arXiv subjects

Sumit Srivastav

Publications and source records attributed to Sumit Srivastav.

4 recordsLinked to original sources

arXiv2026

Direct evidence for projectile electronic structure effects in slow multielectron capture collisions

We investigate the role of the electronic structure of the projectile in ionization and subsequent fragmentation of CO$_2$ induced by multielectron capture in collisions at 0.31 a.u. impact velocity. Focusing on the $\text{CO}_2^{3+} \rightarrow \text{O}^+:\text{C}^+:\text{O}^+$ break-up channel as a representative channel, we report kinetic energy release distributions (KERDs) for collisions with equi-velocity N$^{q+}$ and O$^{q+}$ projectiles. We consider two complementary categories of measurements. In the first category, in which different projectiles of the same charge are considered, we find that KERDs obtained with N$^{q+}$ and O$^{q+}$ impact ($q=4,6$) are broadly similar, but they differ significantly from the earlier reported KERD with Ar$^{q+}$ impact. In the second category, pronounced differences are observed between the KERDs obtained with isoelectronic N$^{q+}$ and O$^{(q+1)+}$ ($q=3,5,7$) projectiles. These results provide direct evidence that projectile electronic structure plays a critical role in multielectron capture collisions.

physics.atom-ph↗

arXiv2026

Association between projectile and target excitation in slow Ar$^{q+}$-CO$_2$ collisions

We investigate ionic fragmentation of CO$_2^{n+}$~\mbox{($2\le n\le 4$)} produced in collisions with Ar$^{q+}$~\mbox{($4\le q\le 16$)} projectiles at a collision velocity of $\approx$~0.3~a.u. For most projectile and fragmentation channel combinations, the shape of the kinetic energy release distribution (KERD) differs with the electron capture mediated charge change (\mbox{$\Delta q$}) in the scattered projectile: KERD for \mbox{$\Delta q = 2$} is broader at high KER than for \mbox{$\Delta q =1$}. The difference generally diminishes with increasing projectile charge. Two deviations in this general trend are seen in the fragmentation of CO$_2^{3+}$, one for Ar$^{4+}$ impact in the high KER region and the other for Ar$^{6+}$ impact in the low KER region. The calculated reaction windows for multielectron capture within the framework of the extended classical over-the-barrier model (ECOBM) indicate that while ionization of the target occurs via multielectron capture, the scattered projectile may subsequently undergo multi-fold autoionization. Interpreting projectile autoionization to be a consequence of capture into highly excited states and high fragment KER to be a consequence of excitation of the ionized target to high-lying states, we find a strong dependence between the target and scattered projectile excitations.

physics.atom-ph↗

arXiv2026

Electron capture induced fragmentation of CO$_2^{3+}$: Influence of projectile charge on sequential and concerted break-up pathways

We investigate the $\text{O}^+:\text{C}^+:\text{O}^+$ fragmentation channel of CO$_2^{3+}$ produced in slow collisions with Ar$^{q+}$ projectiles ($4 \le q \le 16$, velocities $\approx 0.3$ a.u). Using the native-frames method, we disentangle the sequential and concerted break-up processes and their corresponding kinetic energy release (KER) distributions. \emph{Ab initio} potential energy curves of CO$_2^{3+}$ are calculated and mapped to the KER spectra to identify the underlying electronic states involved in the fragmentation. While the sequential KER distributions remain nearly unchanged for across the projectile charge range, the concerted KER distributions exhibit pronounced but non-systematic variations with projectile charge. In addition, a low KER feature around 15.5 eV -- previously associated with sequential break-up in electron and proton impact -- is observed for Ar$^{4+}$ impact and, to a lesser extent, for Ar$^{6+}$ impact. It originates predominantly from concerted break-up of the low-lying $^2\Pi_\text{g}$ and $^{2,4}\Pi_\text{u}$ states. Branching ratios of the two break-up pathways deviate from simple monotonic trends for certain projectiles, but barring these exceptions, the fraction of concerted break-up decreases with increasing $q$, while that for sequential break-up increases. These findings underscore the necessity of accounting for the detailed electronic structure of the projectile, rather than its charge alone, to achieve a comprehensive understanding of collisional dynamics in slow, highly charged ion collisions.

physics.atom-ph↗

arXiv2025

Isomer effects on neutral-loss dissociation channels of nitrogen-substituted PAH dications

We investigate two nitrogen-containing isomers of polycyclic aromatic hydrocarbons (PAHs), quinoline (Q) and isoquinoline (IQ), of composition C$_9$H$_7$N in collisions with 7~keV O$^+$ and 48~keV O$^{6+}$ projectile ions. Employing ion-ion coincidence mass spectrometry, we determine branching ratios for H-loss, C$_2$H$_2$-loss, and HCN-loss dissociation channels of Q$^{2+}$ and IQ$^{2+}$. The overall contribution of HCN-loss is found to be the dominant decay channel. A comparison with the results of a parallel experiment on naphthalene, the simplest PAH, reveals that HCN-loss in both isomers has a higher propensity than the analogous C$_2$H$_2$-loss of naphthalene. The positional identity of the nitrogen atom in the two isomers mainly manifests in many-body fragmentation of their dications. Potential energy surfaces of Q$^{2+}$ and IQ$^{2+}$ are further computed to explore complete fragmentation mechanisms. Parent dications (Q$^{2+}$ and IQ$^{2+}$) are identified to isomerize via seven-membered ring structures prior to elimination of C$_2$H$_2$ and HCN. While prompt dissociation is the primary pathway, the dominant channel of each neutral-loss class also exhibits delayed fragmentation.

physics.chem-ph↗