Astrochemistry
Programme

Astrochemistry

The Dutch Astrochemistry Network is funded by the The Netherlands Organisation for Scientific Research, NWO, to study the origin and evolution of molecules in space. This highly interdisciplinary programme combines astrochemical and astrophysical experiments, quantum chemical calculations, laboratory spectroscopy of astronomically relevant species and modeling and observations of astronomical sources. The Network has defined a highly integrated and coherent science programme on gas-phase chemistry, solid-state chemistry, interstellar polycyclic aromatic hydrocarbon molecules, and astrobiology

Vacancies Dutch Astrochemistry Network

We currently have 12 vacancies for 4-yrs PhD positions (starting as soon as possible) and one 3-yrs Postdoc position (starting in 2018).

To fill the open PhD positions, we are looking for enthusiastic persons with a (recent) Master degree in astronomy, physics or chemistry, interests in astrochemistry and specific background as indicated with the project titles listed below. Good communication skills in the English language are essential.

Interested students can request more details by contacting the PI and co-Is of the listed projects. Applications for specific positions should be sent directly to these PI/Co-Is, and contain a short letter of motivation, CV and names of two persons who are willing to provide letters of recommendation.

Applications are accepted until the vacancies are filled.
Depending on the project, we aim for starting dates already this Spring, but not later than 01.09.2017.

The Gaseous Molecular Universe

PROJECT 1: 4 yrs PhD position
PHOTO-ABSORPTION AND DISSOCIATION OF CH AND CARBON BASED RADICALS
Prof. Wim Ubachs (Free University Amsterdam), w.m.g.ubachs@vu.nl in collaboration with Prof. Harold Linnartz (Leiden Observatory), linnartz@strw.leidenuniv.nl

The goal of the project is to investigate the electronic photo-absorption spectrum of the CH radical to construct a full dissociation cross section under interstellar conditions; this will be achieved by combining experiment with CSE-modeling. The advanced experimental expertise, ranging from laser development, and plasma chemistry, to a variety of sensitive detection techniques (CRD, REMPI, VUV) of the Amsterdam LaserLaB team will be employed for these studies that will also focus on the analysis of gas phase spectra of larger carbon based molecular species. Novel techniques in the VUV (nonlinear crystals, Fourier-transform VUV, and synchrotron radiation) will be applied to access the higher lying quantum states of dissociative nature in small and larger carbon-based molecules. It is the intention of the team to combine the experimental and modeling studies with astronomical observations to establish constraints on the abundance of molecules as possible carriers of “Diffuse Interstellar Bands”, and ultimately to find matches with DIBs.

The candidate is an experimental physicist or physical chemist.

PROJECT 2: 3 yrs Postdoc position (starting 2018)
PROTOSTELLAR AND PROTOPLANETARY DISK CHEMISTRY; FROM BASIC DATA TO ASTROCHEMICAL MODELS
Prof. Ewine van Dishoeck (Leiden Observatory), ewine@strw.leidenuniv.nl

The JWST spectra of protostars and disks to be obtained with the MIRI and NIRSPEC instruments in guaranteed time programs co-led by van Dishoeck will be full of mid-infrared lines of atoms and molecules. The 3-year postdoc will develop non-LTE excitation models of small molecules such as CO2, CH4, NH3 to analyze the JWST spectra and infer abundances and physical parameters, implementing collisional rate coefficients obtained by DAN II partners. In addition, a full excitation model of OH taking into account the wavelength dependent photodissociation of H2O into OH(v,J), as well as state-to-state chemical reactions, will be built. This model is highly relevant for interpreting observations of bow shocks at the tip of outflows and disks, and is made possible thanks to unique data on these processes computed by DAN II collaborators. Finally, the importance of branching ratios to different products in the photodissociation of complex molecules in gas and ice chemistry will be investigated in sensitivity analyses. This project will form a two-way bridge between astronomy and chemical physics.

The candidate is an experienced astrochemical modeler.

PROJECT 3: 4 yrs PhD position
ROTATION-VIBRATION INELASTIC COLLISION RATES OF POLY ATOMIC MOLECULES
Prof. Gerrit Groenenboom (Radboud University Nijmegen), gerritg@theochem.ru.nl

Instruments on board the James Webb Space Telescope will cover the range of 0.6-28.5 mm, allowing the observation of molecules such as CO2, HCCH, and CH4 through vibrational transitions. These are key molecules for the study of protoplanetary disks and other astrochemical environments. Extracting molecular abundances, temperatures, and densities, requires rate constants for inelastic collision of these molecules with H2, He, and H. Theory has provided such constants for rotational inelastic collisions, but little is known for vibrationally inelastic processes. We propose to compute potentials and ro-vibrationally inelastic collision rates for these molecules. Such calculations are very demanding and we propose a number of techniques to alleviate this problem for the calculation of the potentials as well as the scattering calculations. We aim to make results of lowlevel calculations available for sensitivity analysis of the astrochemical models first, and to either push the accuracy or treat additional systems based on the result of the analysis.

