Research Projects

Chemical phenomena in condensed molecular solids have implications to chemistry, physics, biology, and industry. These molecular solids are present in the universe and processes on them have relevance to interstellar chemistry and atmospheric processes of several planets. Water-ice is one of the most abundant condensed phase species in the universe. Clathrate hydrates (CHs) are one of the forms of molecular solids, which are crystalline inclusion compounds in which guest molecules are included in hydrogen-bonded water-cages. CHs are generally formed at high pressures and at ambient temperatures under the earth or on the ocean floor. We have shown the formation of CHs under ultra-high vacuum (UHV) and at cryogenic conditions of relevance to space. We observed that co-deposition of CH₄ and H₂O in UHV results in the formation of CH₄ hydrate at 30 K, upon prolonged annealing. CO₂ is also capable of forming CH at 10 K and 10-¹⁰ mbar. This proposal is motivated by a desire to gain more insights into the chemical transformations of CHs, catalysis reactions between metal species and CHs formed under UHV environment and possible implications of such science to the chemical evolution of the universe. A systematic study of these elementary processes which have relevance to interstellar chemistry requires the right choice of experimental tools. We have been using reflection absorption infrared spectroscopy (RAIRS) and temperature programmed desorption-mass spectrometry (TPD-MS), for which we have developed considerable expertise with the support of DST. In our state-of-art instrument, developed using a previous grant, we can perform these studies at a base vacuum of 5×10-¹⁰ mbar, starting from 7 K. With a hydrogen continuum incorporated to the chamber, it will be possible to study photochemistry on CHs and their modified forms. We will deposit metal vapours onto preformed CH surfaces by using the existing metal evaporator. Metals can initiate heterogeneous catalysis and photo-catalysis with CHs, which may lead to new products. We would like to explore the possibility of forming mixed CHs, where two different guest molecules would encase in separate cages. Further, these mixed CHs could be subjected to metal exposure and subsequent studies on catalysis and photo-catalysis will be performed. Besides TPD-MS and RAIRS, we will use low energy ion scattering and secondary ion mass spectrometry. Systems chosen for these investigations will be selected based on their relevance to space. From all these proposed studies, we hope to discover new reactions and related novel phenomena under ultra-cold conditions. The existing instrument will be modified to install a vacuum ultra-violet (VUV) light source in the initial part of the project and the integrated system will be characterized for its performance.