Rotational-state-selected Carbon Astrochemistry

The addition of individual quanta of rotational excitation to a molecule has been shown to markedly change its reactivity by significantly modifying the intermolecular interactions. So far, it has only been possible to observe these rotational effects in a very limited number of systems due to lack of rotational selectivity in chemical reaction experiments. The recent development of rotationally controlled molecular beams now makes such investigations possible for a wide range of systems. This is particularly crucial in order to understand the chemistry occurring in the interstellar medium, such as exploring the formation of carbon-based astrochemical molecules and the emergence of molecular complexity in interstellar space from the reaction of small atomic and molecular fragments

Trapping and sympathetic cooling of conformationally selected molecular ions

We report the generation, trapping and sympathetic cooling of individual conformers of molecular ions with the example of cis- and trans-meta-aminostyrene. Following conformationally selective photoionization, the incorporation of the conformers into a Coulomb crystal of laser-cooled calcium ions was confirmed by fluorescence imaging, mass spectrometry and molecular dynamics simulations. We deduce the molecules to be stable in the trap environment for more than ten minutes. The present results pave the way for the spectroscopy and controlled chemistry of distinct ionic conformers in traps

Collision-induced C_60 rovibrational relaxation probed by state-resolved nonlinear spectroscopy

Quantum state-resolved spectroscopy was recently achieved for C60 molecules when cooled by buffer gas collisions and probed with a midinfrared frequency comb. This rovibrational quantum state resolution for the largest molecule on record is facilitated by the remarkable symmetry and rigidity of C60, which also present new opportunities and challenges to explore energy transfer between quantum states in this many-atom system. Here we combine state-specific optical pumping, buffer gas collisions, and ultrasensitive intracavity nonlinear spectroscopy to initiate and probe the rotation-vibration energy transfer and relaxation. This approach provides the first detailed characterization of C60 collisional energy transfer for a variety of collision partners, and determines the rotational and vibrational inelastic collision cross sections. These results compare well with our theoretical modeling of the collisions, and establish a route towards quantum state control of a new class of unprecedentedly large molecules

Breath analysis by ultra-sensitive broadband laser spectroscopy detects SARS-CoV-2 infection

Rapid testing is essential to fighting pandemics such as COVID-19, the disease caused by the SARS-CoV-2 virus. Exhaled human breath contains multiple volatile molecules providing powerful potential for non-invasive diagnosis of diverse medical conditions. We investigated breath detection of SARS-CoV-2 infection using cavity-enhanced direct frequency comb spectroscopy (CE-DFCS), a state-of-the-art laser spectroscopic technique capable of a real-time massive collection of broadband molecular absorption features at ro-vibrational quantum state resolution and at parts-per-trillion volume detection sensitivity. Using a total of 170 individual breath samples (83 positive and 87 negative with SARS-CoV-2 based on Reverse Transcription Polymerase Chain Reaction tests), we report excellent discrimination capability for SARS-CoV-2 infection with an area under the Receiver-Operating-Characteristics curve of 0.849(4). Our results support the development of CE-DFCS as an alternative, rapid, non-invasive test for COVID-19 and highlight its remarkable potential for optical diagnoses of diverse biological conditions and disease states

A stand-alone magnetic guide for producing tuneable radical beams

Radicals are prevalent in gas-phase environments such as the atmosphere, combustion systems and the interstellar medium. To understand the properties of the processes occurring in these environments, it is helpful to study radical reaction systems in isolation—thereby avoiding competing reactions from impurities. There are very few methods for generating a pure beam of gas-phase radicals, and those that do exist involve complex set-ups. Here, we provide a straightforward and versatile solution. A magnetic radical filter (MRF), composed of four Halbach arrays and two skimming blades, can generate a beam of velocity selected low-field-seeking hydrogen atoms. As there is no line-of-sight through the device, all species that are unaffected by the magnetic fields are physically blocked; only the target radicals are successfully guided around the skimming blades. The positions of the arrays and blades can be adjusted, enabling the velocity distribution of the beam (and even the target radical species) to be modified. The MRF is employed as a stand-alone device-filtering radicals directly from the source. Our findings open up the prospect of studying a range of radical reaction systems with a high degree of control over the properties of the radical reactants

Zeeman deceleration beyond periodic phase space stability

In Zeeman deceleration, time-varying spatially-inhomogeneous magnetic fields are used to create packets of translationally cold, quantum-state-selected paramagnetic particles with a tuneable forward velocity, which are ideal for cold reaction dynamics studies. Here, the covariance matrix adaptation evolutionary strategy (CMA-ES) is adopted in order to optimise deceleration switching sequences for the operation of a Zeeman decelerator. Using the optimised sequences, a 40% increase in the number of decelerated particles is observed compared to standard sequences for the same final velocity, imposing the same experimental boundary conditions. Furthermore, we demonstrate that it is possible to remove up to 98% of the initial kinetic energy of particles in the incoming beam, compared to the removal of a maximum of 83% of kinetic energy with standard sequences. Three-dimensional particle trajectory simulations are employed to reproduce the experimental results and to investigate differences in the deceleration mechanism adopted by standard and optimised sequences. It is experimentally verified that the optimal solution uncovered by the evolutionary algorithm is not merely a local optimisation of the experimental parameters { it is a novel mode of operation that goes beyond the standard periodic phase stability approach typically adopted