The candidate is a computational chemist/physicist.

PROJECT 4: 4 yrs PhD position
IT TAKES TWO TO TANGO; BI-MOLECULAR (HALF) COLLISIONS OF ASTROCHEMICAL RELEVANCE
Prof. David Parker (Radboud University Nijmegen), parker@science.ru.nl in collaboration with Prof. Bas van de Meerakker (Radboud University Nijmegen), B.vandeMeerakker@science.ru.nl

When two molecules collide, or a larger molecule breaks into two molecules, they leave each other in a highly correlated fashion, spinning off, for example, in equal and opposite directions. These so-called product pair correlations, which are just becoming possible to measure, provide excellent probes of the present theoretical understanding of molecular dynamics that underlies all models of astrochemical observation. In this proposal four years of funding for a PhD position are requested for research centered on this topic. Two of the PhD years will be devoted to cold collisions, where Nijmegen is a leading center in this research using Stark and Zeeman decelerators. Velocity map imaging, invented in Nijmegen, has a key role in our collision and photodissociation work. We are interested in applying our advanced research tools in fundamental research projects directly relevant to astrochemistry problems. We offer three research lines: a) Controlled cold collisions of NH3 with H2, for testing molecule-molecule scattering theory to the limit; b) State-to-state inelastic scattering of formaldehyde with He and H2, measuring differential cross sections that are highly sensitive tests of current theory on this system; and c) VUV photodissociation branching ratio studies of methanol, a long-standing and particularly important but challenging measurement.

The candidate is an experimental physicist or physical chemist.

The Icy Universe

PROJECT 5: 4 yrs PhD position
CIRCUMSTELLAR ICE AND SNOW LINES - PHOTOCHEMISTRY AT THE EDGE
Dr. Michiel Hogerheijde (Leiden Observatory), michiel@strw.leidenuniv.nl in collaboration with Prof. Harold Linnartz (Leiden Observatory), linnartz@strw.leidenuniv.nl

There is currently no good model that explains the gas phase abundances of large complex molecules in cold and dense areas in space where thermal desorption from ices cannot occur. Photodesorption has been proposed as a non-thermal desorption mechanism, but experiments show that especially larger species tend to dissociate upon UV irradiation rather than evaporate intactly. This prohibits a smooth transition from the solid state to the gas phase. Instead, the gas phase may be enriched with radical fragments. Indirect photodesorption, i.e., photo-induced co-desorption, may offer an alternative pathway for a smooth sublimation process: the soft desorption takes place after interaction of a non-excited molecule with another photo-excited species. It is also possible that the excess energy released through a photochemical reaction forms a local ‘hot spot’, sufficiently warm to ‘thermally’ desorb a molecule. This ‘hot spot desorption’ is known as chemisorption.

The goal of this project is to find out which of these processes are at play, by observationally characterizing spatially resolved molecule maps of protoplanetary disks on either side of photoinduced snow lines, and experimentally determining of the physics and chemistry of UVprocessed ices. The focus in the laboratory will be on astronomically relevant (that is to say: mixed) ices. It will guide the interpretation of the observations by identifying the UV-produced species and quantifying their production rates. Our combined observational and experimental approach aims to unravel the mechanisms that link the solid state and the gas phase.

The candidate is an experimental physicist, physical chemist, astronomical instrumentalist with interest to spend 50% of his/her time on astronomical observations (ALMA).

PROJECT 6: 4 yrs PhD position
MOLECULAR COMPLEXITY IN INTERSTELLAR ICES - A COMBINED EXPERIMENTAL / THEORETICAL STUDY
Prof. Harold Linnartz (Leiden Observatory), linnartz@strw.leidenuniv.nl in collaboration with Dr. Herma Cuppen (Radboud University Nijmegen), h.cuppen@science.ru.nl.

Astronomical observations show that the interstellar medium contains a large number of complex organic molecules (COMs). The steady progress in laboratory, observational and theoretical work has made clear that these COMs are efficiently formed on the surface of icy dust grains. Although energetic processing of these surfaces was thought to be the main mechanism to the formation of COMs in space, recent observations in dense molecular clouds have challenged this hypothesis. An alternative route to molecular complexity is the nonenergetic surface atom addition and radical recombination reactions taking place under dark interstellar cloud conditions.

