Probing Molecular Solids with Low-Energy Ions

Abstract

Ion/surface collisions in the ultralow-to low-energy (1-100-eV) window represent an excellent technique for investigation of the properties of condensed molecular solids at low temperatures. For example, this technique has revealed the unique physical and chemical processes that occur on the surface of ice, versus the liquid and vapor phases of water. Such instrumentdependent research, which is usually performed with spectroscopy and mass spectrometry, has led to new directions in studies of molecular materials. In this review, we discuss some interesting results and highlight recent developments in the area. We hope that access to the study of molecular solids with extreme surface specificity, as described here, will encourage investigators to explore new areas of research, some of which are outlined in this review.

Proton Transport and Related Chemical Processes of Ice

“…Excellent reviews have been published on the chemical processes of ice surfaces. These reviews are primarily focused on the structure of ice surfaces and adsorbate–surface interactions; surface chemical properties of frozen water films and sulfuric acid films; adsorption and ionization of hydrogen chloride on ice surfaces; elementary steps of reactions on ice surfaces; theoretical studies on heterogeneous reactions related to atmospheric ozone depletion; structure, molecular diffusivity, and reactions on ice surfaces; reactive scattering processes of low-energy ion beams on ice surfaces; , and adsorption, diffusion, and reactions on amorphous solid water (ASW) films relevant to cosmic dust grains. , The previous studies have mainly investigated the processes that occur on the surface of ice partly because chemical reactions occur more easily on the surface, where the molecular diffusivity is higher than that in the interior of ice. Additionally, various surface spectroscopic techniques are available for the analysis of the chemical states of ice surfaces in ultrahigh-vacuum (UHV) environments.…”

Interaction of Acetonitrile with Alcohols at Cryogenic Temperatures

“…A systematic understanding of physical and chemical changes of molecular solids is a subject of intense study from several perspectives. It ranges from acquiring a fundamental knowledge on such systems to their relevance in space science. − In laboratory conditions, thin films of molecular solids having less ordered structure (also known as amorphous solids) are grown by vapor deposition at low temperature and pressure, which upon annealing to higher temperature undergo phase transition to their respective crystalline phases . Phase transition is one of the important physical changes that can drastically alter the face and fate of molecular solids.…”

Diffusion and Crystallization of Dichloromethane within the Pores of Amorphous Solid Water

“…Different phases of molecular solids provide unique physical and chemical environment. This is a vast area of research, and phase transition of different molecules has been investigated in great detail. − Techniques used for this study are mostly spectroscopic and scattering methods, namely, X-ray diffraction, low-energy electron diffraction (LEED), electron diffraction, transmission electron microscopy (TEM), low-energy ion collisions, ,, and most commonly by infrared (IR) spectroscopy. ,, The last one in this list has been utilized to study phase transitions in water-ice, , methanol-ice, and many other molecular solids. ,− Although dichloromethane is one of the most frequently used organic solvents in the laboratory, the phase transition of this molecule is not well-understood. In 1970, the crystal structure of dichloromethane has been predicted from an IR spectroscopic study .…”