The Chemistry of Cold Interstellar Cloud Cores Gas-Phase Reactive Collisions at Very Low Temperatures: Recent Experimental Advances and Perspectives The Study of Cold Collisions Using Ion Guides and Traps Theory of Low-Temperature Gas-Phase Reactions Molecular Spectroscopy at Low Temperatures: A High-Resolution Infrared Perspective The Production and Study of Ultra-Cold Molecular Ions Chemical Dynamics: Inside Superfluid Helium Nanodroplets at 0.37 K Kinematic Cooling of Molecules Manipulation of Molecules with Electric Fields Cold Collisions, Quantum Degenerate Gases, Photoassociation, and Cold Molecules.
The Chemistry of Cold Interstellar Cloud Cores Gas-Phase Reactive Collisions at Very Low Temperatures: Recent Experimental Advances and Perspectives The Study of Cold Collisions Using Ion Guides and Traps Theory of Low-Temperature Gas-Phase Reactions Molecular Spectroscopy at Low Temperatures: A High-Resolution Infrared Perspective The Production and Study of Ultra-Cold Molecular Ions Chemical Dynamics: Inside Superfluid Helium Nanodroplets at 0.37 K Kinematic Cooling of Molecules Manipulation of Molecules with Electric Fields Cold Collisions, Quantum Degenerate Gases, Photoassociation, and Cold Molecules.
Studying chemical reactions at very low temperatures is of importance for the understanding of fundamental physical and chemical processes. At very low energies, collisions are dominated by only a few partial waves. Thus, studies in this regime allow the characterisation of quantum effects which depend on the collisional angular momentum, e.g., reactive scattering resonances and tunneling through centrifugal barriers. Additionally, the dynamics of ultralow-energy collisions is dominated by long-range interactions, i.e., "universal" chemical forces. Thus, experiments in this domain probe the details of intermolecular interactions which is of general relevance for the understanding of chemical processes. Moreover, the increasingly more precise experiments provide valuable data for benchmarking theoretical models and quantum-chemical calculations. Studies of cold ion-neutral reactions in the laboratory rely on techniques for the generation of cold ions and cold neutrals. Many of these techniques do not only allow the translational cooling of the molecules, but also a precise reparation of their internal quantum state. Thus, by an accurate preparation of both the energy and state of the reaction partners as well as by the application of external electric, magnetic or optical fields, prospects open up to study and control chemical processes at an unprecedented level of accuracy. In this chapter, we will review salient theoretical concepts and recent experimental developments for studies of ion-molecule reactions at low temperatures. We first discuss the theoretical background for the description of low-energy ion-molecule reactions. Next we present key experimental methods for laboratory studies of cold ion-molecule reactions. The chapter concludes with a review of illustrative results and an outlook on future directions.
Collisions of molecules in a thermal gas are difficult to control. Thermal motion randomizes molecular encounters and diminishes the effects of external radiation or static electromagnetic fields on intermolecular interactions. The effects of the thermal motion can be reduced by cooling molecular gases to low temperatures. At temperatures near or below 1 K, the collision energy of molecules becomes less significant than perturbations due to external fields. At the same time, inelastic scattering and chemical reactions may be very efficient in low-temperature molecular gases. The purpose of this article is to demonstrate that collisions of molecules at temperatures below 1 K can be manipulated by external electromagnetic fields and to discuss possible applications of cold controlled chemistry. The discussion focuses on molecular interactions at cold (0.001-2 K) and ultracold (<0.001 K) temperatures and is based on both recent theoretical and experimental work. The article concludes with a summary of current challenges for theory and experiment in the research of cold molecules and cold chemistry.
One of the current themes in quantum physics is the creation of cold ( 1 K) molecules to study molecule-molecule, molecule-atom, and molecule-radiation interactions under these novel low-temperature conditions. This book highlights the field of cold trapped molecular ions. In particular, the development of a novel, universal cooling method for charged particles, sympathetic cooling using laser-cooled atoms, together with the experimental and computational techniques required are extensively reviewed. The book also reviews first spectacular applications of the cold ion ensembles produced: the study of the properties of cold non-neutral plasmas, the study of ion-neutral chemical reactions and of photodissociation processes, and high-resolution rotational overtone spectroscopy of cold hydrogen molecular ions with unprecedented spectral resolution. The large potential of this field of research and its possible impact to other fields of physics, chemistry, and biology are highlighted. The book summarizes the main lines of research in cold trapped molecular ion physics, thus, making it useful as an introduction for advanced students and experienced researchers.
