New observations of stratospheric N2O5

The unequivocal detection of N2O5 in the stratosphere was reported by Toon et al. based on measurements of the absorption by the N2O5 bands at 1246 and 1720/cm in solar occulation spectra recorded at sunrise near 47 S latitude by the Atmospheric Trace Molecule Spectroscopy (ATMOS) experiment during the Spacelab 3 (SL3) shuttle mission. Additional measurements and analysis of stratospheric N2O5 derived from the ATMOS/SL3 spectra are reported. The primary results are the detection and measurement of N2O5 absorption at sunset in the lower stratosphere, the inversion of a precise (approximately 10 percent) N2O5 sunrise vertical distribution between 25.5 and 37.5 km altitude, and the identification and measurement of absorption by the N2O5 743/cm band at sunrise. Assuming 4.32 x 10(sup -17) and 4.36 x 10(sup -17)/cm/molecule/sq cm respectively for the integrated intensities of the 1246 and 743/cm bands at stratospheric temperatures, retrieved volume mixing ratios in parts per billion by volume (ppbv) at sunrise (47 S latitude) are 1.32 + or - 0.34 at 37.5 km, 1.53 + or - 0.35 at 35.5 km, 1.63 + or - 0.36 at 33.5 km, 1.60 + or - 0.34 at 31.5 km, 1.43 + or - 0.30 at 29.5 km, 1.15 + or - 0.24 at 27.5 km, and 0.73 + or - 0.15 at 25.5 km. Retrieved VMRs in ppbv at sunset (30 N latitude) are 0.13 + or - 0.05 at 29.5 km, 0.14 + or - 0.05 at 27.5 km, and 0.10 + or - 0.04 at 25.5 km. Quoted error limits (1 sigma) include the error in the assumed band intensities (approximately 20 percent). Within the error limits of the measurements, the inferred mixing ratios at sunrise agree with diurnal photochemical model predictions obtained by two groups using current photochemical data. The measured mixing ratios at sunset are lower than the model predictions with differences of about a factor of 2 at 25 km altitude

The dark matter halo shape of edge-on disk galaxies - II. Modelling the HI observations: methods

This is the second paper of a series in which we attempt to put constraints on the flattening of dark halos in disk galaxies. For this purpose, we observe the HI in edge-on galaxies, where it is in principle possible to measure the force field in the halo vertically and radially from gas layer flaring and rotation curve decomposition respectively. To calculate the force fields, we need to analyse the observed XV diagrams to accurately measure all three functions that describe the planar kinematics and distribution of a galaxy: the radial HI surface density, the rotation curve and the HI velocity dispersion. In this paper, we discuss the improvements and limitations of the methods previously used to measure these HI properties. We extend the constant velocity dispersion method to include determination of the HI velocity dispersion as a function of galactocentric radius and perform extensive tests on the quality of the fits. We will apply this 'radial decomposition XV modelling method' to our HI observations of 8 HI-rich, late-type, edge-on galaxies in the third paper of this series.Comment: Accepted for publication by Astronomy & Astrophysics. For a higher resolution version see http://www.astro.rug.nl/~vdkruit/jea3/homepage/12566.pd

Velocity Map Imaging of the Single Ionization of Molecular Iodine

Single ionization in molecules is a critical first step in many higher order process, however it remains poorly understood even in simple diatomic systems. Velocity map imaging of ion fragments produced from dissociation after single ionization provide access to the kinetic energy released (KER) during dissociation. In this thesis, I will present two experimental studies of the single ionization of diatomic iodine. In a long wavelength scan spanning 400-800 nm the single ionization of I2 is found to have a contribution from deeply bound 5s electrons. In the I + I+ dissociation channel, much of the measured KER is inconsistent with ionization from the X, A, and B states of I2+ implying ionization from deeper orbitals. A pump-probe Fourier transform technique shows X and A state modulation is only seen for low KER dissociation through the B state. A narrow wavelength scan of the single ionization of I2 around the 530 nm one-photon B state resonance shows a strong enhancement in the branching ratio for inner orbital ionization while a weaker peak for outer orbital ionization occurs at a slightly different wavelength. The branching ratio from double ionization as a function of wavelength closely matches the branching ratio of single ionization of deep orbitals, implying that excitation of molecular ions generally comes about through inner orbital ionization. Current molecular ionization theory suggests that the least bound outer electrons will play a significant role in the single ionization of molecules. These findings are inconsistent with such ionization theories

