a mechanism in which a relay molecule is involved. Further DFT calculations used a constraint based on linear combinations of six bond lengths to establish the sequence of bond breaking and bond forming. The calculated anomeric carbon to former carbonyl oxygen bond that breaks during acyl transfer is the longest in the formyl case and shortest in those that exhibit little or no acyl transfer. Rotation about the aromatic to carbonyl PhC(=O) bond is different from the alkyl series. Analysis of this proposed TS led to the postulate that 2,6-substitution may hinder rotation even more. Thus, the 2,6-dimethylbenzoyl analogue was synthesized and it does not transfer directly or by rearrangement of its readily formed orthoester. DFT calculations suggested that 2,6-dimethoxybenzoyl should also not transfer easily. Experimentally, this proved to be the case and this new 2-O-acyl protecting group cleaves at 50 °C with a 1 mol/L solution of LiOH in methanol. Thus, a calculated transition state has led to a prototype of a protecting group that solves a major problem in oligosaccharide synthesis.Key words: glycosylation, carbohydrates, quantum chemistry, reaction mechanism, neighboring-group effects.
The 2003 CSC Pure or Applied Inorganic Chemistry Award Lecture Adventures in stable radical chemistry
Authors: Hicks Robin G
Published: October 2004

Stable radicals are of intense fundamental interest because they challenge conventional bonding paradigms, and they find a wide range of uses ranging from organic and polymer synthesis to biological and medicinal applications to materials science. Yet the directed synthesis and study of stable radicals for either fundamental or applied purposes are rarely pursued strategies. This Award Lecture describes my research group's efforts in exploratory and targeted research focusing on stable radical design.Key words: stable radicals, verdazyls, molecular magnetism.
A simple biomimetic protocol for the oxidation of alcohols with sodium hypochlorite in the presence of β-cyclodextrin in water
Authors: Surendra K , Krishnaveni N Srilakshmi , Rao K Rama
Published: October 2004

A simple and efficient protocol, which is inexpensive, convenient, clean, and facile, for oxidation of alcohols to carbonyl compounds has been developed using sodium hypochlorite in the presence of β-cyclodextrin with water as solvent. A series of alcohols were oxidized at room temperature in excellent yields.Key words: oxidation, alcohols, sodium hypochlorite, KBr, β-cyclodextrin, biomimetic, water.
Green preparation of quinoline derivatives through FeCl3·6H2O catalyzed Friedlander reaction in ionic liquids
Authors: Wang Jianji , Fan Xuesen , Zhang Xinying , Han Lijun
Published: October 2004

The preparation of substituted quinoline derivatives through a Friedlander condensation reaction utilizing the ionic liquid [bmim][BF4] as the reaction medium and iron chloride hexahydrate (FeCl3·6H2O) as a catalyst is described. The advantages in using this method include its environmental friendliness, simple operating process in both mild and neutral reaction conditions, and good yields.Key words: ionic liquid, Friedlander reaction, quinoline derivatives, green chemistry.
Gerhard Herzberg  A personal appreciation
Authors: Winnewisser G
Published: October 2004

Some important contributions of Gerhard Herzberg to molecular astronomy and the study of free radicals are highlighted and placed in the context of the history of spectroscopy.Key words: molecular spectroscopy, free radicals, methylene, interstellar lines.
An intercomparison of measured pressure-broadening and pressure-shifting parameters of water vapor
Authors: Gamache Robert R , Hartmann Jean-Michel
Published: October 2004

The present work is an intercomparison of experimental results on the pressure broadening and pressure shifting of water vapor absorption lines. The work focuses on application to the Earth's atmosphere; hence measurements of nitrogen, oxygen, air, and H2O as the buffer, or perturbing gas, were considered. The literature was searched and over 100 papers found. The data, measured half-widths, their temperature dependence, and the line shifts, were taken and databases created for each perturbing gas. The databases were reordered, grouping data for rovibrational transitions, and intercomparisons of the measurements made. Trends in the data, relationships between the data sets, and dependences on temperature and quantum numbers were investigated. The data were averaged and an estimated uncertainty determined. The averaged data sets are evaluated with respect to the need of the spectroscopic and remote sensing communities. Based on these studies, recommendations for new measurements are made.Key words: water vapor, half-widths, line shifts, temperature dependence of half-width.
Ultraviolet cavity ringdown spectra of 2-cyclohexen-1-one and its potential energy function and structure for the electronic ground state
Authors: Gilles Emily J , Choo Jaebum , Autrey Daniel , Rishard Mohamed , Drucker Stephen , Laane Jaan
Published: October 2004