Cold state-selected radicals for the study of low temperature chemistry

Generating a controllable and pure source of molecular free-radicals or open-shell atoms has been one of the primary barriers hindering the detailed study of radical processes in the laboratory. In this thesis, a novel source of state-selected radicals -- composed of a Zeeman decelerator interfaced with a newly-designed magnetic guide -- is introduced. This tuneable source generates a pure beam of velocity-selected hydrogen atoms that will enable the study of radical interactions with exceptional control over the properties of the radical species. In Zeeman deceleration, time-varying spatially inhomogeneous magnetic fields are used to create packets of translationally cold, quantum-state-selected paramagnetic particles with a tuneable forward velocity, which are ideal for cold reaction dynamics studies. In a proof-of-principle experiment, the Zeeman deceleration of nitrogen atoms in the metastable 2D5/2 state from 460 to 410 m/s is demonstrated for the first time. The covariance matrix adaptation evolutionary strategy (CMA-ES) is adopted in order to optimise deceleration switching sequences for the operation of a 12-stage Zeeman decelerator. Using the optimised sequences, a 40% increase in the number of decelerated H(2S1/2) atoms is observed compared to standard sequences for the same final velocity, imposing the same experimental boundary conditions. Furthermore, up to 98% of the initial kinetic energy of particles in the incoming beam is removed by the optimised sequences, compared to the removal of a maximum of 83% of kinetic energy with standard sequences. Three-dimensional particle-trajectory simulations show that the optimal solution uncovered by the evolutionary algorithm is not merely a local optimisation of the experimental parameters -- it is a new mode of operation that goes beyond the standard periodic phase stability approach typically adopted. A novel magnetic guide is designed and constructed to purify the post-deceleration beam. Only radicals with a selected velocity are transmitted through the guide; all other components of the incoming beam (radical species travelling at other velocities, precursor molecules and seed gases) are removed. The guide is composed of four Halbach arrays -- hexapolar focusing elements -- and two skimming blades. The relative positions of these components can be adjusted to tune the properties of the resulting beam and to optimise transmission for a given velocity. Experimental measurements of Zeeman-decelerated H atoms transmitted through the guide, combined with extensive simulations, show that the magnetic guide successfully removes 99% of H atoms travelling outside the narrow target velocity range.</p

Manipulating hydrogen atoms using permanent magnets: Characterisation of a velocity-filtering guide dataset

Raw data, simulations and analysis code for the evidence presented in the paper "Manipulating hydrogen atoms using permanent magnets: Characterisation of a velocity-filtering guide" by Jutta Toscano, Michal Hejduk, Henry G. McGhee and Brianna R. Heazlewood published in Rev. Sci. Instrum. (2019). See DESCRIPTION.txt file within

Cold state-selected radicals for the study of low temperature chemistry

Generating a controllable and pure source of molecular free-radicals or open-shell atoms has been one of the primary barriers hindering the detailed study of radical processes in the laboratory. In this thesis, a novel source of state-selected radicals -- composed of a Zeeman decelerator interfaced with a newly-designed magnetic guide -- is introduced. This tuneable source generates a pure beam of velocity-selected hydrogen atoms that will enable the study of radical interactions with exceptional control over the properties of the radical species. In Zeeman deceleration, time-varying spatially inhomogeneous magnetic fields are used to create packets of translationally cold, quantum-state-selected paramagnetic particles with a tuneable forward velocity, which are ideal for cold reaction dynamics studies. In a proof-of-principle experiment, the Zeeman deceleration of nitrogen atoms in the metastable 2D5/2 state from 460 to 410 m/s is demonstrated for the first time. The covariance matrix adaptation evolutionary strategy (CMA-ES) is adopted in order to optimise deceleration switching sequences for the operation of a 12-stage Zeeman decelerator. Using the optimised sequences, a 40% increase in the number of decelerated H(2S1/2) atoms is observed compared to standard sequences for the same final velocity, imposing the same experimental boundary conditions. Furthermore, up to 98% of the initial kinetic energy of particles in the incoming beam is removed by the optimised sequences, compared to the removal of a maximum of 83% of kinetic energy with standard sequences. Three-dimensional particle-trajectory simulations show that the optimal solution uncovered by the evolutionary algorithm is not merely a local optimisation of the experimental parameters -- it is a new mode of operation that goes beyond the standard periodic phase stability approach typically adopted. A novel magnetic guide is designed and constructed to purify the post-deceleration beam. Only radicals with a selected velocity are transmitted through the guide; all other components of the incoming beam (radical species travelling at other velocities, precursor molecules and seed gases) are removed. The guide is composed of four Halbach arrays -- hexapolar focusing elements -- and two skimming blades. The relative positions of these components can be adjusted to tune the properties of the resulting beam and to optimise transmission for a given velocity. Experimental measurements of Zeeman-decelerated H atoms transmitted through the guide, combined with extensive simulations, show that the magnetic guide successfully removes 99% of H atoms travelling outside the narrow target velocity range.</p

Zeeman deceleration beyond periodic phase space stability

Raw data, simulations and analysis code for the evidence presented in the paper "Zeeman deceleration beyond periodic phase space stability" by Jutta Toscano, Atreju Tauschinsky, Katrin Dulitz, Christopher J. Rennick, Brianna R. Heazlewood and Timothy P. Softley published in New J. Phys. 19 (2017) 083016