Predicting Attitudes toward Press- and Speech Freedom across the U.S.A.: A Test of Climato-Economic, Parasite Stress, and Life History Theories

<div><p>National surveys reveal notable individual differences in U.S. citizens’ attitudes toward freedom of expression, including freedom of the press and speech. Recent theoretical developments and empirical findings suggest that ecological factors impact censorship attitudes in addition to individual difference variables (e.g., education, conservatism), but no research has compared the explanatory power of prominent ecological theories. This study tested climato-economic, parasite stress, and life history theories using four measures of attitudes toward censoring the press and offensive speech obtained from two national surveys in the U.S.A. Neither climate demands nor its interaction with state wealth—two key variables for climato-economic theory—predicted any of the four outcome measures. Interstate parasite stress significantly predicted two, with a marginally significant effect on the third, but the effects became non-significant when the analyses were stratified for race (as a control for extrinsic risks). Teenage birth rates (a proxy of human life history) significantly predicted attitudes toward press freedom during wartime, but the effect was the opposite of what life history theory predicted. While none of the three theories provided a fully successful explanation of individual differences in attitudes toward freedom of expression, parasite stress and life history theories do show potentials. Future research should continue examining the impact of these ecological factors on human psychology by further specifying the mechanisms and developing better measures for those theories.</p></div

Isomerization as a Key Path to Molecular Products in the Gas-Phase Decomposition of Halons

The decomposition of halons remains controversial concerning the branching between radical and molecular products. The latter channel, where it has been found, is presumed to occur via a constrained symmetric multicenter transition state. Isomerization pathways in the gas-phase chemistry of halons have rarely been considered, despite the fact that the iso-halons, which feature a halogen−halogen bond, are widely recognized as important reactive intermediates in condensed phases. In this Letter, detailed calculations and modeling of the unimolecular decomposition of several important halons, including CF₂Cl₂, CF₂Br₂, and CHBr₃, reveal that isomerization is a key pathway to molecular products. This path is important for both halons and their primary radicals as the barrier to isomerization in these compounds is typically isoenergetic with the threshold for bond fission

Purpose and example items of the four tests as well as the surveys from which the items were drawn.

<p>Purpose and example items of the four tests as well as the surveys from which the items were drawn.</p

Case of the Missing Isomer: Pathways for Molecular Elimination in the Photoinduced Decomposition of 1,1-Dibromoethane

We report an experimental and computational study of the photodecomposition pathways of a prototypical gem-dihalide, 1,1-dibromoethane (1,1-EDB), in the condensed phase. Following photolysis of the matrix isolated parent compound in Ar at 5 K, photoproducts are observed corresponding to Br₂ elimination (+ C₂H₄ or C₂H₂) and HBr elimination (+ vinyl bromide). The elimination products are observed in the matrix as complexes. In contrast to our recent studies of the photolysis of matrix isolated polyhalomethanes, no evidence for the iso-1,1-EDB species is found, although studies of the matrix isolated 1,1-dibromo-2,2,2-trifluoroethane analogue show that the isomer is the dominant photoproduct. These results are examined in the light of theoretical studies that have characterized in detail the 1,1-EDB potential energy surface (PES). For Br₂ elimination, a pathway from the isomer on the singlet PES is found which involves a simultaneous Br₂ loss with 1,2-hydrogen shift; this pathway lies lower in energy than a concerted three-center elimination from the parent 1,1-EDB. For HBr elimination, our previous theoretical studies [Kalume, A.; George, L.; Cunningham, N.; Reid, S. A. <i>Chem. Phys. Lett.</i> <b>2013</b>, <i>556</i>, 35–38] have demonstrated the existence of concerted (single-step) and sequential pathways that involve coupled proton and electron transfer, with the sequential pathway involving the isomer as an intermediate. Here, more extensive computational results argue against a simple radical abstraction pathway for this process, and we compare experimental and computational results to prior results from the photolysis of the structural isomer, 1,2-EDB. These steady-state experiments set the stage for ultrafast studies of the dynamics of this system, which will be important in unraveling the complex photodecomposition pathways operative in condensed phases

Two’s Company, Three’s a Crowd: Exciton Localization in Cofacially Arrayed Polyfluorenes

