| 1. |
- Allum, Felix, et al.
(författare)
-
Coulomb explosion imaging of CH3I and CH2CII photodissociation dynamics
- 2018
-
Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 149:20
-
Tidskriftsartikel (refereegranskat)abstract
- The photodissociation dynamics of CH3I and CH2CII at 272 nm were investigated by time-resolved Coulomb explosion imaging, with an intense non-resonant 815nmprobe pulse. Fragment ion momenta over a widem/z range were recorded simultaneously by coupling a velocity map imaging spectrometer with a pixel imaging mass spectrometry camera. For both molecules, delay-dependent pump-probe features were assigned to ultraviolet-induced carbon-iodine bond cleavage followed by Coulomb explosion. Multi-mass imaging also allowed the sequential cleavage of both carbon-halogen bonds in CH2ClI to be investigated. Furthermore, delay-dependent relative fragment momenta of a pair of ions were directly determined using recoil-frame covariance analysis. These results are complementary to conventional velocity map imaging experiments and demonstrate the application of time-resolved Coulomb explosion imaging to photoinduced real-time molecular motion.
|
|
| 2. |
- Brasse, Felix, et al.
(författare)
-
Time-resolved inner-shell photoelectron spectroscopy : From a bound molecule to an isolated atom
- 2018
-
Ingår i: Physical Review A: covering atomic, molecular, and optical physics and quantum information. - 2469-9926 .- 2469-9934. ; 97:4
-
Tidskriftsartikel (refereegranskat)abstract
- Due to its element and site specificity, inner-shell photoelectron spectroscopy is a widely used technique to probe the chemical structure of matter. Here, we show that time-resolved inner-shell photoelectron spectroscopy can be employed to observe ultrafast chemical reactions and the electronic response to the nuclear motion with high sensitivity. The ultraviolet dissociation of iodomethane (CH3I) is investigated by ionization above the iodine 4d edge, using time-resolved inner-shell photoelectron and photoion spectroscopy. The dynamics observed in the photoelectron spectra appear earlier and are faster than those seen in the iodine fragments. The experimental results are interpreted using crystal-field and spin-orbit configuration interaction calculations, and demonstrate that time-resolved inner-shell photoelectron spectroscopy is a powerful tool to directly track ultrafast structural and electronic transformations in gas-phase molecules.
|
|
| 3. |
- Burt, Michael, et al.
(författare)
-
Coulomb-explosion imaging of concurrent CH2BrI photodissociation dynamics
- 2017
-
Ingår i: Physical Review A: covering atomic, molecular, and optical physics and quantum information. - 2469-9926 .- 2469-9934. ; 96:4
-
Tidskriftsartikel (refereegranskat)abstract
- The dynamics following laser-induced molecular photodissociation of gas-phase CH2BrI at 271.6 nm were investigated by time-resolved Coulomb-explosion imaging using intense near-IR femtosecond laser pulses. The observed delay-dependent photofragment momenta reveal that CH2BrI undergoes C-I cleavage, depositing 65.6% of the available energy into internal product states, and that absorption of a second UV photon breaks the C-Br bond of C(H)2Br. Simulations confirm that this mechanism is consistent with previous data recorded at 248 nm, demonstrating the sensitivity of Coulomb-explosion imaging as a real-time probe of chemical dynamics.
|
|
| 4. |
- Hambäck, Peter A., et al.
(författare)
-
Effects of plant neighborhoods on plant-herbivore interactions : resource dilution and associational effects
- 2014
-
Ingår i: Ecology. - : Wiley. - 0012-9658 .- 1939-9170. ; 95:5, s. 1370-1383
-
Tidskriftsartikel (refereegranskat)abstract
- Effects of neighboring plants on herbivore damage to a focal plant (associational effects) have been documented in many systems and can lead to either increased or decreased herbivore attack. Mechanistic models that explain the observed variety of herbivore responses to local plant community composition have, however, been lacking. We present a model of herbivore responses to patches that consist of two plant types, where herbivore densities on a focal plant are determined by a combination of patch-finding, within-patch redistribution, and patch-leaving. Our analyses show that the effect of plant neighborhood on herbivores depends both on how plant and herbivore traits combine to affect herbivore movement and on how experimental designs reveal the effects of plant density and plant relative frequency. Associational susceptibility should be the dominant pattern when herbivores have biased landing rates within patches. Other behavioral decision rules lead to mixed responses, but a common pattern is that in mixed patches, one plant type experiences associational resistance while the other plant experiences associational susceptibility. In some cases, the associational effect may shift sign along a gradient of plant frequency, suggesting that future empirical studies should include more than two plant frequencies to detect nonlinearities. Finally, we find that associational susceptibility should be commonly observed in experiments using replacement designs, whereas associational resistance will be the dominant pattern when using additive designs. Consequently, outcomes from one experimental design cannot be directly compared to studies with other designs. Our model can also be translated to other systems with foragers searching for multiple resource types.
|
|
| 5. |
- Inouye, Brian D., et al.