This project is about a systematic experimental and theoretical study simulating the solid state processes at play in dark clouds, where thermal processing can be ruled out completely and photo-processing is limited to the exposure by cosmic rays induced UV-photons. In the laboratory, cryogenic ultra-high vacuum setups will be used. These systems are capable of studying hydrogenation and other atom- and radical-addition reactions in interstellar ice analogues. The laboratory results will be supported by sophisticated models used to derive molecular parameters (e.g., reaction rates and barriers). The models will be able to reproduce laboratory data and can be used as input in astrochemical models to extend the experimental findings to astronomical timescales. The reaction networks and reaction efficiencies derived in this way will be used to compare with astronomical data.

The candidate is an experimental physicist, physical chemist with strong interest in astrochemical modeling.

PROJECT 7: 4 yrs PhD position
MOBILITY AND RESTRUCTURING IN INTERSTELLAR ICES
Dr. Herma Cuppen (Radboud University Nijmegen), h.cuppen@science.ru.nl in collaboration with Dr. Britta Redlich (Radboud Universiy Nijmegen), b.redlich@science.ru.nl

The new Atacama Large Millimeter Array and the soon-to-be-launched James Webb Space Telescope are expected to give us an unprecedented view of complex molecules and ices in various astrophysical environments. The analysis of these data will require much more elaborate, and more diverse, gas-grain astrochemical models than have been developed so far. A crucial process in these models is the diffusion of reacting species to meet and react. Little data on diffusion rates is however available, in particular for bulk diffusion, which becomes important in warmer regions and is thought to be the driving force behind complex molecule formation in hot cores. Here we propose to use computational techniques to study (i) surface diffusion of reactive species which are technically more challenging to treat, but crucial in understanding surface chemistry, (ii) bulk diffusion using metadynamics simulations, a technique that has not been used in astrochemistry but has great potential in solving these type of questions, and (iii) restructuring of ices by mimicking pump-probe experiments at the IR and THz free electron laser FELIX experiments by molecular dynamics simulations. The advantage of using a free electron laser is the possibility of resonantly pumping specific modes, which is a selective probe for the local structure of the ice. Moreover, the short pulse defines a clear starting point of the process and allows for observation of processes with a very high time resolution. Deliverables of this project will be directly transferable to gas-grain models and aid in the mechanistic understanding of bulk diffusion.

The candidate is a computational chemist/physicist.

PROJECT 8: 4 yrs PhD position
VELOCITY MAP IMAGING AT ICY SURFACES
Prof. David Parker (Radboud University Nijmegen), parker@science.ru.nl

A 4-year PhD is requested to study photodesorption and molecular beam scattering at methanol ice surfaces. A new velocity map imaging apparatus with ice surface capabilities will be used which was constructed for a pilot project supported by the NWO CW TOP project “Imaging Astrochemistry”. This apparatus is just now starting to yield exciting results on laser desorption at O2 ice surfaces. By the time the DAN-II project begins, scattering of CO from ice surfaces should be demonstrated, and the first publication on singlet O2 generation at O2 ice surfaces should be submitted. DAN-II will allow this state-of-the-art apparatus to be further developed and employed for astrochemical goals of high relevance, particularly on systematic VUV desorption studies on the complex methanol ice system. The work plan involves one year of training on the new apparatus, followed by growth and characterization of the methanol surface. The long-term goal is a full dynamics study based on detection of all desorption products for desorption wavelengths from the UV to 100 nm. Realistically, desorption at the VUV absorption peaks and detection of the major products in the order: H, CO, CH3, H2, and CH3O can be expected. In the fourth year all articles will be finished and the thesis prepared.

The candidate is an experimental physicist or physical chemist.

The Aromatic Universe

PROJECT 9: 4 yrs PhD position
HIGH RESOLUTION VIBRATIONAL AND ELECTRONIC SPECTROSCOPY OF THE ISOLATE AROMATIC UNIVERSE
Prof. Wybren-Jan Buma (University of Amsterdam), W.J.Buma@uva.nl, in collaboration with Dr. Anouk Rijs (Radboud University Nijmegen), a.rijs@science.ru.nl.