Understanding the mechanisms of long-range energy transfer through polychromophoric assemblies is critically important in photovoltaics and biochemical systems. Using a set of cofacially arrayed polyfluorenes (F<i>n</i>), we investigate the mechanism of (singlet) exciton delocalization in π-stacked polychromophoric assemblies. Calculations reveal that effective stabilization of an excimeric state requires an ideal sandwich-like arrangement; yet surprisingly, emission spectroscopy indicates that exciton delocalization is limited to only two fluorene units for all <i>n</i>. Herein, we show that delocalization is determined by the interplay between the energetic gain from delocalization, which quickly saturates beyond two units in larger F<i>n</i>, and an energetic penalty associated with structural reorganization, which increases linearly with <i>n</i>. With these insights, we propose a hopping mechanism for exciton transfer, based upon the presence of multiple excimeric tautomers of similar energy in larger polyfluorenes (<i>n</i> ≥ 4) together with the anticipated low thermal barrier of their interconversion

Photoinduced Electron Transfer in Donor–Acceptor Complexes of Ethylene with Molecular and Atomic Iodine

Building upon our recent studies of radical addition pathways following excitation of the I₂ chromophore in the donor–acceptor complex of ethylene and I₂ (C₂H₄···I₂), in this article, we extend our studies to examine photoinduced electron transfer. Thus, irradiation into the intense charge-transfer band of the complex (λ_max = 247 nm) gave rise to a band at 366 nm that is assigned to the bridged ethylene–I radical complex on the basis of our prior work. The formation of the radical complex is explained by a mechanism that involves rapid back electron transfer leading to I–I bond fission. Excitation into the charge-transfer band of the radical complex led to regeneration of the parent complex and the formation of the final photoproduct, <i>anti</i>- and <i>gauche</i>-1,2-diiodoethane, which confirms that the reaction proceeds ultimately by a radical addition mechanism. This finding is contrasted with our previous study of the C₂H₄···Br₂ complex, where CT excitation led to only one product, <i>anti</i>-1,2-dibromoethane, a result explained by a single electron-transfer mechanism proceeding via a bridged bromonium ion intermediate. For the I₂ complex, the breakup of the photolytically generated I₂^–• anion radical is apparently sufficiently slow to render it uncompetitive with back electron transfer. Finally, we report a detailed computational examination of the parent and radical complexes of both bromine and iodine, using high-level single- and multireference methods, which provide insight into the different behaviors of the charge-transfer states of the two radicals and the role of spin–orbit coupling

Excitonic Coupling in Fluorene-Based Bichromophoric Systems: Vibrational Quenching and the Transition from Weak to Intermediate Coupling

Excimeric systems (i.e., excited dimers) have well served as model compounds for the study of the delocalization of electronic energy over weakly interacting chromophores. However, there remain relatively few isolated systems in which such interactions can be studied experimentally at a level to afford detailed comparisons with theory. In this Article, we examine a series of covalently and noncovalently linked dimers of fluorene, as a model aromatic chromophore, where the formation of excimers requires a π-stacked, cofacial orientation at van der Waals contact. Building upon a series of seminal prior studies that examined vibronic quenching of the excitation interaction in van der Waals dimers, the key question that we sought to address here is whether a single quenching factor could reproduce experimental excitonic splittings across a series of covalently and noncovalently linked bichromophoric systems built from the same chromophore. In comparing experimentally measured excitonic splittings with calculated static splittings using time-dependent density functional methods, we find that all systems save one fall on a line with a slope of 0.080(8), reflecting a vibrational quenching of roughly 1 order of magnitude. The outlier, which shows a significantly reduced quenching factor, represents a cyclophane-linked system where the fluorene moieties are constrained in a cofacial arrangement. We argue that this system evidences the transition from the weak to intermediate coupling regime

Photochemistry of Furyl- and Thienyldiazomethanes: Spectroscopic Characterization of Triplet 3-Thienylcarbene