Methods for deriving temperature profiles of Mars from OH Meinel airglow observations

Observations of the OH Meinel Band airglow emission from vibrationally excited ground electronic state OH radicals have long been used to gain valuable information about the dynamics and state of the upper atmosphere of Earth. In this work, we attempt to develop methods for use in the Martian atmosphere. The middle Martian atmosphere is a layer of rich dynamics, such as planetary and gravity waves, however it is not well understood. It is important to develop methodologies to aid in achieving a better understanding of this part of the Martian atmosphere. In this work, methods for the retrieval of temperatures and OH Meinel Band volume emission rates from possible future limb observations of the Martian atmosphere are developed and compared with the goal of determining general instrument requirements for the observation and analysis of yet to be detected emissions of the Martian nighttime OH Meinel Band airglow. To this end, a non-linear fitting algorithm is developed to fit modelled wavelength bin radiance spectra to observations to recover temperatures and total vibrational level volume emission rates. Three different approaches for retrieval are developed: an Onion Peeling approach, a Global Optimization approach and an approach using Derived Absolute Wavelength Bin Radiance Spectra. The Global Optimization method is found to be the most robust and is used to estimate the order of magnitude of instrument optical properties necessary for the detection of the emission and the retrieval of temperatures and emission rates. The results of this investigation will advance the application of remote sensing techniques to planetary atmospheres. The developed retrieval methods are flexible and, as such, are not limited in application to the Martian OH Meinel Band airglow. They can be used on any planet where emissions of OH Meinel Band airglow have been observed, such as Venus

Optical Characterization of Component Wear and Near-Field Plasma of the Hermes Thruster

Optical emission spectral (OES) data are presented which correlate trends in sputtered species and the near-field plasma with the Hall-Effect Rocket with Magnetic Shielding (HERMeS) thruster operating condition. The relative density of singly-ionized xenon (Xe II) is estimated using a collisional-radiative model. OES data were collected at three radial and several axial locations downstream of the thruster's exit plane. These data were deconvolved to show the structure for the near-field plasma as a function of thruster operating condition. The magnetic field is shown to have a much greater affect on plasma structure than the discharge voltage with the primary ionization/acceleration zone boundary being similar for all nominal operating voltages at constant power. OES measurement of sputtered boron shows that the HERMeS thruster is magnetically shielded across its operating envelope. Preliminary assessment of carbon sputtered from the keeper face suggest it increases significantly with operating voltage, but the uncertainty associated with these measurements is very high

Light-matter interactions

Understanding light-matter interaction is important to control the electron and nuclear dynamics of quantum-mechanical systems. The present work investigates this in the form of angular dependent tunnel ionization and different control mechanisms for nuclear, electron and coupled dynamics. With the help of close collaboration with experimental groups several control mechanisms could be examined and explained. The refined methods and models for these studies can be expanded for different experiments or more general concepts. The first part of this thesis focuses on tunnel ionization as one of the fundamental quantum-mechanical light-matter interactions while the second and third part investigates the control of nuclear and electron dynamics in depth. The angular dependent tunnel ionization of small hydrocarbons and the impact of their field dressed orbitals are researched in chapter 3. Advanced quantum chemical methods are used to explain experimental findings that could not be recognized by only looking at the Highest Occupied Molecular Orbital (HOMO). The so studied molecules show the importance to consider field dressed instead of field free orbitals to understand the light-matter interaction, to replicate experimental findings with theoretical models and to predict the behavior of different molecules. The influence of Rydberg character in virtual orbitals, that can become populated in a field dressed picture, can explain the difference in the angular dependent tunnel ionization for two similar derivates of Cyclohexadiene (CHD) and the lobed structure for C2H4 . This chapter also shows the success of adapting a previous used model for diatomic systems to polyatomic systems. The second part (chapter 4) investigates the deprotonation and isomerization reaction of acetylene (C2H2) and allene (C3H4) and the potential control with laser pulses over theses reaction. The first control mechanism utilizes the light field to suppress the reaction barrier, which allows molecules with lower energy to undergo isomerization and therefore increase the rate of the reaction. The second scheme controls the asymmetry of the reaction, so that either the left to right or right to left isomerization is preferred. This control is exercised by directly manipulating the nuclear wave packet with the Carrier–Envelope–Phase (CEP) of the laser pulse. The mechanism relies on forming a superposition of different normal modes that are excited by different means and therefore have a phase difference. One or more normal modes are excited by the light field and get the CEP imprinted in their phase while the other important normal modes are indirectly excited by the ionization process. This enables directional control of the nuclear dynamics in symmetric molecules. The concept of forming the superposition is general enough to be used in different reactions and molecules. In the last part (chapter 5) the control of electron dynamics with laser pulses is studied. The test case is the selective population of dressed states (SPODS) in the potassium dimer (K2). There a first pulse will populate an electronic superposition between the ground and first excited state. Depending on the relative phase of the second pulse to the oscillating dipole created by the electronic wave packet, the upper or lower dressed state will be populated. Excitation from the two different dressed states leads to two distinguishable final states. Although the scheme focuses on the control of the electron dynamics, the whole mechanism is also heavily influenced by the associated nuclear dynamics