The S1(n,π*) ← S0 cavity ringdown spectrum of 2-cyclohexen-1-one vapor has been recorded in the vicinity of the 000 band, which is at 26 089.1 cm1. Observation of hot bands in the spectrum has permitted the determination of several low-frequency fundamentals and overtones in the ground electronic state. The lowest two excited quantum states for the inversion vibration (v39) were found to be at 99.0 and 197.0 cm1. Together with previously published far-IR spectra and vapor-phase Raman spectra, the fundamental frequencies for v39, v38, and v37 have been determined. From observed v39 levels, the barrier to inversion has been determined experimentally to be 1900 ± 300 cm1, which is very different from values of 935 and 3379 cm1 previously reported from Raman and far-IR data, respectively. Density functional calculations carried out in this paper give a barrier value of 2090 cm-1 when the B3LYP/6-311+G(d,p) basis set is used.Key words: cavity ringdown spectra, 2-cyclohexen-1-one, Raman spectra, potential energy function, inversion barrier.
"Spectrum-only" assignment of core-penetrating and core-nonpenetrating Rydberg states of calcium monofluoride
Authors: Kay Jeffrey J , Byun Daniel S , Clevenger Jason O , Jiang Xing , Petrović Vladimir S , Seiler Robert , Barchi Jonathan R , Merer Anthony J , Field Robert W
Published: October 2004

Rydberg states of calcium monofluoride in the n* = 1720 region have been observed by ionization-detected opticaloptical double-resonance spectroscopy via the D2Σ+ v = 1 intermediate state. All members of the six core-penetrating Rydberg series in the n* = 1720 region and several components of the 17f and 17g core-nonpenetrating Rydberg states have been assigned. While the assignment of core-penetrating Rydberg states is straightforward without use of an effective Hamiltonian model, "spectrum-only" assignment of core-nonpenetrating states is complicated because strong l-uncoupling causes the core-nonpenetrating states to evolve rapidly from Hund's case (b) to Hund's case (d) coupling. We describe "spectrum-only" assignment procedures, developed in the spirit of Gerhard Herzberg, that can be used to assign opticaloptical double-resonance spectra of core-penetrating and core-nonpenetrating Rydberg states using only information contained in the spectrum rather than predictions derived from an effective Hamiltonian model. The ambiguities that arise in the assignment of each class of states are discussed in detail.Key words: CaF, electric quadrupole moment, Rydberg states, laser spectroscopy.
Probing of the hot-band excitations in the photodissociation of OCS at 288 nm by DC slice imaging
Authors: Kim Myung Hwa , Li Wen , Lee Suk Kyoung , Suits Arthur G
Published: October 2004

The photodissociation dynamics of OCS at 288 nm has been investigated using the DC (direct current) slice imaging technique, which is a recently developed high-resolution "slicing" approach that directly measures the central slice of the photofragment distribution in imaging experiments. By analyzing a DC sliced image of S(1D2) photofragments we observe dissociation originating from OCS molecules excited up to v2 = 4 in the molecular beam. The measured translational energy distribution was used to determine the branching ratio for the contribution from each initial bending state (0 v2 0) of OCS and relative photodissociation cross section ratios compared to v2 = 1. Large negative anisotropy parameters determined as a function of the S(1D2) fragment recoil speed indicate that the photodissociation of OCS at 288 nm occurs exclusively from the 11A′′(1Σ) bending excited potential surface that can be accessed through a perpendicular transition.Key words: DC slicing imaging, OCS, photodissociation, hot-band excitation.
High-resolution vacuum ultraviolet laser spectroscopy of the C 0+u ← X 0+g transition of Xe2
Authors: Wüest A , Hollenstein U , de Bruin K G , Merkt F
Published: October 2004

