Final Report Summary - MIND (Investigation of electron induced chemical control using momentum imaging of negative ions from dissociative electron attachment) The project was aimed at establishing a new experimental facility in Europe to study the dynamics of the dissociative electron attachment (DEA) process in gas and condensed phases. This was to be followed by modifying the existing gas phase experimental facility as well as creating a new condensed phase facility at TIFR in India in the return phase for studying low energy electron-molecule interactions.DEA is now understood to be the most crucial process in the long chain of events that lead to chemical change in any medium subjected to energetic radiation and inside processing plasmas. The DEA process allows very efficient coupling of kinetic energy into potential energy of the system by creating radicals, negative ions and excited molecules, all which are chemically very active. The chemical changes that are enhanced or even initiated by the DEA are important to atmospheric chemistry, astrochemistry, plasma physics and chemistry, nanolithography, dielectric aging, radiation waste management, pollution control, photochemistry at surfaces and radiation damage and therapy. In this context, it is important to understand the DEA process in various molecules in gas phase as well in condensed phase. In DEA, a low energy electron interacts with a molecule and gets resonantly attached to it forming a transient negative ion. Depending on the life time of this resonance and the nature of its potential energy surface, the transient ion decays by ejection of the electron or through dissociation into one or more neutral fragments and a negative ion fragment. The observables in the DEA process are the electron energies at which the molecule captures the electron, the shape and spread of this energy dependence, the types of negative ion fragments that are produced, the absolute cross sections for their formation as a function of the electron energy, and the kinetic energy and angular distribution of the fragment negative ions. While all these parameters are important in characterising the DEA process and their knowledge is important to various practical applications, the structure of the transient negative ion and the dynamics of its formation and decay are essentially ingrained in the kinetic energy and angular distribution of the fragment ions. These parameters also provide critical information on the composition and internal energy of the neutral radicals formed by DEA, which are very difficult to be studied directly.The IIF had developed at TIFR a very novel and highly efficient technique for momentum imaging of fragment negative ions formed in low energy electron-molecule collisions. This setup had the additional feature of imaging in full 360o angular range with respect to the electron beam, which enabled the observation of negative ions being ejected in the 0o and 180o directions (the two directions most crucial in testing a theoretical model) for the first time. The tenure as IIF at the Open University in Milton Keynes, UK, provided an opportunity for further development of this technique, resulting in better features like increased sensitivity, higher mass resolution and ease of operation. Using the expertise available at the Open University and other European labs, a second experiment for momentum imaging the negative ions formed out of electron collision on molecules in condensed phase was designed. The stay in Europe resulting in increased interaction with the European researchers provided the IIF several new insights as well expertise in condensed phase studies. Summary of activities during the return phase:- Setting up a new experiment for condensed phase measurements: During the return phase, the IIF has used the expertise that he gained in condensed phase studies to set up a new experiment at TIFR to carry out electron-molecule collisions in the condensed phase. The group led by the IIF at TIFR had discovered the functional group dependence in DEA and its role in chemical control using electrons, by a series of measurements in gas phase. It was felt necessary that this should be investigated in the condensed phase. For this, an experiment has been built to bombard molecules deposited on a clean metal substrate held at 20 K by low energy electrons of specific know energies. The chemical transformation of the molecules arising from the electron collision would be analysed using a Fourier transform infra-red spectrometer. A new graduate student and two postdoctoral workers have been working on this experiment under the guidance of the IIF starting from the design, construction of the apparatus and measurements. Both these postdoctoral workers had been trained in European labs, one on theoretical aspects of electron controlled chemistry (Dr Daly Davis from University of Heidelberg) and the other one on condensed phase studies (Dr Bhalamurugan Sivaraman from the Open University, UK).- Proposals for new experiments to be carried out at TIFR: Along with other colleagues at TIFR two new funding proposals have been initiated during this period. The first one is for carrying out DEA studies on radicals and molecules in selected excited states. The second one is for studying the DEA for single molecules on surfaces using an STM. - Continuination of the gas phase studies using the existing experiment: The momentum imaging experiment in the gas phase is being continued and a new graduate student is working on it under the guidance of the IIF. A new experiment for the gas phase experiments are being designed taking into account several new insights gained by building the experiment at the Open University. - Analysis of data and preparation of manuscripts based on the work done in Europe: Several important experiments on DEA to various molecules were conducted during the stay as an IIF. These include the momentum imaging of O- from CO, H- from H2, D- from D2, absolute cross sections for H- from H2 and D- from D2 and momentum imaging of various negative ions from CF4 and its halogen derivatives. Two sets of data were analysed and manuscripts completed during the return phase in collaboration with various European colleagues. - Guiding three European students for their PhD work: During the stay at the OU as an IIF, three students were associated with the IIF. One of them from Iceland completed his Masters and is continuing for his PhD work. The IIF is also guiding a PhD student on DEA studies using the momentum imaging spectrometer at the OU by interacting with her on a weekly basis through the internet. The IIF is also the external supervisor for another student at the OU, who works on astrochemical ices.- Visits to Europe to continue the collaboration and attend conferences: During the return phase, the IIF visited the Open University twice for discussions, continued interaction with the students and the development of the condensed phase momentum imaging experiment that had been designed during the earlier tenure. These visits were also timed to participate in the international organisation committee meeting of ICPEAC as well as to attend the meeting itself and also its satellite meeting dealing with electron and positron collisions on molecules. - Initiating theoretical studies on DEA process at TIFR by having experts from Europe visit TIFR: The gas phase momentum data obtained using the new experiments at the OU and TIFR need theoretical support for better understanding of the DEA process. There are very few groups in the world who are competent in carrying out the complex calculations on DEA. TIFR had initiated collaboration with the theoretical chemistry group in University of Bonn. This has been continuing. In order to strengthen this collaboration further and enhance the theoretical support by training more people in the complex calculations, a long term visit of Dr Bernd Nestmann from University of Bonn to TIFR was arranged. He spent three months at TIFR in training younger colleagues and making new calculations for understanding some of the data that were obtained using the experiment at the Open University.- Talks at various places, including conferences: Talks at three conferences held in India, visits to two different organisations - BARC Mumbai and IIT Chennai highlighting the DEA process and the new results.
