Knife edge skimming for improved separation of molecular species by the deflector

A knife edge for shaping a molecular beam is described to improve the spatial separation of the species in a molecular beam by the electrostatic deflector. The spatial separation of different molecular species from each other as well as from atomic seed gas is improved. The column density of the selected molecular-beam part in the interaction zone, which corresponds to higher signal rates, was enhanced by a factor of 1.5, limited by the virtual source size of the molecular beam.Comment: 3 pages, 2 figure

Spatial separation of pyrrole and pyrrole-water clusters

We demonstrate the spatial separation of pyrrole and pyrrole(H$_2$O) clusters from the other atomic and molecular species in a supersonically-expanded beam of pyrrole and traces of water seeded in high-pressure helium gas. The experimental results are quantitatively supported by simulations. The obtained pyrrole(H$_2$O) cluster beam has a purity of ~100 %. The extracted rotational temperature of pyrrole and pyrrole(H$_2$O) from the original supersonic expansion is $T_\text{rot}=0.8\pm0.2$ K, whereas the temperature of the deflected, pure-pyrrole(H$_2$O) part of the molecular beam corresponds to $T_\text{rot}\approx0.4$ K

Dissociation dynamics of size-selected water dimer

Water is commonly said to be the matrix of life. It is built from water molecules, which are connected via hydrogen bonds. These connections have influences on many biomolecular systems and are the key to understand the importance of water on life. Somehow the smallest drop of water is the water dimer and seems to be a good candidate to study in order to understand the hydrogen bonding in water. In the framework of this thesis, the behaviour of water dimers in electric fields have been investigated. A cold and pure molecular beam containing 93(15) % of water dimers has been created by spatially separating water dimers from several different water-cluster sizes to investigate its photophysics in combination with infrared-laser radiation. Therefore, an inhomogeneous electric field was utilized, leading to a spatial shift of the water dimer and larger water clusters. A simulation of the vertical molecular beam profiles assuming the water dimer to be rigid confirmed the experimental results that the water dimer is deflecting the most, followed by the water hexamer. The initial rotational temperature of the water dimer sample could be determined to be 1.5(5) K. As the water dimer is known to be a non-rigid molecule, the Stark energies have been calculated taking intermolecular vibrations into account. First, the influence of each intermolecular motion onto the averaged electric dipole moment of the water dimer was investigated. Second, an adiabatic approximation has been used to calculate Stark energies of the non-rigid water dimer, assuming non-interacting intermolecular vibrational motions. It has been shown that the adiabatic description lead to a similar vertical molecular beam profile compared to the rigid-rotor description. The strong-field ionization of the water dimer was investigated using a high-purity molecular beam produced by an electrostatic deflector. The branching ratios of the water dimer, the anisotropy parameters and the kinetic energy releases of the water dimer fragments following single and double ionization were investigated using a velocity map imaging spectrometer. A slicing method was demonstrated to separate the fragmentation products of interest in time. Single ionization products of water dimer were dominated by a neutral dissociation involving an H$_3$O$^+$ fragment. The double ionization creates a Coulomb explosion preferentially into two H$_2$O$^+$, but also new fragmentation processes of 2OH$^+$ + 2H and H$_3$O$^+$ + O$^+$ +H were found for the first time

Pure Molecular Beam of Water Dimer

Spatial separation of water dimer from water monomer and larger water-clusters through the electric deflector is presented. A beam of water dimer with $93~\%$ purity and a rotational temperature of $1.5~$K was obtained. Following strong-field ionization using a $35~$fs laser pulse with a wavelength centered around $800~$nm and a peak intensity of $10^{14}~\text{W}/\text{cm}^2$ we observed proton transfer and $46~\%$ of the ionized water dimer broke apart into a hydronium ion $\text{H}_3\text{O}^+$ and OH

Spatial separation of 2-propanol monomer and its ionization-fragmentation pathways

The spatial separation of 2-propanol monomer from its clusters in a molecular beam by an electrostatic deflector was demonstrated. Samples of 2-propanol monomer with a purity of 90% and a beam density of $7 \times 10^6$ cm$^{-3}$ were obtained. These samples were utilized to study the femtosecond-laser-induced strong-field multi-photon ionization and fragmentation of 2-propanol using non-resonant 800 nm light with peak intensities of $3–7 \times 10^{13}$ W/cm$^2$