arXiv subjects

Antonis Hadjipittas

Publications and source records attributed to Antonis Hadjipittas.

4 recordsLinked to original sources

arXiv2023

Potential energy curves of molecular nitrogen up to $N_2^{4+}$

The potential energy curves for molecular ions up to $N_2^{4+}$ are calculated in an ab initio manner using the multi configurational self-consistent field method. Specifically, we implement in an automatic way a previously used double loop optimisation scheme within the multi configurational self-consisted field method. We obtain the potential energy curves up to $N_2^{4+}$ ions with any combination of core, inner valence, and outer valence holes. Finally, we provide the code used to generate these potential energy curves.

physics.atom-ph↗

arXiv2020

Sequential single-photon and direct two-photon absorption processes for Xe interacting with attosecond XUV pulses

We investigate the interaction of Xe with isolated attosecond XUV pulses. Specifically, we calculate the ion yields and determine the pathways leading to the formation of ionic charged states up to Xe$^{5+}$. To do so, in our formulation we account for single-photon absorption, sequential multi-photon absorption, direct two-photon absorption, single and double Auger decays, and shake-off. We compare our results for the ion yields and for ion yield ratios with recent experimental results obtained for 93 eV and 115 eV attosecond XUV pulses. In particular, we investigate the role that a sequence of two single-photon ionization processes plays in the formation of Xe$^{4+}$. We find that each one of these two processes ionizes a core electron and thus leads to the formation of a double core-hole state. Remarkably, we find that the formation of Xe$^{5+}$ involves a direct two-photon absorption process and the absorption of a total of three photons.

physics.atom-ph↗

arXiv2020

Carbon monoxide interacting with free-electron-laser pulses

We study the interaction of a heteronuclear diatomic molecule, carbon monoxide, with a free-electron laser (FEL) pulse. We compute the ion yields and the intermediate states by which the ion yields are populated. We do so using rate equations, computing all relevant molecular and atomic photoionisation cross-sections and Auger rates. We find that the charge distribution of the carbon and oxygen ion yields differ. By varying the photon energy, we demonstrate how to control higher-charged states being populated mostly by carbon or oxygen. Moreover, we identify the differences in the resulting ion yields and pathways populating these yields between a homonuclear molecule, molecular nitrogen, and a heteronuclear molecule, carbon monoxide, interacting with an FEL pulse. These two molecules have similar electronic structure. We also identify the proportion of each ion yield which accesses a two-site double-core-hole state and tailor pulse parameters to maximise this proportion.

physics.atom-ph↗

arXiv2019

Pulse dependence of prevalent pathways in xenon driven by an x-ray free-electron-laser pulse

We study the interaction of xenon with an 850 eV photon energy FEL pulse. We do so by employing a Monte-Carlo technique. We compute the single-photon ionisation cross sections and Auger rates, used in the Monte-Carlo technique, by adopting to atoms a formalism we previously developed for diatomic molecules. We determine the yields of the ion states of driven xenon and compare with previously obtained experimental results. To better understand the yields obtained, we identify the prevalent pathways leading to the formation of each final ion state of xenon. We gain further insight into the high yields of highly-charged ion states by comparing the yields and dominant pathways of these ion states of xenon when driven by different FEL pulses that have the same energy. We show that higher-charged ion states have higher yields when xenon is driven by longer-duration pulses due to Auger cascades taking place between subsequent single-photon ionisations.

physics.atom-ph↗