Rotationally resolved (1 + 1′), resonance-enhanced, two-photon ionization spectra of the C 0+u ← X 0+g transition of several isotopomers of Xe2 have been recorded. Rotational constants have been determined for the v′ = 1426 levels of the C 0+u Rydberg state and the v′′ = 0 and 1 levels of the X 0+g ground state, and band origins have been determined with an absolute accuracy of 0.015 cm1 for the transitions to the v′ = 1426 levels of the C 0+u state of the 129Xe2, 129Xe132Xe, and 131Xe136Xe isotopomers. The equilibrium internuclear separation of the X 0+g ground state (Re = 4.3773(49) Å) was determined from the rotational constants of the v′′ = 0 and 1 levels. The analysis of the isotopic shifts of the band origins enabled the confirmation of the absolute numbering of the vibrational levels of the C 0+u state determined by Lipson et al. (R.H. Lipson, P.E. Larocque, and B.P. Stoicheff. J. Chem. Phys. 82, 4470 (1985)). A semiempirical interaction potential for the X 0+g ground state was derived in a nonlinear fitting procedure using the present spectroscopic results, the positions of the v′′ = 29 levels determined by Freeman et al. (D.E. Freeman, K. Yoshino, and Y. Tanaka. J. Chem. Phys. 61, 4880 (1974)) and experimental values for the second virial coefficient. The interaction potential is similar to previous semiempirical potentials but the dissociation energy (De = (196.1 ± 1.1) cm1) differs from the value of 183.1 cm1 determined in the latest ab initio calculation (P. Slavíček, R. Kalus, P. Paka, I. Odvárková, P. Hobza, and A. Malijevský. J. Chem. Phys. 119, 2102 (2003)).

Key words: high-resolution vacuum ultraviolet laser spectroscopy, rare gas dimers and their cations, photoionisation, Xe2, rotationally resolved electronic spectrum.
Line strength factors for E,F1Σ+g(v′ = 0, J′ = J′′)  X1Σ+g (v′′, J′′) (2 + 1) REMPI transitions in molecular hydrogen
Authors: Pomerantz Andrew E , Ausfelder Florian , Zare Richard N , Huo Winifred M
Published: October 2004

Experimentally and theoretically determined line strengths are presented for E,F1Σ+g(v′ = 0, J′ = J′′)  X1Σ+g (v′′, J′′) (2 + 1) REMPI transitions in H2, HD, and D2. The experimental technique employs a hot filament source of internally excited hydrogen that allows experimental determination of line strengths for the low rotational states of highly excited vibrational manifolds (v′′ ≤ 4). The line strengths are found to depend only weakly on J′′ for the states measured here, and theoretical results indicate that the line strengths depend strongly on v′′. These values are combined with previously measured and calculated line strengths for these transitions (K.-D. Rinnen, M.A. Buntine, D.A.V. Kliner, R.N. Zare, and W.M. Huo. J. Chem. Phys. 95, 214 (1991)), resulting in a more complete compilation of REMPI line strengths for molecular hydrogen. Key words: hydrogen, spectroscopy, REMPI, line strength, multiphoton.
Chemical adsorption of salicylate on silver - A systematic approach to the interpretation of surface-enhanced vibrational spectra
Authors: Goulet P J.G , Aroca R F
Published: October 2004

