: The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields

This paper studies the impact of ambiguity and ambiguity aversion on equilibrium asset prices and portfolio holdings in competitive financial markets. It argues that attitudes toward ambiguity are heterogeneous across the population, just as attitudes toward risk are heterogeneous across the population, but that heterogeneity of attitudes toward ambiguity has different implications than heterogeneity of attitudes toward risk. In particular, when some state probabilities are not known, agents who are sufficiently ambiguity averse find open sets of prices for which they refuse to hold an ambiguous portfolio. This suggests a different cross-section of portfolio choices, a wider range of state price/probability ratios and different rankings of state price/probability ratios than would be predicted if state probabilities were known. Experiments confirm all of these suggestions. Our findings contradict the claim that investors who have cognitive biases do not affect prices because they are infra-marginal: ambiguity averse investors have an indirect effect on prices because they change the per-capita amount of risk that is to be shared among the marginal investors. Our experimental data also suggest a positive correlation between risk aversion and ambiguity aversion that might explain the “value effect” in historical data.

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Theory and Experiment

Advances and challenges in laminar flame experiments and implications for combustion chemistry

An overview is given of recent developments in laser diagnostic methods for the quantitative measurement of trace species concentrations and, in conjunction, of temperature in combustion systems. After a short introduction illustrating some experiments from the pre-laser era, the article presents typical applications and discusses advantages and limitations of laser techniques including laser absorption, linear, saturated, predissociative and multi-photon-excited laser-induced fluorescence (LIF), resonance-enhanced multiphoton ionization (REMPI), electronically resonant coherent anti-Stokes Raman scattering (resonance CARS), degenerate four-wave mixing (DFWM) and amplified spontaneous emission (ASE). Recent trends including two-dimensional imaging, multi-species detection and high-pressure applications will also be discussed. Throughout the article, an attempt is made to present typical results from a large portion of the relevant technical literature. A concluding section gives a short summary of the current status and comments on the perspectives for further research.

Laser Techniques for the Quantitative Detection of Reactive Intermediates

Laser techniques for the quantitative detection of reactive intermediates in combustion systems

Argon clusters were produced in a free supersonic molecular beam expansion of pure argon at room temperature and the photoionization efficiency curves of the trimer through hexamer were measured in the wavelength regions from threshold to 700 A. A study of the Ar+3 photoionization efficiency curve as a function of nozzle stagnation pressure shows that fragmentation of heavier clusters can dominate the spectrum, even near threshold, and even when the nozzle conditions are such that the Ar+4 intensity is only a small fraction of the Ar+3 intensity. The Ar+3 photoionization efficiency curve, obtained using nozzle stagnation conditions such that no heavier ions were detected, exhibits several broad peaks near threshold which show similarities to bands of the dimer. At high nozzle stagnation pressures, the photoionization efficiency curves for Ar+3 to Ar+6 are nearly identical due to the effects of fragmentation. These spectra exhibit two very broad features which are similar to features observed in the solid....

Photoionization of argon clusters

Photoionization of excited molecular states. H2 C 1Πu

We report measurements of photoelectron spectra of an electronically excited state of H2 (B 1Σ+u) in selected vibrational and rotational levels The excited state was prepared by resonant three photon excitation of H2 X 1Σ+g, v=0,  J=3 and subsequently was ionized by a single additional photon Partially resolved rotational structure is observed in the photoelectron spectra and is discussed in terms of the selection rules for direct photoionization and the partial wave composition of the ejected photoelectrons An additional peak is observed in the spectra, which is tentatively interpreted as arising from photoionization of H*(n=2) formed by photodissociation of H2 in the B 1Σ+u state

Resonant multiphoton ionization of H2 via the B 1Σ+u, v=7, J=2 and 4 levels with photoelectron energy analysis

The absolute photoionization cross-section of the methyl radical has been measured using two completely independent methods. The CH3 photoionization cross-section was determined relative to that of acetone and methyl vinyl ketone at photon energies of 10.2 and 11.0 eV by using a pulsed laser-photolysis/time-resolved synchrotron photoionization mass spectrometry method. The time-resolved depletion of the acetone or methyl vinyl ketone precursor and the production of methyl radicals following 193 nm photolysis are monitored simultaneously by using time-resolved synchrotron photoionization mass spectrometry. Comparison of the initial methyl signal with the decrease in precursor signal, in combination with previously measured absolute photoionization cross-sections of the precursors, yields the absolute photoionization cross-section of the methyl radical; σCH3(10.2 eV) = (5.7 ± 0.9) × 10−18 cm2 and σCH3(11.0 eV) = (6.0 ± 2.0) × 10−18 cm2. The photoionization cross-section for vinyl radical determined by photo...

Absolute Photoionization Cross-Section of the Methyl Radical†

Double‐resonance excitation via the A 1Au state is used to record zero‐kinetic‐energy photoelectron spectra of acetylene. The analysis of these spectra leads to an improved value of 91 952±2 cm−1 for the adiabatic ionization potential to the C2H2+ X 2Πu ionic ground state. Because the A 1Au intermediate state has a trans‐bent geometry, transitions from it readily populate the trans‐bending vibration of the ground state ion, leading to new information about this mode and its Renner–Teller interactions. The relative intensities of the Renner–Teller components and of the rotational structure within each component also provide information on the dynamics of the photoionization process.

Zero‐kinetic‐energy photoelectron spectroscopy from the Ã 1Au state of acetylene: Renner–Teller interactions in the trans‐bending vibration of C2H+2X̃ 2Πu

Stephen T. Pratt

Papers

Photoionization of argon clusters

Photoionization of excited molecular states. H2 C 1Πu

Resonant multiphoton ionization of H2 via the B 1Σ+u, v=7, J=2 and 4 levels with photoelectron energy analysis

Absolute Photoionization Cross-Section of the Methyl Radical†

Zero‐kinetic‐energy photoelectron spectroscopy from the Ã 1Au state of acetylene: Renner–Teller interactions in the trans‐bending vibration of C2H+2X̃ 2Πu