Fluorescence and ZEKE spectroscopy of small, jet-cooled aromatic molecules

A detailed spectroscopic analysis is presented for the S1 ↔ S0 and D0 + ← S1 transitions of meta-fluorotoluene (mFT) and N-methylpyrrole (NMP) through resonance-enhanced multiphoton ionisation (REMPI), laser-induced fluorescence (LIF), dispersed fluorescence (DF), two-dimensional laser-induced fluorescence (2DLIF) and zero-electron-kinetic-energy (ZEKE) spectroscopy. Assignments have been made for various vibrations, torsions and vibration-torsion bands in these spectra, detailing the energy levels in the three electronic states. These studies comprise the most comprehensive spectroscopic studies of these two molecules to date. For mFT, discussion has been made regarding how vibration-vibration and vibrationtorsion eigenstates couple together and how this evolves from a purely localised, restricted coupling mechanism at low internal energies to widespread, dissipative intramolecular vibrational energy redistribution (IVR) at only modest internal energy. Furthermore, an extreme case of Duschinsky mixing has been examined, which manifests itself in the spectra in a similar way to anharmonic coupling; this has been elucidated through a combination of emission and excitation spectroscopy, quantum chemical calculations and a comparison to meta-chlorotoluene (mClT), in which this mixing is also present, yet not so extreme. In the D0 + cationic state, the activity observed is discussed largely in terms of significant changes in torsional potential compared to the S1 state, leading to off-diagonal torsional transitions having considerable, and often dominant, intensities. Additionally, the ZEKE spectra appear less enlightening in ascertaining the assignment of the activity in S1 than do the 2DLIF spectra, although they are useful as a confirmatory/diagnostic tool. The S1 ← S0 transition of NMP is electric dipole forbidden and, as such, the activity observed in the REMPI and LIF spectra is largely due to vibronic coupling with nearby, higher-lying electronic states. Routes for the observed vibronic coupling have been proposed and discussed, alongside commentary regarding the results of previous photodynamical studies. The ZEKE spectra of NMP have been investigated, which exhibit highly diagonal Franck-Condon factors, except for those via the b1 symmetry, ring-localised modes. Nevertheless, it was possible to derive a precise adiabatic ionisation energy (AIE) of 64250 ± 5 cm-1. The 2D-LIF spectra are significantly more complicated than one might expect. Furthermore, a new labelling scheme for N-substituted pyrroles is proposed, which allows for the comparison of vibrations of different molecules of the same symmetry class, which are expected to be valid for almost all (reasonable) substituents. This scheme is similar to those proposed for mono- and disubstituted benzene molecules, and the corresponding scheme for meta-disubstituted benzenes is used in the analysis of mFT. Finally, REMPI and ZEKE spectra have been recorded for the first time, of the NMP-RG (RG = Ar, Kr) complexes, noting that the presence of the rare gas is sufficient to perturb the electronic structure to allow the observance of the NMP-RG origin in the REMPI spectra. Furthermore, we deduce AIEs of 64077 ± 5 cm-1 and 64029 ± 5 cm-1 for NMP-Ar and NMP-Kr, respectively

Fluorescence and ZEKE spectroscopy of small, jet-cooled aromatic molecules

A detailed spectroscopic analysis is presented for the S1 ↔ S0 and D0 + ← S1 transitions of meta-fluorotoluene (mFT) and N-methylpyrrole (NMP) through resonance-enhanced multiphoton ionisation (REMPI), laser-induced fluorescence (LIF), dispersed fluorescence (DF), two-dimensional laser-induced fluorescence (2DLIF) and zero-electron-kinetic-energy (ZEKE) spectroscopy. Assignments have been made for various vibrations, torsions and vibration-torsion bands in these spectra, detailing the energy levels in the three electronic states. These studies comprise the most comprehensive spectroscopic studies of these two molecules to date. For mFT, discussion has been made regarding how vibration-vibration and vibrationtorsion eigenstates couple together and how this evolves from a purely localised, restricted coupling mechanism at low internal energies to widespread, dissipative intramolecular vibrational energy redistribution (IVR) at only modest internal energy. Furthermore, an extreme case of Duschinsky mixing has been examined, which manifests itself in the spectra in a similar way to anharmonic coupling; this has been elucidated through a combination of emission and excitation spectroscopy, quantum chemical calculations and a comparison to meta-chlorotoluene (mClT), in which this mixing is also present, yet not so extreme. In the D0 + cationic state, the activity observed is discussed largely in terms of significant changes in torsional potential compared to the S1 state, leading to off-diagonal torsional transitions having considerable, and often dominant, intensities. Additionally, the ZEKE spectra appear less enlightening in ascertaining the assignment of the activity in S1 than do the 2DLIF spectra, although they are useful as a confirmatory/diagnostic tool. The S1 ← S0 transition of NMP is electric dipole forbidden and, as such, the activity observed in the REMPI and LIF spectra is largely due to vibronic coupling with nearby, higher-lying electronic states. Routes for the observed vibronic coupling have been proposed and discussed, alongside commentary regarding the results of previous photodynamical studies. The ZEKE spectra of NMP have been investigated, which exhibit highly diagonal Franck-Condon factors, except for those via the b1 symmetry, ring-localised modes. Nevertheless, it was possible to derive a precise adiabatic ionisation energy (AIE) of 64250 ± 5 cm-1. The 2D-LIF spectra are significantly more complicated than one might expect. Furthermore, a new labelling scheme for N-substituted pyrroles is proposed, which allows for the comparison of vibrations of different molecules of the same symmetry class, which are expected to be valid for almost all (reasonable) substituents. This scheme is similar to those proposed for mono- and disubstituted benzene molecules, and the corresponding scheme for meta-disubstituted benzenes is used in the analysis of mFT. Finally, REMPI and ZEKE spectra have been recorded for the first time, of the NMP-RG (RG = Ar, Kr) complexes, noting that the presence of the rare gas is sufficient to perturb the electronic structure to allow the observance of the NMP-RG origin in the REMPI spectra. Furthermore, we deduce AIEs of 64077 ± 5 cm-1 and 64029 ± 5 cm-1 for NMP-Ar and NMP-Kr, respectively