In this work, surface-enhanced vibrational spectroscopy and normal vibrational spectroscopy as well as density functional theory (DFT) computational methods have been employed to investigate the nature of the chemical adsorption and orientation of the surface species generated from salicylic acid at silver surfaces. The structure of salicylic acid and its IR and Raman spectra are determined at the B3LYP/6-311+G(d,p) level of theory. These results are used in the assignment of the vibrational spectra. Surface-enhanced Raman scattering (SERS) spectra obtained from silver island films thinly coated with salicylic acid confirm chemical adsorption on the Ag nanostructures. To probe the nature of this surface complex, the optimized geometries and IR and Raman spectra of two model salicylate-silver complexes (Ag1 and Ag2) were calculated at the B3LYP/Lanl2DZ level of theory. It was found that good agreement exists between experimentally observed SERS spectra and the simulated SERS spectra of a complex with the salicylate monoanion bound to a Ag+ ion through its carboxylate group (Ag1). The carboxylate silver salt of salicylic acid (essentially the Ag1 complex) was also prepared, and its IR and Raman spectra were recorded for comparison with the surface-enhanced vibrational spectra. These results, along with the application of surface selection rules, suggest that salicylic acid is deprotonated at silver surfaces, interacting through its carboxylate group alone, and is preferentially in a tilted head-on orientation.Key words: chemisorption, salicylic acid, silver, density functional theory, surface-enhanced Raman scattering, reflection-absorption IR spectroscopy, surface-enhanced IR absorption.
A study of the A2Π/B2Σ+  X2Σ+ band systems of calcium monohydride (CaH) using a supersonic molecular beam source and laser-induced fluorescence detection
Authors: Steimle T C , Gengler Jamie , Chen Jinhai
Published: October 2004

The high-resolution laser-induced fluorescence spectrum of a molecular beam sample of calcium monohydride (CaH) in the region of the strongly overlapped (1,0) A2Π  X2Σ+ and (0,0) B2Σ+   X2Σ+ band systems near 630 nm and the (0,0) A2Π   X2Σ+ band system near 690 nm have been recorded and analyzed. The spectral features exhibit a small splitting that is attributed to proton magnetic hyperfine interaction in the X2Σ+ (v = 0) state. The energy levels of the A2Π(v = 0) vibronic state were modeled using a traditional "effective" Hamiltonian approach, whereas those for the interacting A2Π(v = 1)/B2Σ+(v = 0) vibronic levels were modeled by augmenting the traditional effective Hamiltonian with terms to account for local perturbations. An interpretation of the field-free parameters is presented.Key words: calcium monohydride, molecular beam, fluorescence.
SiO as a chemical signature of outflows from bright, compact sources in MSX IR-dark clouds
Authors: Feldman P A , Redman R O , Avery L W , Francesco J Di , Fiege J D , Carey S J , Wyrowski F
Published: October 2004

The line profiles of dense cores in infrared-dark clouds indicate the presence of young stellar objects (YSOs), but the youth of the YSOs and the large distances to the clouds make it difficult to distinguish the outflows that normally accompany star formation from turbulence within the cloud. We report here the first unambiguous identification of a bipolar outflow from a young stellar object (YSO) in an infrared-dark cloud, using observations of SiO to distinguish the relatively small amounts of gas in the outflow from the rest of the ambient cloud. Key words: infrared-dark clouds, star formation, bipolar outflows, SiO, G81.56+0.10.
Attosecond molecular spectroscopy  The one-electron H2+ system
Authors: Bandrauk André D , Nguyen Hong Shon
Published: October 2004

Numerical solutions of the time-dependent Schrödinger equation for a 1-D model non-BornOppenheimer H2+ are used to illustrate the nonlinear, nonperturbative response of molecules to intense (I ≥ 1013 W/cm2), ultrashort (t < 10 fs) laser pulses. Molecular high-order harmonic generation (MHOHG) is shown to be an example of such response, and the resulting nonlinear photon emission spectrum is shown to lead to the synthesis of single attosecond (1018 s) pulses. Application of such ultrashort pulses to the H2+ system results in localized electron wave packets whose motion can be detected by asymmetry in the photoelectron spectrum generated by a subsequent probe attosecond pulse, thus leading to measurement of electron motion in molecules on an attosecond time scale.

