Strong-field ionization and AC-Stark shifted Rydberg states in OCS

We present theoretical results for intensity-dependent above-threshold ionization (ATI) spectra from oriented OCS molecules probed by intense femtosecond laser pulses with wavelengths of 800 and 400 nm. The calculations were performed using the time-dependent Schroodinger equation within the single-active-electron approximation and including multielectron polarization effects. The results are in qualitative agreement with experimental data [Yu et al., J. Phys. B: At. Mol. Opt. Phys. 50, 235602 (2017)]. In particular, characteristic features in the ATI spectra which correspond to resonant multiphoton ionization via highly-excited Rydberg states are captured by the theory.Comment: 3 figure

Ionization of 1D and 3D oriented asymmetric top molecules by intense circularly polarized femtosecond laser pulses

We present a combined experimental and theoretical study on strong-field ionization of a three-dimensionally oriented asymmetric top molecule, benzonitrile (C$_7$H$_5$N), by circularly polarized, nonresonant femtosecond laser pulses. Prior to the interaction with the strong field, the molecules are quantum-state selected using a deflector, and 3-dimensionally (3D) aligned and oriented adiabatically using an elliptically polarized laser pulse in combination with a static electric field. A characteristic splitting in the molecular frame photoelectron momentum distribution reveals the position of the nodal planes of the molecular orbitals from which ionization occurs. The experimental results are supported by a theoretical tunneling model that includes and quantifies the splitting in the momentum distribution. The focus of the present article is to understand strong-field ionization from 3D-oriented asymmetric top molecules, in particular the suppression of electron emission in nodal planes of molecular orbitals. In the preceding article [Dimitrovski et al., Phys. Rev. A 83, 023405 (2011)] the focus is to understand the strong-field ionization of one-dimensionally-oriented polar molecules, in particular asymmetries in the emission direction of the photoelectrons.Comment: 12 pages, 9 figure

Lineshape Models in Inner-shell Photoelectron Spectra of Free Molecules and Clusters

Investigating the nature of molecules and clusters is of paramount importance for our understanding of the composition and the properties of matter. X-ray photoelectron spectroscopy is one of the most powerful techniques for obtaining information at the fundamental level about molecules and clusters. Our interest in this particular kind of spectroscopy derives from its ability to probe individual atoms in a molecule and their chemical surrounding. Experimental core-level photoelectron spectra show great complexity, even for simple molecules. Hence, developing theoretical lineshapes to model and interpret experimental spectra is necessary. This thesis is devoted to the development of novel theoretical methods for modeling x-ray photoelectron spectra of molecules and clusters. It also demonstrates how these models can be used as means of extracting chemical information from experimental spectra. In this thesis, the carbon 1s photoelectron spectrum of gas-phase ethanol has been investigated by calculations, and found to be significantly influenced by the presence of a conformational equilibrium. Furthermore, theoretical models have been used to analyze inner-shell photoelectron spectra of clusters made up of either argon, methane, or methanol molecules. With the help of these models we have been able to interpret the experimental spectra in terms of chemical shifts, vibrations, and the chemical surrounding of atoms (molecules) in the cluster. The results are very interesting and will, hopefully, contribute to the development of the current understanding of the structures and properties of clusters

Formation and Growth of Clusters of Sulfur Dioxide

Formation and growth of neutral SO2 clusters is investigated in an adiabatic-expansion setup by means of sulfur 2p (S2p) photoelectron spectroscopy and theoretical modeling. The shift in S2p ionization energy between the cluster and a single molecule, i.e., IE(cluster)-IE(monomer), is recorded and used to monitor the mean cluster size over a wide range of expansion conditions. The produced clusters were shown to fall into two different size regimes. Comparison between theoretical simulations and experimental observations suggests that while the smallest clusters belong to the ultrafine particle mode and have a liquid-like structure, the larger clusters belong to the accumulation mode of fine particles and possibly have a frozen cluster core. The transition between the two size/structure regimes occurs over a narrow interval in expansion conditions and may possibly reflect a change in growth mechanism from monomer addition to growth by cluster-cluster collisions

Evaluation of the Adsorption Efficiency of Graphene Oxide Hydrogels in Wastewater Dye Removal: Application of Principal Component Analysis

Industrial dye wastewater is one of the major water pollution problems. Adsorbent materials are promising strategies for the removal of water dye contaminants. Herein, we provide a statistical and artificial intelligence study to evaluate the adsorption efficiency of graphene oxide-based hydrogels in wastewater dye removal by applying Principal Component Analysis (PCA). This study aims to assess the adsorption quality of 35 different hydrogels. We adopted different approaches and showed the pros and cons of each one of them. PCA showed that alginate graphene oxide-based hydrogel (without polyvinyl alcohol) had better tolerance in a basic medium and provided higher adsorption capacity. Polyvinyl alcohol sulfonated graphene oxide-based hydrogels are suitable when higher adsorbent doses are required. In conclusion, PCA represents a robust way to delineate factors affecting hydrogel selection for pollutant removal from aqueous solutions