(författare)
-
Phenology as a process rather than an event : from individual reaction norms to community metrics
- 2019
-
Ingår i: Ecological Monographs. - : Wiley. - 0012-9615 .- 1557-7015. ; 89:2
-
Tidskriftsartikel (refereegranskat)abstract
- Measures of the seasonal timing of biological events are key to addressing questions about how phenology evolves, modifies species interactions, and mediates biological responses to climate change. Phenology is often characterized in terms of discrete events, such as a date of first flowering or arrival of first migrants. We discuss how phenological events that are typically measured at the population or species level arise from distributions of phenological events across seasons, and from norms of reaction of these phenological events across environments. We argue that individual variation in phenological distributions and reaction norms has important implications for how we should collect, analyze, and interpret phenological information. Regarding phenology as a reaction norm rather than one year's specific values implies that selection acts on the phenologies that an individual expresses over its lifetime. To understand how climate change is likely to influence phenology, we need to consider not only plastic responses along the reaction norm but changes in the reaction norm itself. We show that when individuals vary in their reaction norms, correlations between reaction norm elevation and slope make first events particularly poor estimators of population sensitivity to climate change, and variation in slopes can obscure the pattern of selection on phenology. We also show that knowing the shape of the distribution of phenological events across the season is important for predicting biologically important phenological mismatches with climate change. Last, because phenological events are parts of a continuous developmental process, we suggest that the approach of measuring phenology by recording developmental stages of individuals in a population at a single point in time should be used more widely. We conclude that failure to account for phenological distributions and reaction norms may lead to overinterpretation of metrics based on single events, such as commonly recorded first event dates, and may confound meta-analyses that use a range of metrics. Rather than prescribing a single universal approach to studying phenology, we point out limitations of inferences based on single metrics and encourage work that considers the multivariate nature of phenology and more tightly links data collection and analyses with biological hypotheses.
|
|
| 6. |
- Underwood, Nora, et al.
(författare)
-
A CONCEPTUAL FRAMEWORK FOR ASSOCIATIONAL EFFECTS : WHEN DO NEIGHBORS MATTER AND HOW WOULD WE KNOW?
- 2014
-
Ingår i: The Quarterly review of biology. - : UNIV CHICAGO PRESS. - 0033-5770 .- 1539-7718. ; 89:1, s. 1-19
-
Forskningsöversikt (refereegranskat)abstract
- Interactions between individual consumer and resource organisms can be modified by neighbors, e.g., when herbivory depends on the identity or diversity of neighboring plants. Effects of neighbors on consumer-resource interactions (associational effects) occur in many systems, including plant-herbivore interactions, predator-prey interactions (mimicry), and plant-pollinator interactions. Unfortunately, we know little about how ecologically or evolutionarily important these effects are because we lack appropriate models and data to determine how neighbor effects on individuals contribute to net interactions at population and community levels. Here we supply a general definition of associational effects, review relevant theory, and suggest strategies for future theoretical and empirical work. We find that mathematical models from a variety of fields suggest that individual-level associational effects will influence population and community dynamics when associational effects create local frequency dependence. However, there is little data on how local frequency dependence in associational effects is generated, or on the form or spatial scale of that frequency dependence. Similarly, existing theory lacks consideration of nonlinear and spatially explicit frequency dependence. We outline an experimental approach for producing data that can be related to models to advance our understanding of how associational effects contribute to population and community processes.
|
|
| 7. |
- Underwood, Nora, et al.
(författare)
-
Pollinators, Herbivores, and Plant Neighborhood Effects
- 2020
-
Ingår i: The Quarterly review of biology. - : University of Chicago Press. - 0033-5770 .- 1539-7718. ; 95:1, s. 37-57
-
Forskningsöversikt (refereegranskat)abstract
- Pollinator and herbivore interactions with individual plants can be strongly influenced by the densities and frequencies of other plants in local neighborhoods. The importance of these neighborhood effects is not yet clear, due in part to a profound disconnect between studies of pollinator and herbivore neighborhood effects. Considering these effects jointly is critical for understanding the role of plant spatial heterogeneity because plant fitness is often affected by pollinators, herbivores, and their interactions. We bring together these two types of neighborhood effects, describing the pathways through which these insects mediate neighborhood effects, and comparing their implementation in mathematical models. We find that ideas from each field can improve work in the other. For example, pollinator theory should broaden consideration of how pollinator traits influence responses to plant neighborhoods, while herbivore theory should consider adaptive foraging and connect herbivore neighborhood effects to plant fitness. We discuss approaches to theory that integrate pollinator and herbivore effects, particularly considering the nested spatial and temporal scales of these insects' responses to neighborhoods. Ultimately, models will need to combine neighborhood effects from the diverse species that affect plants with direct plant interactions to determine the importance of spatial structure for plant performance and evolution.
|
|
| 8. |
- Glasbey, JC, et al.
(författare)
-
- 2021
-
swepub:Mat__t
|
|
