Conical intersections play a critical role in excited-state dynamics of polyatomic molecules because they govern the reaction pathways of many nonadiabatic processes. However, ultrafast probes have lacked sufficient spatial resolution to image wave-packet trajectories through these intersections directly. Here, we present the simultaneous experimental characterization of one-photon and two-photon excitation channels in isolated CFI molecules using ultrafast gas-phase electron diffraction. In the two-photon channel, we have mapped out the real-space trajectories of a coherent nuclear wave packet, which bifurcates onto two potential energy surfaces when passing through a conical intersection. In the one-photon channel, we have resolved excitation of both the umbrella and the breathing vibrational modes in the CF fragment in multiple nuclear dimensions. These findings benchmark and validate ab initio nonadiabatic dynamics calculations.

The ultrafast photoinduced ring-opening of 1,3-cyclohexadiene constitutes a textbook example of electrocyclic reactions in organic chemistry and a model for photobiological reactions in vitamin D synthesis. Here, we present direct and unambiguous observation of the ring-opening reaction path on

Simultaneous observation of nuclear and electronic motion is crucial for a complete understanding of molecular dynamics in excited electronic states. It is challenging for a single experiment to independently follow both electronic and nuclear dynamics at the same time. Here we show that ultrafast electron diffraction can be used to simultaneously record both electronic and nuclear dynamics in isolated pyridine molecules, naturally disentangling the two components. Electronic state changes (S1→S0 internal conversion) were reflected by a strong transient signal in small-angle inelastic scattering, and nuclear structural changes (ring puckering) were monitored by large-angle elastic diffraction. Supported by ab initio nonadiabatic molecular dynamics and diffraction simulations, our experiment provides a clear view of the interplay between electronic and nuclear dynamics of the photoexcited pyridine molecule.

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The 2015 to 2017 outbreak of Zika generated global attention on the risk of a spectrum of neurological disorders posed to women and their unborn children-including, but not limited to, microcephaly-that came to be known as congenital Zika syndrome (CZS). Images of women cradling babies born with CZS underscored the gendered nature of the epidemic. Nonetheless, the media attention towards the highly gendered dimensions of the outbreak was not matched by a recognition of the importance of female participation in the decision-making for the control of the Aedes aegypti mosquito, the vector responsible for the spread of Zika. Moreover, while women were the target population of the public health response to the epidemic, the impact of arbovirus policies on women was largely neglected. This paradox-the absence of gender in the policy response to a problem where the gender dimensions were evident from the start-adds to other questions about the sustainability of arbovirus control. The Zika epidemic is but one element of a broader problem with arboviruses-including dengue fever, yellow fever, and chikungunya-which by and large remain neglected across Latin America (and much of the world). Dengue fever, spread by the same A. aegypti mosquito, has shown considerable growth across the continent in recent years [1]. For example, Brazil reported close to 1.5 million cases of the disease between 2014 and 2016 [2]. This is mirrored across Latin America, where there have been almost 700,000 reported cases so far in 2019 alone [3]. Similarly, the region is witnessing the highest rates of other diseases transmitted by A. aegypti. This includes yellow fever-particularly in Brazil [4] [5]-and chikungunya, which was only introduced to the hemisphere in 2013 and is now present in almost every country in the region, causing a significant morbidity burden [6]. Another question pertains to the complex history of arbovirus control in the region, which has demonstrated some notable, if only temporary, successes [7]. Recognition of this history and of the historical ecology of mosquitoes in the region is essential for the effectiveness of present programs, which thus far have repeated the mistakes of the past. Brazil has eliminated A aegypti numerous times [8] [9]. Nonetheless, the preference for vertical programs focusing on the "war" against Aedes has led to short-lived results, with mosquitoes returning within years, due, in a large part, to the absence of a coordinated regional response and the failure to consider and integrate the socioeconomic and structural determinants that enable mosquitoes to thrive. These include substandard living conditions, including those that result from rapid urbanization, increasing population density, poor quality housing, and inadequate sanitary and health facilities, along with lasting public sector deficiencies such as lack of routine water

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The conversion of light into usable chemical and mechanical energy is pivotal to several biological and chemical processes, many of which occur in solution. To understand the structure–function relationships mediating these processes, a technique with high spatial and temporal resolutions is required. Here, we report on the design and commissioning of a liquid-phase mega-electron-volt (MeV) ultrafast electron diffraction instrument for the study of structural dynamics in solution. Limitations posed by the shallow penetration depth of electrons and the resulting information loss due to multiple scattering and the technical challenge of delivering liquids to vacuum were overcome through the use of MeV electrons and a gas-accelerated thin liquid sheet jet. To demonstrate the capabilities of this instrument, the structure of water and its network were resolved up to the 3rd hydration shell with a spatial resolution of 0.6 Å; preliminary time-resolved experiments demonstrated a temporal resolution of 200 fs.

Capturing OH(H 3 O + ) in ionized water Recent advances in liquid-phase ultrafast electron diffraction techniques make it possible to observe what has only been theoretically presumed to occur at short times upon interaction of ionizing radiation with liquid water. Lin et al . provide direct evidence for capturing the short-lived radical-cation pair OH(H 3 O + ), which has been hypothesized for years to form after ionization of liquid water but was not structurally resolved previously (see the Perspective by Cao et al .). The authors trace dissociation and subsequent nonradiative structural relaxation around the ionization center. —YS