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The resonant low-energy electron (LEE) induced scattering off biomolecules is proposed to undergo dissociative electron attachment (DEA) as one of the favoured pathways. In the current work, we have considered the citric acid molecule due to its biological relevance in the Krebs cycle, in which LEEs may affect and lead to metabolic dysfunction. To investigate the DEA pathway of citric acid, we implemented the local complex potential-based time-dependent wavepacket (LCP-TDWP) approach. From our calculation, we observed that the vertical attachment energy (VAE) of the citric acid system is found to be −1.17 eV, and the electron attaches itself to the 2-carboxylic acid group to form a transient negative ion (TNI) which further dissociates into a free radical and a radical anion. The lifetime for the TNI is around 1000 fs, with a maximum cross-section seen at 1.09 eV. The interaction of low-energy electrons with citric acid can lead to dissociative electron attachment (DEA). In the current work, we used the local complex potential-based time-dependent wave packet (LCP-TDWP) approach to investigate DEA to citric acid. The time evolution of the probability density suggests the possibility of a boomerang model. [ABSTRACT FROM AUTHOR]

Surface-enhanced Raman spectroscopy (SERS), a very powerful tool for the identification of molecular species, has relied mostly on noble metal-based substrates to obtain a high enhancement factor. In this work, we demonstrate that self-driven intrinsic defects in 2D palladium di-selenide (PdSe2) dendrites grown at low temperature (280 °C) act as hotspots for high SERS enhancement. We grow 2D dendritic PdSe2 with ample intrinsic defects to exploit it for SERS application. X-ray electron spectroscopy (XPS) analysis reveals 9.3% outer layer and 4.7% interior Se vacancies. A detailed examination of atomic-scale defects revealed Se vacancy (VSe) coupled with Se–Pd–Se vacancy (VSe-Pd-Se) in monolayer PdSe2, and an array of line defects (Se vacancies) and nanopores in bilayer PdSe2 dendrites. Interestingly, our studies reveal that Se vacancy-rich PdSe2 gives rise to line defects that act like hotspots for SERS enhancement. Remarkably, the vacancy-rich dendritic PdSe2 shows a SERS enhancement factor >105 and can detect RhB at a concentration down to 10−8 M. We speculate that the topological line defects and the edge construction in PdSe2 dendrites act as metallic wire or edge, which is partly responsible for the high enhancement in the SERS signal. The high SERS sensitivity is explained on the basis of multiple charge transfer processes combined with the predicted metal-like behavior of the defected 2D PdSe2. Our conclusions are fully supported by the density functional theory calculation of the electronic density of states of the defective bilayer (2L) PdSe2, which remarkably exhibits metallic character. Being a defect-enabled SERS substrate, dendritic 2D PdSe2 fills the gap between conventional plasmonic SERS substrate and plasmon-free SERS substrate. [ABSTRACT FROM AUTHOR]

Vibrational excitation cross-sections $\sigma_{\nu_f \leftarrow \nu_i } (E)$ in resonant e-F and HCl scattering are calculated from transition matrix elements $T_{\nu_f \leftarrow \nu_i } (E)$ obtained using Fourier transform of the cross correlation function $\left\langle {\phi_{\nu_f } \left( R \right)\vert \Psi_{\nu_i } \left( {R,t} \right)} \right\rangle $ where $\Psi_{\nu_i } \left( {R,t} \right)\approx e^{-i\hbar H_{AB^-} \left( R \right)t}\phi_{\nu { }_i} \left( R \right)$. Time evolution under the influence of the resonance anionic Hamiltonian H- (AB=F/HCl) is effected using Lanczos reduction technique followed by fast Fourier transform and the target (AB) vibrational eigenfunctions $\phi _{\nu_i } \left( R \right)$ and $\phi_{\nu_f } \left( R \right)$ are calculated using Fourier grid Hamiltonian method applied to potential energy (PE) curve of the neutral target. The resulting vibrational excitation cross-sections provide reasonable agreement with experimental and other theoretical results. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Results from application of a new implementation of the time-dependent wave packet (TDWP) approach to the calculation of vibrational excitation cross-sections in resonant e-CO scattering are presented to examine its applicability in the treatment of e-molecule resonances. The results show that the SCF level local complex potential (LCP) in conjunction with the TDWP approach can reproduce experimental features quite satisfactorily. [ABSTRACT FROM AUTHOR]

Selective control of HOD photodissociation (H--O + D ← HOD → H + O--D) has been theoretically investigated using CW lasers with appropriate carrier frequency and |0, 0>, |0, 1> and |0, 2> with zero quantum of excitation in the O-H bond and zero, one and two quanta of excitation in the O--D bond as the initial states. Results indicate that the O--H bond in HOD can be selectively dissociated with a maximum flux of 87% in the H + O--D channel from the ground vibrational state |0, 0>. For the O--D bond dissociation, it requires two quanta of excitation (|0, 2>) in the O--D mode to obtain 83% flux in the H--O + D channel. Use of a two colour laser set-up in conjunction with the field optimized initial state (FOIST) scheme to obtain an optimal linear combination of |0, 0> and |0, 1> vibrational states as the initial state provides an additional 7% improvement to flux in the H--O + D channel as compared to that from the pure |0, 1> state. [ABSTRACT FROM AUTHOR]