Key words: attosecond spectroscopy, attosecond photoionization.
TMAH-pyrolysis  gas chromatography  mass spectrometry analysis of residual lignin changes in softwood kraft pulp during oxygen delignification
Authors: Fu Shiyu , Lucia Lucian A
Published: October 2004

The residual lignins from pulps and effluent lignins from oxygen delignification effluents were characterized using pyrolysis  gas chromatography  mass spectrometry in the presence of tetramethylammonium hydroxide. The results indicated that oxidation under alkali oxygen conditions can induce fragmentation in lignin and produce more acid groups, but the lignin maintains most of its C6C3 units. Oxygen delignification also led to a decrease in diphenyl structures in the residual lignin and an enrichment in concentration of lignin carbohydrate complex structures.Key words: residual lignin, pyrolysis, oxygen delignification.
Studies on the two-photon absorption properties of trigonal dehydrobenzo[18]annulenes
Authors: Zhou Xin , Ren Ai-Min , Feng Ji-Kang , Liu Xiao-Juan
Published: October 2004

The one-photon and two-photon absorption properties of donoracceptor substituted dehydrobenzo[18]annulenes were determined by using density functional theory and ZINDO methods. The macrocycle containing C2v symmetry exhibited the largest TPA cross-section value of 3376 × 1050 cm4 s/photon. The calculated results indicate that the TPA response in the whole molecule comes from the contribution of that in the every side in the trigon. It is notable that the magnitudes of the transition dipole moment from the virtual intermediate state to the TPA final state and the dipole moment difference between the ground state and the virtual intermediate state play important roles in increasing the TPA cross-section value. This series of molecules can circumvent the trade-off between efficiency and transparency, and they provide a promising direction for the further development of novel two-dimensional molecules with such properties.Key words: two-photon absorption, ZINDO, sum-over-states, dehydrobenzo[18] annulenes, transparency.
Identification of glycerophospholipids in rapeseed, olive, almond, and sunflower oils by LCMS and LCMSMS
Authors: Boukhchina Sadok , Sebai Khaled , Cherif Ammar , Kallel Habib , Mayer Paul M
Published: October 2004

HPLC employing a thermostatted Lichrospher 100 diol column was used to separate mixtures of glycerophospholipids of rapeseed, olive, almond, and sunflower oils. Elution was performed with a binary gradient of two mixed solvents A: hexane  isopropanol  acetic acid  triethylamine (82:17:1.0:0.08 v/v/v/v) and B: isopropanol  water  acetic acid  triethylamine (85:14:1.0:0.08 v/v/v/v). The LC effluent was directly introduced into the mass spectrometer through an electrospray capillary. Information about the fatty acid composition of each glycerophos pho lipid class was given by tandem mass spectrometry (MSMS). These techniques permitted a rapid separation and identification of complex mixtures of glycerophospholipids. The relative abundance of each lipid class in each oil was also determined. The resulting glycerophospholipid signature may provide an efficient means of identifying oil origin and possible adulteration.Key words: glycerophospholipids, vegetable oils, tandem mass spectrometry, LCMS.
A one-pot synthesis and X-ray crystallographic and computational analyses of methyl-2,4-dimethoxysalicylate  a potential anti-tumour agent
Authors: Dabbagh Hossein A , Noroozi-Pesyan Nader , Patrick Brian O , James Brian R
Published: October 2004

The thermal decarboxylation of 2-methoxycarbonyl-5-(4′-nitrophen-oxy)tetrazole (1a) with the electron-rich, aromatic compounds (anisole, N,N-dimethylaniline, 1,4-dimethoxybenzene, and 1,3,5-trimethoxybenzene), neat or in polar solvents (DMSO, DMF, and CH3CN), is investigated. The solid phase thermal decomposition of a mixture of 1a, 1,3,5-trimethoxybenzene, and a Lewis acid (AlCl3) produces methyl-2,4-dimethoxysalicylate (8) in good yield, instead of the expected 2,4,6-trimethoxybenzoic acid. The X-ray structure of 8 shows intramolecular hydrogen bonds between the carbonyl oxygen and hydrogens of Me and OH groups. A measured pKa value of 6.8 compares well with a value of 6.4 estimated using the [C=O···H···O] hydrogen bond distances.Key words: antitumor, novel synthesis, X-ray structure, hydrogen bonds, computational analysis.
A biogeochemical analysis of the Pocono till barrens and adjacent hardwood forest underlain by Wisconsinan and Illinoian till in northeastern Pennsylvania
Authors: Wibiralske Anne W , Latham Roger Earl , Johnson Arthur H
Published: October 2004

