In a breakthrough experiment using a novel negative ion momentum imaging technique, researchers from Tata Institute of Fundamental Research, Mumbai India and Open University, Milton Keynes, UK have shown – for the first time that incoherent electrons displaying their quantum mechanical nature, can induce coherence in molecular systems on attachment.
In other words, this coherence induced in the molecule segregates the charge and excess energy in the system in a preferred manner. Similar measurements in the Isotopomer of H2 namely D2 does not show such a strong asymmetry in ejection of the fragment ion but shows the reversal of the asymmetry as a function of incoming electron energy.
The coherence in the resulting excited molecular entity is understood to stem from the absorbed laser radiation. By demonstrating the presence of such coherence resulting from a capture of an incoherent electron, Prof. Krishna Kumar and co-workers have shown that such coherence can also stem from the transfer of more than one value of angular momentum quanta.
This is known as dissociative attachment. According to Prof. Krishna Kumar, dissociative attachment is traditionally linked with transfer of multiple values of angular momentum quanta in the molecular system. However, it is for the first time such a quantum coherent response has been observed from a molecule.
Krishna Kumar and Dr. Prabhudesai in TIFR has pioneered research on several aspects of low energy electron interactions with molecules in gas and condensed phase with particular emphasis on the possibility of controlling chemical reactions using low energy electrons. They also pose a challenge to theoreticians to come up with a detailed model for the negative ion chemistry that is associated with low energy free electron scattering.
Low energy electrons are ubiquitous and are known to play important role in variety of phenomena relevant to iatrochemistry, in radiation biology, atmospheric chemistry, radioactive waste management and nanolithography – to name but a few. In all these cases, dissociative attachment plays a critical role.
These measurements were carried out by Prof. Krishna Kumar using an experiment built by him at the Open University in UK, where he was on invitation as a Marie Curie Professor to help build a novel electron scattering experiment for the European scientists, similar to the one he had conceived and built at TIFR.