Competing Dispersive Interactions: From Small Energy Differences to Large Structural Effects in Methyl Jasmonate and Zingerone.

Modern structural studies of biologically relevant molecules require an exhaustive interplay between experiment and theory. In this work, we present two examples where a poor choice of the theoretical method led to a misinterpretation of experimental results. We do that by performing a rotational spectroscopy study on two large and flexible biomolecules: methyl jasmonate and zingerone.

Tackling the mortality from long-term exposure to outdoor air pollution in megacities: Lessons from the Greater Cairo case study.

Objective: The poor outdoor air quality in megacities of the developing world and its impact on health is a matter of concern for both the local populations and the decision-makers. The objective of this work is to quantify the mortality attributable to long-term exposure to PM2.5, NO, and O in Greater Cairo (Egypt).

The Essential Role for Laboratory Studies in Atmospheric Chemistry.

Laboratory studies of atmospheric chemistry characterize the nature of atmospherically relevant processes down to the molecular level, providing fundamental information used to assess how human activities drive environmental phenomena such as climate change, urban air pollution, ecosystem health, indoor air quality, and stratospheric ozone depletion. Laboratory studies have a central role in addressing the incomplete fundamental knowledge of atmospheric chemistry. This article highlights the evolving science needs for this community and emphasizes how our knowledge is far from complete, hindering our ability to predict the future state of our atmosphere and to respond to emerging global environmental change issues.

Identifying Cytosine-Specific Isomers via High-Accuracy Single Photon Ionization.

Biological entities, such as DNA bases or proteins, possess numerous tautomers and isomers that lie close in energy, making the experimental characterization of a unique tautomer challenging. We apply VUV synchrotron-based experiments combined with state-of-the-art ab initio methodology to determine the adiabatic ionization energies (AIEs) of specific gas-phase cytosine tautomers produced in a molecular beam. The structures and energetics of neutral and cationic cytosine tautomers were determined using explicitly correlated methods.

Enhanced Volatile Organic Compounds emissions and organic aerosol mass increase the oligomer content of atmospheric aerosols.

Secondary organic aerosol (SOA) accounts for a dominant fraction of the submicron atmospheric particle mass, but knowledge of the formation, composition and climate effects of SOA is incomplete and limits our understanding of overall aerosol effects in the atmosphere. Organic oligomers were discovered as dominant components in SOA over a decade ago in laboratory experiments and have since been proposed to play a dominant role in many aerosol processes. However, it remains unclear whether oligomers are relevant under ambient atmospheric conditions because they are often not clearly observed in field samples.

Torsion-rotation-vibration effects in the ground and first excited states of methacrolein, a major atmospheric oxidation product of isoprene.

Methacrolein is a major oxidation product of isoprene emitted in the troposphere. New spectroscopy information is provided with the aim to allow unambiguous identification of this complex molecule, characterized by a large amplitude motion associated with the methyl top. State-of-the-art millimeter-wave spectroscopy experiments coupled to quantum chemical calculations have been performed.

Interplay of experiment and theory: high resolution infrared spectrum and accurate equilibrium structure of BF2OH.

The high-resolution Fourier transform infrared (FTIR) spectrum of (11)BF2OH (difluoroboric acid) is analyzed taking into account numerous interactions. The ν1, ν2 and ν3 infrared bands are analyzed for the first time, whereas the parameters of the 6(1), 7(1), 8(1) and 9(1) states and for the 4(1) and 9(2) interacting states are redetermined. These results are used to check the quality of the ab initio force field.

Spin-torsion effects in the hyperfine structure of methanol.

The magnetic hyperfine structure of the non-rigid methanol molecule is investigated experimentally and theoretically. 12 hyperfine patterns are recorded using molecular beam microwave spectrometers. These patterns, along with previously recorded ones, are analyzed in an attempt to evidence the effects of the magnetic spin-torsion coupling due to the large amplitude internal rotation of the methyl group [J.

Theoretical and Experimental Photoelectron Spectroscopy Characterization of the Ground State of Thymine Cation.