Currently, the analysis and interpretation of astronomical data relies on PAH models that use low-resolution, laboratory spectroscopic data obtained under conditions that are not compatible with conditions in space, and on theoretical calculations at a level that require post-processing to obtain agreement with experimental data. The present project will use recently developed laser spectroscopic techniques to acquire high-resolution infrared absorption spectra of isolated, cold PAHs and related compounds of astronomically relevant sizes in all AIB wavelength regions. These experimental spectra will be used to validate state-of-the-art quantum chemical calculations and extend such calculations to large PAHs. This combination also allows us to (i) show how the vibrational signatures of PAHs are affected by anharmonicity and Fermi resonances, (ii) provide much-needed means to compare the relative intensities of AIBs in different wavelength regions, (iii) elucidate how substituents and chemical modifications work through in spectral signatures, and (iv) pave the way for the identification of grandPAHs. At the same time, these studies will provide high-resolution electronic excitation spectra that are of interest in the context of identifying the carriers of DIBs. Overall, the project will lead to PAH models that are far superior to the ones employed at the moment, and thereby to a far better understanding of the origin and evolution of interstellar PAHs and of their role in the universe.

The candidate is an experimental physicist, physical chemist.

PROJECT 10: 4 yrs PhD position
REACTION OF PAHs: A ROUTE TO CHEMICALLY COMPLEX MOLECULES?
Prof. Matthias Bickelhaupt (Free University, Amsterdam), f.m.bickelhaupt@vu.nl, in collaboration with Dr. Ingmar Swart (University Utrecht), I.Swart@uu.nl.

Our understanding of Polycyclic aromatic hydrocarbons (PAHs) chemistry under astrochemically relevant conditions and therefore also its contribution to the formation of chemically complex molecules, is still very limited. PAHs may undergo reactions in the gas phase, as well as on surfaces of interstellar dust particles. In the latter case, the surface may have a profound influence on the chemical reactivity of PAHs. For example, it is well-known that on earth surfaces containing transition metals (especially Fe) can catalyze chemical reactions of PAHs. Furthermore, in both the gas-phase and on surfaces, the geometric structure of the PAHs (e.g. the curvature) may make additional types of reactions, and therefore products, favorable. Using a combination of scanning probe microscopy and density functional theory we will study reactions of planar and curved PAHs on water ice covered surfaces under astrochemically relevant conditions in a controlled step-by-step fashion. The comprehensive characterization of all species involved in PAH chemistry, including reactive reaction intermediates, will reveal how PAHs contribute to the formation of chemically complex molecules. This projects also serves to enhance coherence within the aromatic universe theme of DAN II: It provides guidelines and support for the other projects. It does so by addressing the underlying physical factors behind structure, spectra and reactive processes through experimental and quantum theoretical methods.

The candidate is a theoretical chemist, computational chemist/physicist.

PROJECT 11: Two 4 yrs PhD positions
PHOTO-PROCESSING, REACTIVITY AND SPECTROSCOPIC CHARACTERISTICS OF LARGE PAHS AND THEIR DERIVATIVES
Prof. Jos Oomens, (Radboud University Nijmegen), J.Oomens@science.ru.nl Prof. Xander Tielens (Leiden Observatory), tielens@strw.leidenuniv.nl

Combination of tandem mass spectrometry with laser spectroscopy methods has been a fruitful marriage of techniques in the study of polyaromatic molecules (PAHs) in the context of astrochemical questions. It has allowed for the recording of IR spectra of ionized PAHs in complete isolation of the gas phase (i.e. no matrix) and for the investigation of UV-induced breakdown pathways in terms of m/z values of the resulting reaction products. Here, we propose to advance these methods to address

  1. the spectroscopic properties of PAHs of astrochemically relevant size (50+ C-atoms)
  2. the spectroscopy and structure of their breakdown products
  3. their gas-phase spectra in the UV/vis wavelength range

Several technical advances and upgrades are described that will be explored to overcome experimental limitations that have thus far restricted the size range of PAHs studied. The spectra obtained in these studies will be the first experimental gas-phase spectra of PAHs in this important size range and may serve as critical benchmarks for comparison with interstellar spectra but also with DFT calculated spectra. The project will be carried out by two PhD students in parallel, one at the Radboud University Nijmegen and one at Leiden University.

The candidate is an experimental physicist, physical chemist with interests in astrochemical modeling.

PROJECT 12: 4 yrs PhD position
THE REACTION DYNAMICS OF IONIC AND NEUTRAL PAHS
Dr. Annemieke Petrignani (University of Amsterdam), a.petrignani@uva.nl

This project aims to investigate the PAH reaction rates and dynamics, validate theoretical calculations, and thereby incorporate new insights and findings in astronomical PAH models. We propose to determine the kinetic parameters of PAHs from the fragmentation and branching ratios as function of internal energy, providing a means to extrapolate laboratory measurements to interstellar environments. We propose to perform laboratory studies supported by theoretical studies to investigate the branching ratios in the fragmentation of PAHs, the energy distribution among the fragments and their internal energy, both for neutral and ionic species. The newly gained findings will be incorporated into state-of-the-art astronomical PAH models.

The candidate is an experimental physicist or physical chemist.

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