Reply to comment on the paper by Davies et al. “Resolving MISS conceptions and misconceptions: A geological approach to sedimentary surface textures generated by microbial and abiotic processes”

We thank Noffke (2017) for her comment and for providing an opportunity to clarify our classification of “sedimentary surface textures”. We accord great credit to Dr. Noffke and other dedicated researchers whose detailed work has brought microbially induced sedimentary structures (MISS) to the widespread attention of geoscientists. However, we stand by our assertion that attributing structures observed in practical field and laboratory studies to processes of formation is much more problematic than Noffke (2017) indicates. Indeed, points in the Comment confirm the need for a classification system that categorises the degree of certainty attributed to a given interpretation. We stress that our paper was not designed as a critique of previous studies of MISS but rather was designed to encourage a reasonable assessment of uncertainty in assigning sedimentary surface textures to physical processes or to MISS

Primary accumulation in the Soviet transition

The Soviet background to the idea of primary socialist accumulation is presented. The mobilisation of labour power and of products into public sector investment from outside are shown to have been the two original forms of the concept. In Soviet primary accumulation the mobilisation of labour power was apparently more decisive than the mobilisation of products. The primary accumulation process had both intended and unintended results. Intended results included bringing most of the economy into the public sector, and industrialisation of the economy as a whole. Unintended results included substantial economic losses, and the proliferation of coercive institutions damaging to attainment of the ultimate goal - the building of a communist society

Resolving MISS conceptions and misconceptions: A geological approach to sedimentary surface textures generated by microbial and abiotic processes

The rock record contains a rich variety of sedimentary surface textures on siliciclastic sandstone, siltstone and mudstone bedding planes. In recent years, an increasing number of these textures have been attributed to surficial microbial mats at the time of deposition, resulting in their classification as microbially induced sedimentary structures, or MISS. Research into MISS has developed at a rapid rate, resulting in a number of misconceptions in the literature. Here, we attempt to rectify these MISS misunderstandings. The first part of this paper surveys the stratigraphic and environmental range of reported MISS, revealing that contrary to popular belief there are more reported MISS-bearing rock units of Phanerozoic than Precambrian age. Furthermore, MISS exhibit a pan-environmental and almost continuous record since the Archean. Claims for the stratigraphic restriction of MISS to intervals prior to the evolution of grazing organisms or after mass extinction events, as well as claims for the environmental restriction of MISS, appear to result from sampling bias. In the second part of the paper we suggest that raised awareness of MISS has come at the cost of a decreasing appreciation of abiotic processes that may create morphologically similar features. By introducing the umbrella term ‘sedimentary surface textures’, of which MISS are one subset, we suggest a practical methodology for classifying such structures in the geological record. We illustrate how elucidating the formative mechanisms of ancient sedimentary surface textures usually requires consideration of a suite of sedimentological evidence from surrounding strata. Resultant interpretations, microbial or non-microbial, should be couched within a reasonable degree of uncertainty. This approach recognizes that morphological similarity alone does not constitute scientific proof of a common origin, and reinstates a passive descriptive terminology for sedimentary surface textures that cannot be achieved with the current MISS lexicon. It is hoped that this new terminology will reduce the number of overly sensational and misleading claims of MISS occurrence, and permit the means to practically separate initial observation from interpretation. Furthermore, this methodology offers a scientific approach that appreciates the low likelihood of conclusively identifying microbial structures from visual appearance alone, informing the search for true MISS in Earth's geological record and potentially on other planetary bodies such as Mars

Predicting Geographic Variation in Cutaneous Leishmaniasis, Colombia

Predicting Geographic Variation in ACL, Colombi