Photolysis (λ > 543 nm) of 3-thienyldiazomethane (<b>1</b>), matrix isolated in Ar or N₂ at 10 K, yields triplet 3-thienylcarbene (<b>13</b>) and α-thial-methylenecyclopropene (<b>9</b>). Carbene <b>13</b> was characterized by IR, UV/vis, and EPR spectroscopy. The conformational isomers of 3-thienylcarbene (<i>s</i>-<i>E</i> and <i>s</i>-<i>Z</i>) exhibit an unusually large difference in zero-field splitting parameters in the triplet EPR spectrum (|<i>D</i>/<i>hc</i>| = 0.508 cm^–1, |<i>E</i>/<i>hc</i>| = 0.0554 cm^–1; |<i>D</i>/<i>hc</i>| = 0.579 cm^–1, |<i>E</i>/<i>hc</i>| = 0.0315 cm^–1). Natural Bond Orbital (NBO) calculations reveal substantially differing spin densities in the 3-thienyl ring at the positions adjacent to the carbene center, which is one factor contributing to the large difference in <i>D</i> values. NBO calculations also reveal a stabilizing interaction between the sp orbital of the carbene carbon in the <i>s</i>-<i>Z</i> rotamer of <b>13</b> and the antibonding σ orbital between sulfur and the neighboring carbonan interaction that is not observed in the <i>s</i>-<i>E</i> rotamer of <b>13</b>. In contrast to the EPR spectra, the electronic absorption spectra of the rotamers of triplet 3-thienylcarbene (<b>13</b>) are indistinguishable under our experimental conditions. The carbene exhibits a weak electronic absorption in the visible spectrum (λ_max = 467 nm) that is characteristic of triplet arylcarbenes. Although studies of 2-thienyldiazomethane (<b>2</b>), 3-furyldiazomethane (<b>3</b>), or 2-furyldiazomethane (<b>4</b>) provided further insight into the photochemical interconversions among C₅H₄S or C₅H₄O isomers, these studies did not lead to the spectroscopic detection of the corresponding triplet carbenes (2-thienylcarbene (<b>11</b>), 3-furylcarbene (<b>23</b>), or 2-furylcarbene (<b>22</b>), respectively)

Reactive Pathways in the Chlorobenzene–Ammonia Dimer Cation Radical: New Insights from Experiment and Theory

Building upon our recent studies of noncovalent interactions in chlorobenzene and bromobenzene clusters, in this work we focus on interactions of chlorobenzene (PhCl) with a prototypical N atom donor, ammonia (NH₃). Thus, we have obtained electronic spectra of PhCl···(NH₃)_<i>n</i> (<i>n</i> = 1–3) complexes in the region of the PhCl monomer S₀ −S₁ (ππ*) transition using resonant 2-photon ionization (R2PI) methods combined with time-of-flight mass analysis. Consistent with previous studies, we find that upon ionization the PhCl···NH₃ dimer cation radical reacts primarily via Cl atom loss. A second channel, HCl loss, is identified for the first time in R2PI studies of the 1:1 complex, and a third channel, H atom loss, is identified for the first time. While prior studies have assumed the dominance of a π-type complex, we find that the reactive complex corresponds instead to an in-plane σ-type complex. This is supported by electronic structure calculations using density functional theory and post-Hartree–Fock methods and Franck–Condon analysis. The reactive pathways in this system were extensively characterized computationally, and consistent with results from previous calculations, we find two nearly isoenergetic arenium ions (Wheland intermediates; denoted WH1, WH2), which lie energetically below the initially formed dimer cation radical complex. At the energy of our experiment, intermediate WH1, produced from <i>ipso</i>-addition, is not stable with respect to Cl or HCl loss, and the relative branching between these channels observed in our experiment is well reproduced by microcanonical transition state theory calculations based upon the calculated parameters. Intermediate WH2, where NH₃ adds ortho to the halogen, decomposes over a large barrier via H atom loss to form protonated <i>o</i>-chloroaniline. This channel is not open at the (2-photon) energy of our experiments, and it is suggested that photodissociation of a long-lived (i.e., several ns) WH2 intermediate leads to the observed products

Excitation Spectra of the Jet-Cooled 4‑Phenylbenzyl and 4‑(4′-Methylphenyl)benzyl Radicals

The excitation spectra of jet-cooled 4-phenylbenzyl and 4-(4′-methylphenyl)­benzyl radicals have been identified by a combination of resonant two-color two-photon ionization mass spectrometry and quantum chemical methods. Both radicals exhibit progressions in the biphenyl torsional mode, peaking near ν = 17. The lowest observed peak for 4-phenylbenzyl was observed at 18598 cm^–1 and is estimated to be the ν = 3 of the progression, while the lowest observed peak for the 4-(4′-methylphenyl)­benzyl radical was observed at 18183 cm^–1 and is possibly the origin. The spectra are discussed and compared to other biphenyl and benzyl chromophores