The hydrogen-bonded and free OH stretch modes of Cl -(H 2 O) n (n ) 1-5) have been observed by vibrational predissociation spectroscopy in the 2.6-3.2 µm region. Besides demonstrating that all clusters form strong ionic hydrogen bonds, the spectra provide clear evidence of water-water hydrogen-bonding networks in n ) 4 and n ) 5, with the broad spectrum of n ) 5 resembling that of large neutral water clusters. No waterwater hydrogen bonding is seen in n ) 2 and n ) 3, but these clusters appear to be solvated asymmetrically. While the data suggest that Clion is solvated on the surface of water clusters, there are discrepancies between the observed spectra and ab initio predictions. This disagreement may stem from either zero-point motion or high cluster temperature, which tend to disrupt hydrogen bonding among the waters.

Incipient sympatric speciation in blind mole rat, Spalax galili, in Israel, caused by sharp ecological divergence of abutting chalkbasalt ecologies, has been proposed previously based on mitochondrial and whole-genome nuclear DNA. Here, we present new evidence, including transcriptome, DNA editing, microRNA, and codon usage, substantiating earlier evidence for adaptive divergence in the abutting chalk and basalt populations. Genetic divergence, based on the previous and new evidence, is ongoing despite restricted gene flow between the two populations. The principal component analysis, neighbor-joining tree, and genetic structure analysis of the transcriptome clearly show the clustered divergent two mole rat populations. Gene-expression level analysis indicates that the population transcriptome divergence is displayed not only by soil divergence but also by sex. Gene ontology enrichment of the differentially expressed genes from the two abutting soil populations highlights reproductive isolation. Alternative splicing variation of the two abutting soil populations displays two distinct splicing patterns. L-shaped F ST distribution indicates that the two populations have undergone divergence with gene flow. Transcriptome divergent genes highlight neurogenetics and nutrition characterizing the chalk population, and energetics, metabolism, musculature, and sensory perception characterizing the abutting basalt population. Remarkably, microRNAs also display divergence between the two populations. The GC content is significantly higher in chalk than in basalt, and stress-response genes mostly prefer nonoptimal codons. The multiple lines of evidence of ecologicalgenomic and genetic divergence highlight that natural selection overrules the gene flow between the two abutting populations, substantiating the sharp ecological chalk-basalt divergence driving sympatric speciation.natural selection | ecological adaptive speciation | DNA editing | microRNA regulation | nonoptimal codon usage

Predissociation spectra in the 2.6−3.3 μm region were observed for protonated chlorine nitrate and protonated nitric acid as well as some of their isotopomers (HXNO3 +, X = H, D, 35Cl, 37Cl). Two protonated isomers of both ClONO2 and HNO3 were identified from the vibrational spectra. The lowest energy isomer was the ion−molecule complex NO2 +(HOX) formed by protonation of the XO group. The second isomer was the metastable species (HO)(XO)NO+ formed by protonation of a terminal oxygen; this isomer was generated only under hotter ionizing conditions. The vibrational band centers of these isomers agreed well with ab initio predictions. Vibrational excitation of the HXNO3 + species studied here led solely to NO2 + + HOX products. Predissociation of the covalently bound metastable isomers (HO)(XO)NO+ to these products required an IR-induced rearrangement involving simultaneous 1,3 hydrogen shift and charge transfer. The results presented here were consistent with predictions of ab initio calculations and previous mass spectrometric and kinetic studies.

Clusters composed of solvated ions provide a valuable prototype system for studying molecular aspects of solvation. Vibrational spectroscopy can provide insight into how the solvent structure around an ion evolves with cluster size. We describe studies which illustrate the effects of adding small numbers of solvent molecules to anions. Halide ions are among the most ubiquitous and fundamental anions in aqueous chemistry. Recent calculations and photoelectron spectroscopy experiments suggest that hydrated halide ion clusters X(H2O) have structures in which the anion binds to the surface of water clusters, rather than being surrounded by solvent water molecules (socalIed interior states). We have observed infrared spectra for a series of solvated chloride ions which can be assigned with the aid of ab initio calculations. We find that for the chloride ion the water molecules tend to associate, but that waterwater hydrogen bonds are not necessarily formed at the smallest size. Our results suggest the importance of entropic factors in these floppy clusters. Evidence is also found for a possible transition to liquid-like structures at a critical cluster size.