Light-matter interactions

Understanding light-matter interaction is important to control the electron and nuclear dynamics of quantum-mechanical systems. The present work investigates this in the form of angular dependent tunnel ionization and different control mechanisms for nuclear, electron and coupled dynamics. With the help of close collaboration with experimental groups several control mechanisms could be examined and explained. The refined methods and models for these studies can be expanded for different experiments or more general concepts. The first part of this thesis focuses on tunnel ionization as one of the fundamental quantum-mechanical light-matter interactions while the second and third part investigates the control of nuclear and electron dynamics in depth. The angular dependent tunnel ionization of small hydrocarbons and the impact of their field dressed orbitals are researched in chapter 3. Advanced quantum chemical methods are used to explain experimental findings that could not be recognized by only looking at the Highest Occupied Molecular Orbital (HOMO). The so studied molecules show the importance to consider field dressed instead of field free orbitals to understand the light-matter interaction, to replicate experimental findings with theoretical models and to predict the behavior of different molecules. The influence of Rydberg character in virtual orbitals, that can become populated in a field dressed picture, can explain the difference in the angular dependent tunnel ionization for two similar derivates of Cyclohexadiene (CHD) and the lobed structure for C2H4 . This chapter also shows the success of adapting a previous used model for diatomic systems to polyatomic systems. The second part (chapter 4) investigates the deprotonation and isomerization reaction of acetylene (C2H2) and allene (C3H4) and the potential control with laser pulses over theses reaction. The first control mechanism utilizes the light field to suppress the reaction barrier, which allows molecules with lower energy to undergo isomerization and therefore increase the rate of the reaction. The second scheme controls the asymmetry of the reaction, so that either the left to right or right to left isomerization is preferred. This control is exercised by directly manipulating the nuclear wave packet with the Carrier–Envelope–Phase (CEP) of the laser pulse. The mechanism relies on forming a superposition of different normal modes that are excited by different means and therefore have a phase difference. One or more normal modes are excited by the light field and get the CEP imprinted in their phase while the other important normal modes are indirectly excited by the ionization process. This enables directional control of the nuclear dynamics in symmetric molecules. The concept of forming the superposition is general enough to be used in different reactions and molecules. In the last part (chapter 5) the control of electron dynamics with laser pulses is studied. The test case is the selective population of dressed states (SPODS) in the potassium dimer (K2). There a first pulse will populate an electronic superposition between the ground and first excited state. Depending on the relative phase of the second pulse to the oscillating dipole created by the electronic wave packet, the upper or lower dressed state will be populated. Excitation from the two different dressed states leads to two distinguishable final states. Although the scheme focuses on the control of the electron dynamics, the whole mechanism is also heavily influenced by the associated nuclear dynamics

