Anticrossing effects in Stark spectra of helium

Łabuda

Pranszke

2019

IJMS

The present work focuses on unraveling the collisional processes leading to the fragmentation of the gas-phase furan molecules under the He+ and He2+ cations impact in the energy range 5–2000 eV. The presence of different mechanisms was identified by the analysis of the optical fragmentation spectra measured using the collision-induced emission spectroscopy (CIES) in conjunction with the ab initio calculations. The measurements of the fragmentation spectra of furan were performed at the different kinetic energies of both cations. In consequence, several excited products were identified by their luminescence. Among them, the emission of helium atoms excited to the 1s4d 1D2, 3D1,2,3 states was recorded. The structure of the furan molecule lacks an He atom. Therefore, observation of its emission lines is spectroscopic evidence of an impact reaction occurring via relocation of the electronic charge between interacting entities. Moreover, the recorded spectra revealed significant variations of relative band intensities of the products along with the change of the projectile charge and its velocity. In particular, at lower velocities of He+, the relative cross-sections of dissociation products have prominent resonance-like maxima. In order to elucidate the experimental results, the calculations have been performed by using a high level of quantum chemistry methods. The calculations showed that in both impact systems two collisional processes preceded fragmentation. The first one is an electron transfer from furan molecules to cations that leads to the neutralization and further excitation of the cations. The second mechanism starts from the formation of the He−C4H4O+/2+ temporary clusters before decomposition, and it is responsible for the appearance of the narrow resonances in the relative cross-section curves.

Section: Introductionmentioning

confidence: 99%

Charge Transfer, Complexes Formation and Furan Fragmentation Induced by Collisions with Low-Energy Helium Cations

Łabuda

Pranszke

2019

IJMS

“…It is well-known that branching ratios and lifetimes of certain states may be modified by electric fields via Stark mixing. Not only extremely high electric fields [52][53][54][55] can affect the system, but also the residual electric field present in the chamber can influence on the wave functions of the excited states [24]. The states having the same value of the total angular momentum quantum number j are the most prone to such mixing [50].…”

Section: Populations Of H (N)mentioning

confidence: 99%

Interactions of protons with furan molecules studied by collision-induced emission spectroscopy at the incident energy range of 50–1000 eV

Pranszke

2016

Eur. Phys. J. D

Abstract.Investigations of the ion-molecule reactions provide insight into many fields ranging from the stellar wind interaction with interstellar media, up to medicine and industrial applications. Besides the applications, the understanding of these processes is itself a problem of fundamental importance. Thus, interactions of protons with the gas-phase furan molecules have been investigated for the first time in the energy range of 50-1000 eV exploiting collision-induced emission spectroscopy. Recorded spectra reveal emission of the atomic H β to H θ lines of the hydrogen Balmer series and the molecular bands of vibrationally and rotationally excited diatomic CH fragments created in the A 2 Δ and B 2 Σ − electronic states. The measurements of the emission yields of the excited fragments by recording their intensities at different projectile energies have been performed. The highest yields have been observed for production of hydrogen atoms which intensities rapidly decreased with increasing principal quantum number n. From the H (n = 4-7) intensity ratios depopulation factors of hydrogen excited states have been determined at each impact energy and possible collisional mechanisms leading to enhanced production of the hydrogen atoms have been suggested. We compare and discuss our results with improved data set of proton collisions with tetrahydrofuran (THF) molecules, the hydrogenated derivatives of furan.

“…It is well-known that electric fields via Stark mixing may influence the branching ratios and lifetimes of specific states. High electric field strengths alter the populations [ 97 , 98 , 99 , 100 ], but the remnant electric field existing in the collision cell can also modify the wave functions of the excited states [ 101 ]. The electric field strengths higher than 0.22 V/cm were estimated by us previously for H + projectiles [ 26 ].…”

Section: Resultsmentioning

confidence: 99%

Neutral Dissociation of Pyridine Evoked by Irradiation of Ionized Atomic and Molecular Hydrogen Beams

2021

IJMS

The interactions of ions with molecules and the determination of their dissociation patterns are challenging endeavors of fundamental importance for theoretical and experimental science. In particular, the investigations on bond-breaking and new bond-forming processes triggered by the ionic impact may shed light on the stellar wind interaction with interstellar media, ionic beam irradiations of the living cells, ion-track nanotechnology, radiation hardness analysis of materials, and focused ion beam etching, deposition, and lithography. Due to its vital role in the natural environment, the pyridine molecule has become the subject of both basic and applied research in recent years. Therefore, dissociation of the gas phase pyridine (C5H5N) into neutral excited atomic and molecular fragments following protons (H+) and dihydrogen cations (H2+) impact has been investigated experimentally in the 5–1000 eV energy range. The collision-induced emission spectroscopy has been exploited to detect luminescence in the wavelength range from 190 to 520 nm at the different kinetic energies of both cations. High-resolution optical fragmentation spectra reveal emission bands due to the CH(A2Δ → X2Πr; B2Σ+ → X2Πr; C2Σ+ → X2Πr) and CN(B2Σ+ → X2Σ+) transitions as well as atomic H and C lines. Their spectral line shapes and qualitative band intensities are examined in detail. The analysis shows that the H2+ irradiation enhances pyridine ring fragmentation and creates various fragments more pronounced than H+ cations. The plausible collisional processes and fragmentation pathways leading to the identified products are discussed and compared with the latest results obtained in cation-induced fragmentation of pyridine.