We assessed soil and vegetation nutrient capital in the landscape mosaic of till barrens and hardwood forests on the Pocono Plateau in northeastern Pennsylvania. These shrublands, which contain an unusual abundance of rare species, occur primarily on Illinoian-aged glacial till, though some patches grow on Wisconsinan till. We hypothesized that barrens soil and vegetation contain smaller quantities of nutrients than forest soil and vegetation, and under the same vegetation, Illinoian till soils have a smaller nutrient content than Wisconsinan till soils. We measured pH, total C and N, and exchangeable Ca, Mg, K, and Al content of the soils and determined C, N, Ca, Mg, K, and P content of the vegetation. Litter and soil organic matter in the barrens have a higher C/N ratio than the forest. The Illinoian barrens Oa horizon is thicker and contains a greater quantity of exchangeable mineral nutrients than the other Oa horizons. Differences in vegetation nutrient capital strongly mirror differences in biomass. Our results show no strong association of parent material with soil or vegetation nutrient capital. Instead, they suggest that plant community characteristics, not soil nutrient availability, shape the landscape pattern of barrens and forest, particularly plant-driven positive feedbacks primarily involving fire frequency.
The accuracy of estimating individual tree variables with airborne laser scanning in a boreal nature reserve
Authors: Maltamo M , Mustonen K , Hyyppä J , Pitkänen J , Yu X
Published: October 2004

This study examines the ability of high-density laser scanning to produce single-tree estimates in mixed stands of heterogeneous structure. Individual trees were detected from a constructed digital canopy height model by locating local maxima of the height values. The reference material comprised accurately measured field data for 10 mapped sample plots containing Norway spruce (Picea abies (L.) Karst.), Scots pine (Pinus sylvestris L.), and different birches. To verify the accuracy of height measurements of single trees in more detail, the height of 29 Scots pine trees and their annual shoots of the last few years was carefully measured with a tacheometer and a glass fibre rod. The considered variables were the proportion of detected trees and tree height. As more than 80% of the dominant trees were detected, the results indicated that laser scanning can accurately describe the trees of the dominant tree layer. Because of the dense understorey tree layer in most of the sample plots, about 40% of all trees were detected. On the plot level, the stand structure affected the accuracy of the results considerably. The scanning-based tree height was most accurate for Norway spruce and least accurate for birches. The height of the separately measured 29 Scots pine trees was obtained with an accuracy of ±50 cm or better.
A restricted Leontief profit function model of the Canadian lumber and chip industry: potential impacts of US countervail and Kyoto ratification
Authors: Williamson T , Hauer G , Luckert M K
Published: October 2004

Estimation of output supplies and factor demands with a range of functional forms provides a basis for bounding possible supply responses to exogenous shocks. No prior study, to our knowledge, has used a generalized Leontief functional form to estimate lumber and chip supply responses in Canada. The own price lumber supply elasticities estimated from the restricted Leontief profit functional form used in this study are lower than those presented in most other studies, while the lumber supply response with respect to roundwood price change is somewhat higher than some studies. We simulate the impacts of current US countervail processes on Canadian lumber supply. The simulated responses to duties might be considered to be conservative estimates, while the lumber supply responses to roundwood price increases could be on the high end of expected responses. Estimation of profit and supply functions indicates that rather than being a distinct production decision, chip supply follows lumber supply. The supply responses of chips and lumber to the various combinations of duty, roundwood price increases, and energy price increases indicate a number of patterns. First, if Kyoto policies increase energy prices (up to 10%), these changes are not likely to have a large impact on lumber and chip production. Second, British Columbia and Quebec tend to have lumber and chip supplies that are more sensitive to duties and increased roundwood prices than Ontario. Third, Quebec is more sensitive to roundwood price increases, while British Columbia is more sensitive to the effects of duties.