Beyond the Born-Oppenheimer approximation: high-resolution overtone spectroscopy of H2D+ and D2H+

Transitions to overtone 2v2 and 2v3, and combination v2 + v3 vibrations in jet-cooled H2D+ and D2H+ molecular ions have been measured for the first time by high-resolution IR spectroscopy. The source of these ions is a pulsed slit jet supersonic discharge, which allows for efficient generation, rotational cooling, and high frequency (100 KHz) concentration modulation for detection via sensitive lock-in detection methods. Isotopic substitution and high-resolution overtone spectroscopy in this fundamental molecular ion permit a systematic, first principles investigation of Born–Oppenheimer "breakdown" effects due to large amplitude vibrational motion as well as provide rigorous tests of approximate theoretical methods beyond the Born–Oppenheimer level. The observed overtone transitions are in remarkably good agreement (<0.1 cm–1) with non-Born–Oppenheimer ab initio theoretical predictions, with small but systematic deviations for 2v2, 2v + 3v, and 2v3 excited states indicating directions for further improvement in such treatments. Spectroscopic assignment and analysis of the isotopomeric transitions reveals strong Coriolis mixing between near resonant 2v3 and 2v + 3v vibrations in D2H+. Population-independent line intensity ratios for transitions from common lower states indicate excellent overall agreement with theoretical predictions for D2H+, but with statistically significant discrepancies noted for H2D+. Finally, H2D+ versus D2H+ isotopomer populations are analyzed as a function of D2/H2 mixing ratio and can be well described by steady state kinetics in the slit discharge expansion

Observations of conduction driven evaporation in the early rise phase of solar flares

&lt;p&gt;&lt;b&gt;Context:&lt;/b&gt; The classical flare picture features a beam of electrons, which were accelerated in a site in the corona, hitting the chromosphere. The electrons are stopped in the dense chromospheric plasma, emitting bremsstrahlung in hard X-rays. The ambient material is heated by the deposited energy and expands into the magnetic flare loops, a process termed chromospheric evaporation. In this view hard X-ray emission from the chromosphere is succeeded by soft-X-ray emission from the hot plasma in the flare loop, the soft X-ray emission being a direct consequence of the impact of the non-thermal particle beam. However, observations of events exist in which a pronounced increase in soft X-ray emission is observed minutes before the onset of the hard X-ray emission. Such pre-flare emission clearly contradicts the classical flare picture.&lt;/p&gt; &lt;p&gt;&lt;b&gt;Aims:&lt;/b&gt; For the first time, the pre-flare phase of such solar flares is studied in detail. The aim is to understand the early rise phase of these events. We want to explain the time evolution of the observed emission by means of alternative energy transport mechanisms such as heat conduction.&lt;/p&gt; &lt;p&gt;&lt;b&gt;Methods:&lt;/b&gt; RHESSI events displaying pronounced pre-flare emission were analyzed in imaging and spectroscopy. The time evolution of images and full sun spectra was investigated and compared to the theoretical expectations from conduction driven chromospheric evaporation. Results. The pre-flare phase is characterized by purely thermal emission from a coronal source with increasing emission measure and density. After this earliest phase, a small non-thermal tail to higher energies appears in the spectra, becoming more and more pronounced. However, images still only display one X-ray source, implying that this non-thermal emission is coronal. The increase of emission measure and density indicates that material is added to the coronal region. The most plausible origin is evaporated material from the chromosphere. Energy provided by a heat flux is capable of driving chromospheric evaporation. We show that the often used classical Spitzer treatment of the conductive flux is not applicable. The conductive flux is saturated. During the preflare-phase, the temperature of the coronal source remains constant or increases. Continuous heating in the corona is necessary to explain this observation.&lt;/p&gt; &lt;p&gt;&lt;b&gt;Conclusions:&lt;/b&gt; The observations of the pre-flare phase of four solar flares are consistent with chromospheric evaporation driven by a saturated heat flux. Additionally, continuous heating in the corona is necessary to sustain the observed temperature.&lt;/p&gt

