Circular dichroism in photoelectron angular distributions from two‐color (1+1) REMPI of NO

A detailed experimental and theoretical study of dichroic effects in photoelectron angular distributions is reported for (1+1), two‐color REMPI of NO via the A^ 2Σ^+, v=0 state. Optically aligned A state rotational levels are probed through ionization by circularly polarized light. Resultant photoelectron angular distributions exhibit significant left–right asymmetry, the phase and magnitude of which are shown to be related to the curvature of the excited state M_J distribution. Theoretical calculations involving a full ab initio treatment of the ionization dynamics result in circularly dichroic angular distribution (CDAD) parameters in good agreement with those derived experimentally. Additional effects including hyperfine depolarization and coherence are also discussed in relation to the observed CDAD data

A multiphoton ionization study of the photodissociation dynamics of the S_2 state of CH_3ONO

Two‐color (1+1) REMPI (resonantly enhanced multiphoton ionization) photoelectron spectroscopy is used to probe the NO photofragments produced by the UV photodissociation of methyl nitrite, i.e., CH_3ONO+hν→CH_3ONO∗(S_2)→CH_3O⋅(X)+NO(X, v, J). The photofragments are produced in their ground electronic states but with high rotational and translational energy. NO fragment angular distributions, rotational state distributions, and spatial alignment are determined by photoion and photoelectron detection. The initial state alignment is obtained by the CDAD (circularly dichroic angular distribution) technique for the first time. CDAD measurements for rotational levels with 35.5≤J≤46.5 result in alignment parameters at the classical high‐J limit of A^(2)_0 =−0.4. This alignment is consistent with an ‘‘impulsive’’ dissociation mechanism in which photofragment recoil along the CH_3O–NO bond imparts substantial rotational angular momentum to the NO molecule resulting in a high‐J state distribution and preferential rotation in the plane of dissociation. These measurements clearly establish the utility of the CDAD method for probing chemical processes in which spatial alignment plays an important role. Photoion angular distributions are used to probe correlations between the CH_3ONO transition dipole moment, NO fragment velocity, and angular momentum. These correlations reveal additional details of the photolysis mechanism

Light and flow regimes regulate the metabolism of rivers

Mean annual temperature and mean annual precipitation drive much of the variation in productivity across Earth's terrestrial ecosystems but do not explain variation in gross primary productivity (GPP) or ecosystem respiration (ER) in flowing waters. We document substantial variation in the magnitude and seasonality of GPP and ER across 222 US rivers. In contrast to their terrestrial counterparts, most river ecosystems respire far more carbon than they fix and have less pronounced and consistent seasonality in their metabolic rates. We find that variation in annual solar energy inputs and stability of flows are the primary drivers of GPP and ER across rivers. A classification schema based on these drivers advances river science and informs management.We thank Ted Stets, Jordan Read, Tom Battin, Sophia Bonjour, Marina Palta, and members of the Duke River Center for their help in developing these ideas. This work was supported by grants from the NSF 1442439 (to E.S.B. and J.W.H.), 1834679 (to R.O.H.), 1442451 (to R.O.H.), 2019528 (to R.O.H. and J.R.B.), 1442140 (to M.C.), 1442451 (to A.M.H.), 1442467 (to E.H.S.), 1442522 (to N.B.G.), 1624807 (to N.B.G.), and US Geological Survey funding for the working group was supported by the John Wesley Power Center for Analysis and Synthesis. Phil Savoy contributed as a postdoc- toral associate at Duke University and as a postdoctoral associate (contractor) at the US Geological Survey

The role of epigenetics in renal ageing

An ability to separate natural ageing processes from processes specific to morbidities is required to understand the heterogeneity of age-related organ dysfunction. Mechanistic insight into how epigenetic factors regulate ageing throughout the life course, linked to a decline in renal function with ageing, is already proving to be of value in the analyses of clinical and epidemiological cohorts. Noncoding RNAs provide epigenetic regulatory circuits within the kidney, which reciprocally interact with DNA methylation processes, histone modification and chromatin. These interactions have been demonstrated to reflect the biological age and function of renal allografts. Epigenetic factors control gene expression and activity in response to environmental perturbations. They also have roles in highly conserved signalling pathways that modulate ageing, including the mTOR and insulin/insulin-like growth factor signalling pathways, and regulation of sirtuin activity. Nutrition, the gut microbiota, inflammation and environmental factors, including psychosocial and lifestyle stresses, provide potential mechanistic links between the epigenetic landscape of ageing and renal dysfunction. Approaches to modify the renal epigenome via nutritional intervention, targeting the methylome or targeting chromatin seem eminently feasible, although caution is merited owing to the potential for intergenerational and transgenerational effects

AN EXAMINATION OF THE RESONANT MULTIPHOTON IONIZATION OF CF3ICF_{3}I

Author Institution: Department of Chemistry, University of Cincinnati; Department of Chemistry, University of KentuckyResonant $(2+1)$ multiphoton ionization (MPI) has been observed in the 300--306 nm excitation region for both cold molecular beam and room temperature samples of $CF_{3}I$. Excitation spectra with mass-selected ion detection will be presented and discussed. MPI/photoelectron spectra of $CF_{3}I$ will be used to demonstrate that parent $CF_{3}I^{+}$ ions are produced predominantely in their ground $\tilde{X} ^{2}E_{1/2}$ state. Tentative spectral assignments based on the photoion and photoelectron data have been made

Structures, Energetics and Fragmentation Pathways of C\u3cem\u3e\u3csub\u3en\u3c/sub\u3e\u3c/em\u3eH\u3csub\u3e2\u3c/sub\u3e\u3csup\u3e2+\u3c/sup\u3e Carbodications

Potential energy curves have been calculated for CnH22+ (n = 2−9) ions and results have been compared with data on unimolecular charge-separation reactions obtained by Rabrenovi{\\u27{c}} and Beynon. Geometry-optimized, minimum energy, linear CnH22+ structures have been computed for ground and low-lying excited states. These carbodications exist in stable configurations with well depths greater than 3 eV. Decomposition pathways into singly charged fragment ions lead to products with computed kinetic energies in excess of 1 eV. A high degree of correlation exists between experimental information and results computed for linear CnH22+ structures having hydrogen atoms on each end. The exception involves C4H22+ reactions where a low-lying doubly charged isomer must be invoked to rationalize the experimental data