Research Projects

Roaming reactions are a novel class of reaction pathways characterized by non-intuitive, loose transition states which occur through frustrated bond cleavage on shallow potential energy surfaces. First evidenced in formaldehyde photodissociation, the roaming mechanism has since been observed in a wide range of systems with varieties of roaming fragments like NO₂, CO, HCO, and CH₃ radicals. Apart from small molecular systems, roaming has also been observed in intramolecular Coulombic decay processes of molecular clusters, such as 2,6-difluorophenylacetylene-trimethylamine and 2,6-difluorophenylacetylene-dimethylamine clusters. Based on these reports, it is observed that with advances in spectroscopic techniques and theoretical calculations, the roaming mechanism has emerged as a widely prevalent pathway in molecular systems. The evidence for roaming-mediated photodissociation in formaldehyde, acetaldehyde, and acetone has been revealed from the measurement of the translational energy distribution profiles of CO and HCO radicals, produced from the T₁ and S₀ states. In general, aldehydes and ketones, as well as nitro compounds, both aliphatic and aromatic, exhibit NO2 roaming along the NO release pathway, where intramolecular hydrogen bonding stabilizes the roaming transition state. It has been demonstrated that in the case of o-nitroaniline, the NH2 moiety in ortho position to the NO2 group stabilizes the roaming transition state through intramolecular hydrogen bonding, promoting the NO2 roaming along the NO loss channel. Based on these observations, it can be proposed that NH2 substituted in carbonyl compounds, amides, can also show roaming-mediated dissociation. To verify this conjecture, this project aims to investigate the photodissociation dynamics of aliphatic and aromatic amides including formamide, acetamide, acrylamide, methacrylamide, benzamide, and substituted 2-pyrrolidinone, with a focus on CO, HCO, and NH loss channels. Velocity Map Imaging (VMI) will be used to simultaneously capture the velocity and angular distributions of photoproducts, providing detailed insight into the energy and state-specific dynamics. Given that amides absorb weakly beyond 250 nm, dissociation will be studied in the 213–230 nm range using Resonance Enhanced Multiphoton Ionization (REMPI) and universal ionization techniques. Complementary theoretical studies, including PES mapping and ab initio molecular dynamics, will be carried out to interpret experimental results and characterize roaming transition states. Beyond mechanistic interest, this work has broader implications due to its biogenic, atmospheric relevance. Amides are biologically relevant as peptide bond formers and are considered prebiotic molecules. Their photodissociation products (CO, HCO, and NH) are also precursors to complex molecules in comets and meteorites. Thus, this study will contribute to our understanding of amide reactivity in both biological and Interstellar medium.