Generation and orientation of organoxenon molecule H–Xe–CCH in the gas phase

We report on the first observation of the organoxenon HXeCCH molecule in the gas phase. This molecule has been prepared in a molecular beam experiment by 193 nm photolysis of an acetylene molecule on Xen clusters (¯n ≈ 390). Subsequently the molecule has been oriented via the pseudofirst-order Stark effect in a strong electric field of the polarized laser light combined with the weak electrostatic field in the extraction region of a time-of-flight spectrometer. The experimental evidence for the oriented molecule has been provided by measurements of its photodissociation. For comparison, photolysis of C₂H₂ on Arn clusters (¯n ≈ 280) has been measured. Here the analogous rare gas molecule HArCCH could not be generated. The interpretation of our experimental findings has been supported by ab initio calculations. In addition, the experiment together with the calculations reveals information on the photochemistry of the HXeCCH molecule. The 193 nm radiation excites the molecule predominantly into the 2¹∑⁺ state, which cannot dissociate the Xe-H bond directly, but the system evolves along the Xe-C coordinate to a conical intersection of a slightly non-linear configuration with the dissociative 1¹∏ state, which then dissociates the Xe-H bond

Deuterated hydrogen chemistry: Partition functions, Equilibrium constants and Transition intensities for the H3+ system

H3+ and the deuterated isotopomers are thought to play an important role in interstellar chemistry. The partition functions of H3+, D2H+ and D3+ are calculated to a temperature of 800 K by explicitly summing the ab initio determined rotation-vibration energy levels of the respective species. These partition functions are used to calculate the equilibrium constants for nine important reactions in the interstellar medium involving H3+ and its deuterated isotopomers. These equilibrium constants are compared to previously determined experimental and theoretical values. The Einstein A coefficients for the strongest dipole transitions are also calculated

Ring formation and hydration effects in electron attachment to misonidazole

This research was funded by CZECH SCIENCE FOUNDATION grant number 19-01159S; Czech Ministry of Education Youth and Sports via OP RDE Grant no. CZ.02.2.69/0.0/16_027/0008355; S.D. acknowledges funding from the FWF, Vienna (P30332).We study the reactivity of misonidazole with low-energy electrons in a water environment combining experiment and theoretical modelling. The environment is modelled by sequential hydration of misonidazole clusters in vacuum. The well-defined experimental conditions enable computational modeling of the observed reactions. While the NO- 2 dissociative electron attachment channel is suppressed, as also observed previously for other molecules, the OH- channel remains open. Such behavior is enabled by the high hydration energy of OH- and ring formation in the neutral radical co-fragment. These observations help to understand the mechanism of bio-reductive drug action. Electron-induced formation of covalent bonds is then important not only for biological processes but may find applications also in technology.publishersversionpublishe

A computed line list for the H2D+ molecular ion

A comprehensive, calculated line list of frequencies and transition probabilities for the singly deuterated isotopologue of H3+, H2D+, is presented. The line list, called ST1, contains over 22 million rotational-vibrational transitions occurring between more than 33 thousand energy levels; it covers frequencies up to 18500 cm-1. All energy levels with rotational quantum number, J, up to 20 are considered, making the line list useful for temperatures up to at least 3000 K. About 15% of these levels are fully assigned with approximate rotational and vibrational quantum numbers. The list is calculated using a previously proposed, high accuracy, ab initio model and consistency checks are carried out to test and validate the results. These checks confirm the accuracy of the list. A temperature-dependent partition function, valid over a more extended temperature range than those previously published, and cooling function are presented. Temperature-dependent synthetic spectra in the frequency range 0 - 10000 cm-1 are also given.Comment: 7 pages, 3 figures, 5 table

Svestka's Research: Then and Now

Zdenek Svestka's research work influenced many fields of solar physics, especially in the area of flare research. In this article I take five of the areas that particularly interested him and assess them in a "then and now" style. His insights in each case were quite sound, although of course in the modern era we have learned things that he could not readily have envisioned. His own views about his research life have been published recently in this journal, to which he contributed so much, and his memoir contains much additional scientific and personal information (Svestka, 2010).Comment: Invited review for "Solar and Stellar Flares," a conference in honour of Prof. Zden\v{e}k \v{S}vestka, Prague, June 23-27, 2014. This is a contribution to a Topical Issue in Solar Physics, based on the presentations at this meeting (Editors Lyndsay Fletcher and Petr Heinzel