Studying chemical reactions at very low temperatures is of importance for the understanding of fundamental physical and chemical processes. At very low energies, collisions are dominated by only a few partial waves. Thus, studies in this regime allow the characterization of quantum effects which depend on the collisional angular momentum, e.g., reactive scattering resonances and tunneling through centrifugal barriers. Additionally, the dynamics of ultralow-energy collisions is dominated by long-range interactions, i.e., “universal” chemical forces. Thus, experiments in this domain probe the details of intermolecular interactions which is of general relevance for the understanding of chemical processes. Moreover, the increasingly more precise experiments provide valuable data for benchmarking theoretical models and quantum chemical calculations. Studies of cold ion–neutral reactions in the laboratory rely on techniques for the generation of cold ions and cold neutrals. Over the last decades, the technology in this domain has made impressive progress. Many of these techniques allow not only the translational cooling of the molecules, but also a precise preparation of their internal quantum state. Thus, by an accurate preparation of both the energy and state of the reaction partners as well as by the application of external electric, magnetic or optical fields, prospects open up to study and control chemical processes at an unprecedented level of accuracy. In this chapter, we review salient theoretical concepts and recent experimental developments for studies of ion–molecule reactions at low temperatures. We first discuss the theoretical background for the description of low-energy ion–molecule reactions. Next we present key experimental methods for laboratory studies of cold ion–molecule reactions. The chapter concludes with a review of illustrative results and an outlook on future directions.
Collisions of molecules in a thermal gas are difficult to control. Thermal motion randomizes molecular encounters and diminishes the effects of external radiation or static electromagnetic fields on intermolecular interactions. The effects of the thermal motion can be reduced by cooling molecular gases to low temperatures. At temperatures near or below 1 K, the collision energy of molecules becomes less significant than perturbations due to external fields. At the same time, inelastic scattering and chemical reactions may be very efficient in low-temperature molecular gases. The purpose of this article is to demonstrate that collisions of molecules at temperatures below 1 K can be manipulated by external electromagnetic fields and to discuss possible applications of cold controlled chemistry. The discussion focuses on molecular interactions at cold (0.001-2 K) and ultracold (<0.001 K) temperatures and is based on both recent theoretical and experimental work. The article concludes with a summary of current challenges for theory and experiment in the research of cold molecules and cold chemistry.
The recent development of a range of techniques for producing cold atoms and molecules at very low translational temperatures T < or = 1 K has provided the opportunity to investigate collisional processes in a new physical regime. We have recently presented a new experimental method to study low-temperature reactive collisions between translationally cold ions and neutral molecules (S. Willitsch et al., Phys. Rev. Lett. 2008, 100, 043203). Our technique relies on the combination of a quadrupole-guide velocity selector for the generation of translationally cold neutral molecules with a facility to produce ordered structures of cold ions (Coulomb crystals) by laser cooling in a linear quadrupole ion trap. The strong localisation of the ions in the trap in combination with the high sensitivity of laser-induced-fluorescence detection enabled us to study chemical reactions on the single-particle level, down to temperatures of T approximately 1 K. In the current paper, we present a detailed characterisation of the scope and limitations of this method based on our study of the reaction between laser-cooled Ca+ ions and velocity-selected CH3F molecules. The properties of our cold-neutrals source and the dependence of the measured rate constant on the shape of the Coulomb crystals, trapping and laser-cooling parameters are discussed. An extension of our technique for the study of low-temperature reactions with sympathetically cooled molecular ions (translational temperature T > 10 mK) is presented and first results on the charge-transfer reaction between OCS+ and ND3 are discussed. Finally, perspectives for further developments of our method are explored.