We report on the vibronic structure of the ground state X̃(2)A″ of the thymine cation, which has been measured using a threshold photoelectron photoion coincidence technique and vacuum ultraviolet synchrotron radiation. The threshold photoelectron spectrum, recorded over ∼0.7 eV above the ionization potential (i.

VUV photoionization and dissociative photoionization of the prebiotic molecule acetyl cyanide: theory and experiment.

The present combined theoretical and experimental investigation concerns the single photoionization of gas-phase acetyl cyanide and the fragmentation pathways of the resulting cation. Acetyl cyanide (AC) is inspired from both the chemistry of cyanoacetylene and the Strecker reaction which are thought to be at the origin of medium sized prebiotic molecules in the interstellar medium. AC can be formed by reaction from cyanoacetylene and water but also from acetaldehyde and HCN or the corresponding radicals.

Photoionization spectroscopy of nucleobases and analogues in the gas phase using synchrotron radiation as excitation light source.

We review here the photoionization and photoelectron spectroscopy of the gas phase nucleic acid bases adenine, thymine, uracil, cytosine, and guanine, as well as the three base analogues 2-hydroxyisoquinoline, 2-pyridone, and δ-valerolactam in the vacuum ultraviolet (VUV) spectral regime. The chapter focuses on experimental work performed with VUV synchrotron radiation and related ab initio quantum chemical calculations of higher excited states beyond the ionization energy. After a general part, where experimental and theoretical techniques are described in detail, key results are presented by order of growing complexity in the spectra of the molecules.

Analysis of the microwave, terahertz, and far infrared spectra of monodeuterated methanol CH2DOH up to J = 26, K = 11, and o(1).

The first theoretical approach aimed at accounting for the energy levels of a non-rigid molecule displaying asymmetric-top asymmetric-frame internal rotation is developed. It is applied to a line position analysis of the high-resolution spectrum of the non-rigid CH2DOH molecule and allows us to carry out a global analysis of a data set consisting of already available data and of microwave and far infrared transitions measured in this work. The analysis is restricted to the three lowest lying torsional levels (e0, e1, and o1), to K ⩽ 11, and to J ⩽ 26.

Line broadening of confined CO gas: from molecule-wall to molecule-molecule collisions with pressure.

The infrared absorption in the fundamental band of CO gas confined in porous silica xerogel has been recorded at room temperature for pressures between about 5 and 920 hPa using a high resolution Fourier transform spectrometer. The widths of individual lines are determined from fits of measured spectra and compared with ab initio predictions obtained from requantized classical molecular dynamics simulations. Good agreement is obtained from the low pressure regime where the line shapes are governed by molecule-wall collisions to high pressures where the influence of molecule-molecule interactions dominates.

Coupled large amplitude motions: a case study of the dimethylbenzaldehyde isomers.

The microwave spectra of the 3,4- (syn and anti), 2,5- (syn), and 3,5-dimethylbenzaldehyde (DMBA) molecules have been recorded for the first time in the 2-26.5 GHz frequency range, using the high resolution COBRA-FTMW spectrometer in Hannover. The experimental assignments and fits are supplemented by ab initio quantum chemical calculations of the conformational energy landscape and dipole moment components.

Analysis of the torsional spectrum of monodeuterated methanol CH2DOH.

An analysis of the torsional spectrum of monodeuterated methanol CH(2)DOH is presented. Twenty nine torsional subbands have been assigned in the 20-800 cm(-1) region. The newly assigned subbands and those already available in the literature were analyzed with a theoretical approach accounting for internal rotation of an asymmetrical CH(2)D methyl group.

Early stage of weathering of medieval-like potash-lime model glass: evaluation of key factors.

Purpose: Throughout history, a consequent part of the medieval stained glass windows have been lost, mostly because of deliberate or accidental mechanic destruction during war or revolution, but, in some cases, did not withstand the test of time simply because of their low durability. Indeed, the glasses that remain nowadays are for many in a poor state of conservation and are heavily deteriorated. Under general exposure conditions, stained glass windows undergo different kinds of weathering processes that modify their optical properties, chemistry, and structure: congruent dissolution, leaching, and particle deposition (the combination of those two leading together to the formation of neocrystallisations and eventually crusts).