Measuring cold and controlled chemical processes and vibrational spectroscopy

This thesis delves into the properties of ions, and describes and demonstrates methods of probing ionic properties and reactivity using cold and controlled techniques. This in turn, enables better understanding of how ions are formed in astrochemical environments and how they react with polar neutral molecules. Ionic properties are probed within a linear Paul ion trap system (for ion--molecule reactions and ion trajectory investigations), as well as a 22-pole cryogenic ion trap (for vibrational spectroscopy). This thesis focuses on two ion--molecule reaction systems: reactions of room temperature water isotopologies (H₂O and D₂O) with sympathetically cooled Kr⁺ ions and reactions of rotationally cooled ammonia (NH₃ and ND₃) isotopologues with sympathetically cooled Ar⁺ ions. Experimental ion--molecule reaction rate coefficients are compared with a variety of capture theories and ab initio calculations, and with prior experimental measurements. A comprehensive review of capture theories is provided, to more generally address the suitability of capture theories in the context of ion--molecule reactions below 300 K, and for use in astrochemical models. The reactions of water isotopologues are found to be in excellent agreement with classical capture theories, with no isotope effects observed. Ongoing work seeks to ascertain the reactivity of rotationally cold ammonia with Ar⁺. Preliminary data is discussed, indicating an enhancement of rate coefficients with rotationally cold ammonia and increased inverse kinetic isotope effect compared to the reactions of room temperature ammonia. To aid our understanding of ion--molecule reactions and to probe ion behaviour, a novel approach is presented. The spatial and temporal distibution of ejected ions from Coulomb crystals is measured, using a Timepix3 camera coupled with a microchannel plate detector and phosphor screen. Here, the positions of non-fluorescent ions within Coulomb crystals can be directly experimentally measured, for the first time. Results \correction{indicate} that, with the apparatus used in this work, there is a mass-to-charge dependence on where ions hit the detector. To further explore ionic behaviour, the fragmentation of thiophene ions is probed through vibrational spectroscopy. The mass-to-charge, m/z, 58 fragment, is investigated under cold conditions. Results are analysed using potential energy surfaces, mass-analysed ion kinetic energy spectroscopy, and theoretical vibrational spectra. It is conclusively shown that the m/z 58 fragment is the H2CCS⁺ ion, demonstrating a novel method for generation of this isomer selectively.