Extracting the Dark Matter Profile of a Relaxed Galaxy Cluster

Knowledge of the structure of galaxy clusters is essential for an understanding of large scale structure in the universe, and may provide important clues to the nature of dark matter. Moreover, the shape of the dark matter distribution in the cluster core may offer insight into the structure formation process. Unfortunately, cluster cores also tend to be the site of complicated astrophysics. X-ray imaging spectroscopy of relaxed clusters, a standard technique for mapping their dark matter distributions, is often complicated by the presence of cool components in cluster cores, and the dark matter profile one derives for a cluster is sensitive to assumptions made about the distribution of this component. In addition, fluctuations in the temperature measurements resulting from normal statistical variance can produce results which are unphysical. We present here a procedure for extracting the dark matter profile of a spherically symmetric, relaxed galaxy cluster which deals with both of these complications. We apply this technique to a sample of galaxy clusters observed with the Chandra X-ray Observatory, and comment on the resulting mass profiles. For some of the clusters we compare their masses with those derived from weak and strong gravitational measurements.Comment: final version to match accepted ApJ version; 29 page

Development and Construction of a new Photoelectron Imaging Spectrometer for Studying the Spectroscopy and Ultrafast Dynamics of Molecular Anions

We present a detailed account of the development, construction, and commissioning of a new experiment for studying the spectroscopy and ultrafast dynamics of molecular anions in the gas phase. The new instrument incorporates: an electrospray ionisation source, which is capable of generating a vast class of molecular anions; a Wiley-McLaren time-of-flight mass spectrometer; and a compact photoelectron imaging arrangement for anions, which negates the use of pulsed high voltages. We use this instrument in conjunction with a femtosecond laser system to perform the first ultrafast time-resolved photoelectron imaging experiments on molecular anions generated through electrospray ionisation. A method for reconstructing three dimensional charged particle distributions from their associated two dimensional projections on an imaging detector plane is described. This new method utilises: (1) onion-peeling in polar co-ordinates (POP) to perform the reconstruction; and (2) basis set concepts to significantly enhance the algorithms computational speed. We compare this new POP algorithm with other reconstruction algorithms, which shows that the method is as good as the benchmark pBASEX method in terms of accuracy. Importantly, we show that it is also computationally fast, allowing images to be reconstructed as they are acquired in a typical imaging experiment. Original work is presented which investigates the spectroscopy and ultrafast excited dynamics of the 7,7,8,8-tetracyanoquinodimethane (TCNQ) radical anion. The photoelectron spectrum of TCNQ– is measured at 3.1 eV, which is used to gain insight into the electronic structure and geometries of both the anion and neutral states. Time-resolved photoelectron imaging experiments explore the relaxation dynamics of its first excited 1 2B3u state, which we show undergoes internal conversion back to the 2B2g ground state on a timescale of 650 fs. Results also provide evidence of a wave packet motion on the excited state, which exhibits a characteristic frequency of 30 cm–1. Finally, we describe, for the first time, a formulism which allows ultrafast relaxation timescales to be extracted from the photoelectron angular distributions of isoenergetic photoelectron features. As an example, we use the time-resolved photoelectron angular distributions of a nearly isoenergetic feature in the photoelectron images of TCNQ–. From this model we extract a relaxation time for the 1 2B3u state, which quantitatively agrees with those extracted from fits to the features in the photoelectron spectra derived from the images

Bayesian modelling of the cool core galaxy group NGC 4325

We present an X-ray analysis of the radio-quiet cool-core galaxy group NGC 4325 (z=0.026) based on Chandra and ROSAT observations. The Chandra data were analysed using XSPEC deprojection, 2D spectral mapping and forward-fitting with parametric models. Additionally, a Markov chain Monte Carlo method was used to perform a joint Bayesian analysis of the Chandra and ROSAT data. The results of the various analysis methods are compared, particularly those obtained by forward-fitting and deprojection. The spectral mapping reveals the presence of cool gas displaced up to 10 kpc from the group centre. The Chandra X-ray surface brightness shows the group core to be highly disturbed, and indicates the presence of two small X-ray cavities within 15 kpc of the group core. The XSPEC deprojection analysis shows that the group has a particularly steep entropy profile, suggesting that an AGN outburst may be about to occur. With the evidence of prior AGN activity, but with no radio emission currently observed, we suggest that the group in in a pre-outburst state, with the cavities and displaced gas providing evidence of a previous, weak AGN outburst.Comment: 12 pages, 10 figures; accepted for publication in MNRA